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SOUTHERN BRANCH,

OF C7VLIF0RNIA,

HISTORY OF THE THEORY OF NUMBERS

VOLUME I

DIVISIBILITY AND PRIMALITY

By Leonard Eugene Dickson

Professor of Mathematics in the University of Chicago

Published by the Carnegie Institution of Washington
Washington, 1919

/ 1 i 5 'J

CARNEGIE INSTITUTION OF WASHINGTON
Publication No. 256, Vol. I

PRESS OF GIBSON BROTHERS
WASHINGTON. D. C.

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'^vi-^ r7' Mathenrstical
2^H-j Sciences

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PREFACE.

libraiy

The efforts of Cantor and his collaborators show that a chronological
history of mathematics down to the nineteenth century can be written in
four large volumes. To cover the last century with the same elaborateness,
it has been estimated that about fifteen volumes would be required, so
extensive is the mathematical literature of that period. But to retain the
chronological order and hence devote a large volume to a period of at most
seven years would defeat some of the chief purposes of a history, besides
making it very inconvenient to find all of the material on a particular topic.
In any event there is certainly need of histories which treat of particular
branches of mathematics up to the present time.

The theory of numbers is especially entitled to a separate history on

account of the great interest which has been taken in it continuously through

the centuries from the time of Pythagoras, an interest shared on the one

extreme by nearly every noted mathematician and on the other extreme

^ by numerous amateurs attracted by no other part of mathematics. This

v history aims to give an adequate account of the entire literature of the

\ theory of numbers. The first volume presents in twenty chapters the

material relating to divisibility and primality. The concepts, results, and

Jl authors cited are so numerous that it seems appropriate to present here an

introduction which gives for certain chapters an account in untechnical

language of the main results in their historical setting, and for the remaining

• chapters the few remarks sufficient to clearly characterize the nature of their

v^, contents.

J' ' ' Perfect numbers have engaged the attention of arithmeticians of every
*»>• century of the Christian era. It was while investigating them that Fermat
discovered the theorem which bears his name and which forms the basis
of a large part of the theory of numbers. A_perfect number is one, like
6 = 1+2+3, which equals the sum of its divisors other than itself . Euclid
,. proved that 2^~'^{2^ — \) is a perfect numbeflf 2^ — 1 is a prime. For p = 2,
3, 5, 7, the values 3, 7, 31, 127 of 2''-l are primes, so that 6, 28, 496, 8128
are perfect numbers, as noted by Nicomachus (about A. D. 100). A manu-
script dated 1456 correctly gave 33550336 as the fifth perfect number; it cor-
* ! responds to the value 13 of p. Very many early writers believed that 2^ — 1
I is a prime for every odd value of p. But in 1536 Regius noted that

2^-1 = 511 = 7-73, 211-1=2047 = 23-89

are not primes and gave the above fifth perfect number. Cataldi, who
founded at Bologna the most ancient known academy of mathematics,

IV PREFACE.

noted in 1603 that 2'' — 1 is composite if p is composite and verified that it is
a prime for p = 13, 17, and 19; but he erred in stating that it is also a prime
for p = 23, 29, and 37. In fact, Fermat noted in 1640 that 2'-'-l has the
factor 47, and 2^'-l the factor 223, while Euler observed in 1732 that
2'' — 1 has the factor 1103. Of historical importance is the statement made
by Mersenne in 1644 that the first eleven perfect numbers are given by
2P-i(2P_i) for p = 2, 3, 5, 7, 13, 17, 19, 31, 67, 127, 257; but he erred at
least in including 67 and excluding 61, 89, and 107. That 2" — 1 is com-
posite was proved by Lucas in 1876, while its actual factors were found by
Cole in 1903. The primality of 2^^ — 1, a number of 19 digits, was estab-
lished by Pervusin in 1883, Seelhoff in 1886, and Hudelot m 1887. Both
Powers and Fauquembergue proved in 1911-14 that 2^^ — 1 and 2^°^ — 1 are
primes. The primality of 2'^ — 1 and 2™ — 1 had been estabhshed by Euler
and Lucas respectively. Thus 2^— 1 is known to be a prime, and hence lead
to a perfect number, for the twelve values 2, 3, 5, 7, 13, 17, 19, 31, 61, 89,
107 and 127 of p. Since 2^' — 1 is known (pp. 15-31) to be composite for 32
primes p ^257, only the eleven values p = 137, 139, 149, 157, 167, 193, 199,
227, 229, 241, 257 now remain in doubt.

Descartes stated in 1638 that he could prove that every even perfect
number is of Euclid's type and that every odd perfect number must be of the
form ps^, where p is a prime. Euler's proofs (p. 19) were published after his
death. Xd. immediate proof of the former fact was given by Dickson (p. 30).
According to Sylvester (pp. 26-27), there exists no odd perfect number with
fewer than six distinct prime factors, and none with fewer than eight if not
divisible by 3. But the question of the existence of odd perfect numbers
remains unanswered.

A multiply perfect number, like 120 and 672, is one the sum of whose
divisors equals a multiple of the number. They were actively investigated
during the years 1631-1647 by IMersenne, Fermat, St. Croix, Frenicle, and
Descartes. Many new examples hav^e been found recently by American
writers.

Two numbers are called amicable if each equals the sum of the aliquot
divisors of the other, where an aliquot divisor of a number means a divisor
other than the number itself. The pair 220 and 284 was known to the
Pythagoreans. In the ninth century, the Arab Thabit ben Korrah noted
that 2"/!« and 2"s are amicable numbers if /j=3-2''-l, t = 2>'2'^^-l and s =
9.22"-! _i are all primes, and n> 1. This result leads to amicable numbers
for n = 2 (giving the above pair), n = 4 and n = 7, but for no further value
^ 200 of n. The chief investigation of amicable numbers is that by Euler
who listed (pp. 45, 46) 62 pairs. At the age of 16, Paganini announced in
1866 the remarkable new pair 1184 and 1210. A few new pairs of very
large numbers have been found by Legendre, Seelhoff, and Dickson.

PREFACE. V

Interesting amicable triples and amicable numbers of higher order have
been recently found by Dickson and Poulet (p. 50).

Although it had been employed in the study of perfect and amicable
numbers, the explicit expression for the sum a{n) of all the divisors of n is
reserved for Chapter II, in which is presented the history of Fermat's two
problems to solve (T(x^)=y^ and <t{x^) =y^ and John Wallis's problem to find
solutions other than a; = 4 and y = 5 oi (T{x^)=o-{y^).

Fermat stated in 1640 that he had a proof of the fact, now known as
Fermat's theorem, that, if p is any prime and x is any integer not divisible
by p, then x^~^ — l is divisible by p. This is one of the fundamental theo-
rems of the theory of numbers. The case x = 2 was known to the Chinese as
early as 500 B. C. The first published proof was given by Euler in 1736.
Of first importance is the generalization from the case of a prime p to any
integer n, published by Euler in 1760: if (/)(n) denotes the munber of positive
integers not exceeding n and relatively prime to n, then x*^"^ — 1 is divisible
. by n for every integer x relatively prime to n. Another elegant theorem
states that, if p is a prime, l+jl-2-3. . . .{p — l)\ is divisible by p; it was
first pubUshed by Waring in 1770, who ascribed it to Sir John Wilson. This
theorem was stated at an earlier date in a manuscript by Leibniz, who with
Newton discovered the calculus. But Lagrange was the first one to publish
(in 1773) a proof of Wilson's theorem and to observe that its converse is
true. In 1801 Gauss stated and suggested methods to prove the generali-
zation of Wilson's theorem: if P denotes the product of the positive integers
less than A and prime to A, then P+1 is divisible by A if A =4, p"" or 2p"*,
where p is an odd prime, while P — 1 is divisible by A if A is not of one of
these three forms. A very large number of proofs of the preceding theorems
are given in the first part of Chapter III. Various generalizations are then
presented (pp. 84-91). For instance, if iV = p/' . . . p/*, where Pi, ..., p«
are distinct primes,

a^-(a^/P'+ . . . +a^/PO + (a^/P'P'+ ...)-••• . +(-l)''a^/^---P''

is divisible by N, a fact due to Gauss for the case in which a is a prime.

Many cases have been found in which o"~^ — 1 is divisible by n for a
composite number n. But Lucas proved the following converse of Fermat's
theorem : if a^ — 1 is divisible by n when x = n — l, but not when x is a divisor
|<n — 1 of 71 — 1, then w is a prime.

Any integral symmetric function of degree d of 1, 2, . . ., p — 1 with
I integral coefficients is divisible by the prime p if c^ is not a multiple of p — 1.
A generalization to the case of a divisor p" is due to Meyer (p. 101) . Nielsen
proved in 1893 that, if p is an odd prime and if k is odd and l<fc<p — 1, the
sum of the products of 1, 2, . . ., p — 1 taken A; at a time is divisible by p^.
Taking fc = p — 2, we see that if p is a prime > 3 the numerator of the fraction

A

VI PREFACE.

equal to 1 + 1/2+1/3+ . . . +l/(p — 1) is divisible by p'^, a result first proved
by Wolstenholme in 1862. Sylvester stated in 1866 that the sum of all
products of n distinct numbers chosen from 1, 2, . . . , w is divisible by each
prime > n + 1 which is contained in any term of the set m — n + 1 , . . . , w, m + 1 .
There are various theorems analogous to these.

In Chapter IV are given properties of the quotient {uP~^ — l)/p, which
plays an important role in recent investigations on Fermat's last theorem
(the impossibiUty of x'^-\-y^ = z^ if p>2), the history of which will be treated
in the final chapter of Volume II. Some of the present papers relate to
(w*^"^ — 1)/«, where n is not necessarily a prime.

TMiile Euler's ^-function was defined above in order to state his general-
ization of Fermat's theorem, its numerous properties and generalizations
are reserved for the long Chapter V. In 1801 Gauss gave the result that
4>{d^ + . . . -\-<i>{dk) = n, if di, . . . , d^ are the divisors of n; this was generalized
by Laguerre in 1872, H. G. Cantor in 1880, Busche in 1888, Zsigmondy in
1893, Vahlen in 1895, Elliott in 1901, and Hammond in 1916. In 1808
Legendre proved a simple formula for the number of integers ^ n which are
divisible by no one of any given set of primes. The asymptotic value of
(f>{l)-\- . . . +0(G) for G large was discussed by Dirichlet in 1849, Mertens in
1874, Perott in 1881, Sylvester in 1883 and 1897, Cesaro in 1883 and 1886-8,
Berger in 1891, and Kronecker in 1901. The solution of 4>{x)=g was treated
by Cayley in 1857, Mmin in 1897, Pichler in 1900, Carmichael in 1907-9,
Ranum in 1908, and Cunningham in 1915. H. J. S. Smith proved in 1875
that the m-rowed determinant, ha\ing as the element in the ith row and
ji\i column any function fib) of the greatest common divisor 5 of i and j,
equals the product of F{\), F{2),. . ., F(m), where

F(m)=/(m)-2/g)+2/(^J-...., m = py

In particular, F{m)=<t>{m) if f{8)=8. In several papers (pp. 128-130)
Cesaro considered analogous determinants. The fact that 30 is the largest
number such that all smaller numbers relatively prime to it are primes was
first proved by Schatunowsky in 1893.

A. Thacker in 1850 evaluated the sum 4>k{n) of the kth. powers of the
integers ^n which are prime to n. His formula has been expressed m^
various symbolic forms by Ces^o and generalized by Glaisher and Nielsen./
Crelle had noted in 1845 that <piin) = |n0( n). In 1869 Schemmel considered
the number of sets of n consecutive integers each < m and prime to m. In
connection with linear congruence groups, Jordan evaluated the number of
different sets of k positive integers ^?i whose greatest common divisor is
prime to n. This generalization of Euler's (^-function has properties as
simple as the latter function and occurs in many papers under a variety of
notations. It in turn has been generalized (pp. 151-4).

PREFACE. VII

The properties of the set of all irreducible fractions, arranged in order of
magnitude, whose numerators are ^ m and denominators are ^ n (called a
Farey series if m = n), have been discussed by many writers and applied to
the approximation of numbers, to binary quadratic forms, to the composi-
tion of linear fractional substitutions, and to geometry (pp. 155-8).

Some of the properties of periodic decimal fractions are already familiar
tq the reader in view of his study of arithmetic and the chapter of alge-
bra dealing with the sum to infinity of a geometric progression. For the
generalization to periodic fractions to any base h, not necessarily 10, the
length of the period of the periodic fraction for 1/d, where d is prime to h,
is the least positive exponent e such that h^ — \ is divisible by d. Hence this
Chapter VI, which reports upon more than 160 papers, is closely related to
the following chapter and furnishes a concrete introduction to it.

The subject of exponents and primitive roots is one of the important
topics of the theory of numbers. To present the definitions in the customary,
compact language, we shall need the notion of congruence. If the differ-
ence of two integers a and 6 is divisible by m, they are called congruent
modulo m and we write a=& (mod m). For example, 8=2 (mod 6). If
n'= 1 (mod m), but n*^ 1 (mod m) for 0<s<e, we say that n belongs to the
exponent e modulo m. For example, 2 and 3 belong to the exponent 4
modulo 5, while 4 belongs to the exponent 2. In view of Euler's generaliza-
tion of Fermat's theorem, stated above, e never exceeds 0(m). If n belongs
to this maximum exponent ^(n) modulo m, n is called a primitive root of m.
For example, 2 and 3 are primitive roots of 5, while 1 and 4 are not. Lam-
bert stated in 1769 that there exists a primitive root of any prime p, and
Euler gave a defective proof in 1773. In 1785 Legendre proved that there
are exactly 4>{e) numbers belonging modulo p to any exponent e which
divides p — 1. In 1801 Gauss proved that there exist primitive roots of m
if and only if m = 2, 4, p* or 2p*, where p is an odd prime. In particular, for
a primitive root a of a prime modulus p and any integer N not divisible
by p, there is an exponent ind N, called the index of N by Gauss, such that
N=a''"^^ (mod p). Indices play a role similar to logarithms, but we re-
quire two companion tables for each modulus p. The extension to a power
of prime modulus is immediate. For a general modulus, systems of indices
were employed by Dirichlet in 1837 and 1863 and by Kronecker in 1870.
Jacobi's Canon Arithmeticus of 1839 gives companion tables of indices for
each prime and power of a prime < 1000. Cunningham's Binary Canon of
1900 gives the residues of the successive powers of 2 when divided by each
prime or power of a prime < 1000 and companion tables showing the powers
of 2 whose residues are 1, 2, 3, . . .. In 1846 Arndt proved that, if ^ is a
primitive root of the odd prime p, g belongs to the exponent p"~"^(p — 1)
modulo p'* if and only ii G = g^~^ — 1 is divisible by p^, but not by p^'^\ where

VIII PREFACE.

X<n; taking X= 1, we see that, if G is not divisible by p^, g' is a primitive
root of p^ and of all higher powers of p. This Chapter VII presents many
more theorems on exponents, primitive roots, and binomial congruences, and
cites various lists of primitive roots of primes < 10000.

Lagrange proved easily that a congruence of degree n has at most n roots
if the modulus is a prime. Lebesgue found the number of sets of solutions of
01^1"*+ • • • -\-akXk"=a (mod p), when p is a prime such that p — 1 is divisible
by m. Konig (p. 226) employed a cyclic determinant and its minors to find
the exact number of real roots of any congruence in one unknown; Gegen-
bauer (p. 228) and Rados (p. 233) gave generalizations to congruences in
several unknowns.

Galois's introduction of imaginary roots of congruences has not only
led to an important extension of the theory of numbers, but has given rise
to wide generalizations of theorems which had been obtained in subjects
like linear congruence groups by applying the ordinary theory of numbers.
Instead of the residues of integers modulo p, let us consider the residues of
polynomials in a variable x with integral coefficients with respect to two
moduH, one being a prime p and the other a polynomial f{x) of degree n
which is irreducible modulo p. The residues are the p" polynomials in x of
degree n — 1 whose coefficients are chosen from the set 0, 1, . . . , p — 1 . These
residues form a Galois field within which can be performed addition, sub-
traction, multiplication, and division (except by zero) . As a generahzation
of Fermat's theorem, Galois proved that the power p" — 1 of any residue
except zero is congruent to unity with respect to our pair of moduli p and
f{x). He avoided our second modulus f{x) by introducing an undefined
imaginary root i of f{x) = 0 (mod p) and considering the residues modulo p
of polynomials in i; but the above use of the two moduH affords the only
logical basis of the theory. In view of the fullness of the reports in the text
(pp. 233-252) of the papers on this subject, further comments here are
unnecessary. The final topics of this long Chapter VIII are cubic congru-
ences and miscellaneous results on congruences and possess little general
interest.

In Chapter IX are given Legendre's expression for the exponent of the
highest power of a prime p which divides the factorial 1-2. . .m, and the
generalization to the product of any integers in arithmetical progression;
many theorems on the divisibility of one product of factorials by another
product and on the residues of multinomial coefficients ; various determina-
tions of the sign in 1-2... (p — l)/2==tl (mod p); and miscellaneous
congruences involving factorials.

In the extensive Chapter X are given many theorems and formulas
concerning the sum of the kth. powers of all the divisors of n, or of its even or
odd divisors, or of its divisors which are exact sth powers, or of those divisors

PREFACE. IX

whose complementary divisors are even or odd or are exact sth powers, and
the excess of the sum of the A;th powers of the divisors of the form 4m +1 of
a number over the sum of the A;th powers of the divisors of the form 4m -f 3,
as well as more technical sums of divisors defined on pages 297, 301-2, 305,
307-8, 314-5 and 318. For the important case k = 0, such a sum becomes
the number of the divisors in question. There are theorems on the number
of sets of positive integral solutions of UiU^. . .Uk = n or of x''y^ = n. Also
Glaisher's cancellation theorems on the actual divisors of numbers (pp.
^' 310-11, 320-21). Scattered through the chapter are approximation and
asymptotic formulas involving some of the above functions.

In Chapter XI occur Dirichlet's theorem on the number of cases in the

division of n by 1, 2, . . . , p in turn in which the ratio of the remainder to the

divisor is less than a given proper fraction, and the generalizations on pp.

330-1; theorems on the number of integers ^n which are divisible by no

,( exact sth power > 1 ; theorems on the greatest divisor which is odd or has

/ specified properties; many theorems on greatest coromon divisor and least

I common multiple ; and various theorems on mean values and probability.

' The casting out of nines or of multiples of 11 or 7 to check arithmetical

computations is of early origin. This topic and the related one of testing

the divisibility of one number by another have given rise to the numerous

elementary papers cited in Chapter XII.

The frequent need of the factors of numbers and the excessive labor
required for their direct determination have combined to inspire the
construction of factor tables of continually increasing limit. The usual
method is essentially that given by Eratosthenes in the third century B. C.
A special method is used by Lebon (pp. 355-6). Attention is called to
Lehmer's Factor Table for the First Ten Millions and his List of Prime
Numbers from 1 to 10,006,721, published in 1909 and 1914 by the Carnegie
Institution of Washington. Since these tables were constructed anew with
the greatest care and all variations from the chief former tables were taken
account of, they are certainly the most accurate tables extant. Absolute
accuracy is here more essential than in ordinary tables of continuous func-
tions. Besides giving the history of factor tables and lists of primes, this
Chapter XIII cites papers which enumerate the primes in various intervals,
prime pairs (as 11, 13), primes of the form 4n+l, and papers listing primes
written to be base 2 or large primes.

Chapter XIV cites the papers on factoring a number by expressing it as
a difference of two squares, or as a sum of two squares in two ways, or by use
of binary quadratic forms, the final digits, continued fractions. Pell equa-
tions, various small moduli, or miscellaneous methods.

Fermat expressed his belief that Fn = 2^"+l is a prime for every value of n.
While this is true if n = 1, 2, 3, 4, it fails forn = 5 as noted by Euler. Later,

X PREFACE.

Gauss proved that a regular polygon of m sides can be constructed by ruler
and compasses if m is a product of a power of 2 and distinct odd primes each
of the form Fn, and stated correctly that the construction is impossible if m
is not such a product. In view of the papers cited in Chapter XV, F„ is
composite if n = 5, 6, 7, 8, 9, 11, 12, 18, 23, 36, 38 and 73, while nothing is
known for other values >4 of n. No conoment will be made on the next
chapter which treats of the factors of numbers of the form o"±6" and of
certain trinomials.

In Chapter XVII are treated questions on the divisors of terms of a
recurring series and in particular of Lucas' functions

a — o

where a and h are roots oi x'^ — Px-\-Q = Q, P and Q being relatively prime
integers. By use of these functions, Lucas obtained an extension of Euler's
generaUzation of Fermat's theorem, which requires the correction noted by
Carmichael (p. 406), as well as various tests for primality, some of which
have been emploj^ed in investigations on perfect numbers. Many papers on
the algebraic theory of recurring series are cited at the end of the chapter.

Euchd gave a simple and elegant proof that the number of primes is infi-
nite. For the generalization that every arithmetical progression n, n+m,
n-\-2m,. . ., in which n and m are relatively prime, contains an infinitude
of primes, Legendre offered an insufficient proof, while Dirichlet gave his
classic proof by means of infinite series and the classes of binary quadratic
forms, and extended the theorem to complex integers. Mertens and others
obtained simpler proofs. For various special arithmetical progressions, the
theorem has been proved in elementary ways by many writers. Dirichlet
also obtained the theorems that, if a, 26, and c have no common factor,
ax'^+2hxy-\-cy^ represents an infinitude of primes, while an infinitude of these
primes are representable by any given linear form Mx+N with M and N
relatively prime, pro\^ded a, h, c, M, N are such that the quadratic and linear
forms can represent the same number.

No complete proof has been found for Goldbach's conjecture in 1742 that
every even integer is a sum of two primes. One of various analogous un-
proved conjectures is that every even integer is the difference of two consec-
utive primes in an infinitude of ways (in particular, there exists an infinitude
of pairs of primes differing by 2). No comment will be made on the further
topics of this Chapter XVIII: polynomials representing numerous primes,
primes in arithmetical progression, tests for primality, number of primes
between assigned limits, Bertrand's postulate of the existence of at least one
prime between x and 2x — 2 for x>3, miscellaneous results on primes,
diatomic series, and asymptotic distribution of primes.

PREFACE. XI

If F(m)=2/(d), summed for all the divisors d of m, we can express
/(m) in terms of F by an inversion formula given in Chapter XIX along with
generalizations and related formulas. Bougaief called F{m) the numerical
integral of /(m).

The final Chapter XX gives many elementary results involving the digits
of numbers mainly when written to the base 10.

Since the history of each main topic is given separately, it has been
possible without causing confusion to include reports on minor papers and
isolated problems for the sake of completeness. In the cases of books and
journals not usually accessible, the reports are quite full with some indication
of the proofs. In other cases, proofs are given only when necessary to
differentiate the paper from others deriving the same result.

The references were selected mainly from the Subject Index of the Royal
Society of London Catalogue of Scientific Papers, volume 1, 1908 (with which
also the proof-sheets were checked), and the supplementary annual volumes
forming the International Catalogue of Scientific Literature, Jahrbuch
iiber die Fortschritte der Mathematik, Revue semestrielle des publications
math^matiques, Poggendorff's Handworterbuch, Kliigel's Mathematische
Worterbuch, Wolffing's Mathematischer Biicherschatz (a list of mathemat-
ical books and pamphlets of the nineteenth century), historical journals, such
as Bulletino di bibliografia e di storia delle scienze matematiche e fisiche,
Bolletino . . . . , BibUotheca Mathematica, Abhandlungen zur Geschichte
der mathematischen Wissenschaften, various histories and encyclopedias,
including the Enclyclop^die des sciences mathematiques. Further, the
author made a direct examination at the stacks of books and old journals
in the libraries of Chicago, California, and Cambridge Universities, and
Trinity College, Cambridge, and the excellent John Crerar Library at Chi-
cago. He made use of G. A. Plimpton's remarkable collection, in New
York, of rare books and manuscripts. In 1912 the author made an
extended investigation in the libraries of the British Museum, Kensington
Museum, Royal Society, Cambridge Philosophical Society, Bibliotheque
Nationale, Universite de Paris, St. Genevieve, I'lnstitut de France, Uni-
versity of Gottingen, and the Konigliche Bibhothek of Berlin (where there
is a separate index of the material on the theory of numbers). Many
books have since been borrowed from various libraries; the Ladies' and
other Diaries were loaned by R. C. Archibald.

At the end of the volume is a separate index of authors for each of the
twenty chapters, which will facilitate the tracing of the relation of a paper
to kindred papers and hence will be of special service in the case of papers
inaccessible to the reader. The concluding volume will have a combined
index of authors from which will be omitted minor citations found in the
chapter indices.

XII PREFACE.

The subject index contains a list of symbols; while [x] usually denotes
the greatest integer ^x, occasionally such square brackets are used to
inclose an addition to a quotation. The symbol * before an author's
name signifies that his paper was not available for report. The symbol f
before a date signifies date of death. Initials are given only in the first of
several immediately successive citations of an author.

Although those volumes of Euler's Opera Omnia which contain his Com-
mentationes Arithmeticae CoUectse have been printed, they are not yet
available; a table showing the pages of the Opera and the corresponding
pages in the present volume of this history will be given in the concluding
volume.

The author is under great obligations to the following experts in the
theory of numbers for numerous improvements resulting from their reading
the initial page proofs of this volume: R. D. Carmichael, L. Chanzy, A.
Cunningham, E. B. Escott, A. Gerardin, A. J. Kempner, D. N. Lehmer, E.
Maillet, L. S. Shively, and H. J. Woodall; also the benefit of D. E. Smith's
accurate and extensive acquaintance with early books and writers was for-
tunately secured ; and the author's special thanl<:s are due to Carmichael and
Kempner, who read the final page proofs with the same critical attention
as the initial page proofs and pointed out various errors and obscurities.
To these eleven men who gave so generously of their time to perfect this
volume, and especially to the last two, is due the gratitude of every devotee
of number theory who may derive benefit or pleasure from this history. In
return, such readers are requested to further increase the usefulness of this
work by sending corrections, notices of omissions, and abstracts of papers
marked not available for report, for insertion in the concluding volume.

Finally, this laborious project would doubtless have been abandoned soon
after its inception seven years ago had not President Woodward approved
it so spontaneously, urged its completion with the greatest thoroughness,
and given continued encouragement.

L. E. Dickson.
November, 1918.

^ TABLE OF CONTENTS.

Chapter. page.

I. Perfect, multiply perfect, and amicable numbers 3

\ 11. Formulas for the number and simi of divisors, problems of Fermat

and Wallis 51

III. Fermat's and Wilson's theorems, generalizations and converses;

symmetric functions of 1, 2, . . . , p— 1, modulo p 59

IV. Residue of (wp~^ — l)/p modulo p 105

V. Euler's (^function, generalizations; Farey series 113

VI. Periodic decimal fractions; periodic fractions; factors of 10" =•=!... . 159

VII. Primitive roots, exponents, indices, binomial congruences 181

VIII. Higher congruences 223

IX. Divisibility of factorials and multinomial coefficients 263

X. Sum and number of divisors 279

XI. Miscellaneous theorems on divisibility, greatest common divisor,

least common multiple 327

XII. Criteria for divisibility by a given number 337

XIII. Factor tables, lists of primes 347

v^IV. Methods of factoring 357 •

XV. Fermat numbers F„ = 22"+l 375

XVI. Factors of a"±6« 381

XVII. Recurring series; Lucas' Un, Vn 393

^VIII. Theory of prime numbers 413

XIX. Inversion of functions; Mobius' function ix{n); numerical integrals

and derivatives 441

XX. Properties of the digits of numbers 453

Author index 467

Subject index 484

1

(.

CHAPTER I.

PERFECT. MULTIPLY PERFECT. AND AMICABLE NUMBERS.
Perfect, Abundant, and Deficient Numbers.

By the aliquot parts or divisors of a number are meant the divisors,
including unity, which are less than the number. A number, like 6 = 1 -h
2+3, which equals the sum of its aliquot divisors is called perfect (voll-
kommen, vollstandig) . If the sum of the aliquot divisors is less than the
number, as is the case with 8, the number is called deficient (diminute,
defective, unvollkommen, unvollstandig, mangelhaft). If the sum of the
aliquot divisors exceeds the number, as is the case with 12, the number is
called abundant (superfluos, plus quam-perfectus, redundantem, exc^dant,
iibervollstandig, iiberflussig, iiberschiessende) .

Euclid^ proved that, if p = 1+2+2^+ • • • +2" is a prime, 2"p is a perfect
number. He showed that 2"p is divisible by 1, 2, . . . , 2", p, 2p, . . . , 2'*~^p,
but by no further number less than itself. By the usual theorem on
geometrical progressions, he showed that the sum of these divisors is 2"^.

The early Hebrews^" considered 6 to be a perfect number.

Philo Judeus^'' (first century A. D.) regarded 6 as the most productive
of all numbers, being the first perfect number.

Nicomachus^ (about A. D. 100) separated the even numbers (book I,
chaps. 14, 15) into abundant (citing 12, 24), deficient (citing 8, 14), and
perfect, and dwelled on the ethical import of the three types. The perfect
(I, 16) are between excess and deficiency, as consonant sound between
acuter and graver sounds. Perfect numbers will be found few and arranged
with fitting order; 6, 28, 496, 8128 are the only perfect numbers in the
respective intervals between 1, 10, 100, 1000, 10000, and they have the
property of ending alternately in 6 and 8. He stated that Euclid's rule
gives all the perfect numbers without exception.

Theon of Smyrna^ (about A. D. 130) distinguished between perfect
(citing 6, 28), abundant (citing 12) and deficient (citing 8) numbers.

^Elementa, liber IX, prop. 36. Opera, 2, Leipzig, 1884, 408.
^"S. Rubin, "Sod Hasfiroth" (secrets of numbers), Wien, 1873, 59; citation of the Bible,

Kings, II, 13, 19.
**Treatise on the account of the creation of the world as given by Moses, C. D. Young's

transl. of Philo's works, London, 1854, vol. 1, p. 3.
'Nicomachi Gerasini arithmeticse Ubri duo. Nunc primdm typis excusi, in lucem eduntur.

Parisiis, 1538. In officina Christian! WecheU. (Greek.)
Theologumena arithmeticae. Accedit Nicomachi Gerasini institutio arithmetica ad fidem

codicum Monacensium emendata. Ed., Fridericus Astius. Lipsiae, 1817. (Greek.)
Nicomachi Geraseni Pythagorei introductionis arithmeticae libri ii. Recensvit Ricardus

Hoche. Lipsiae, 1866. (Greek.)
'Theonis Smymaei philosophi Platonici expositio rerum mathematicarum ad legendum

Platonem utiHum. Ed., Ed. Hiller, Leipzig, 1878, p. 45.
Theonis Smymaei Platonici, Latin by Ismaele BuUialdo. Paris, 1644, chap. 32, pp. 70-72.

3

4 History of the Theory of Numbers. [Chap. I

lamblichus* (about 283-330) repeated in effect the remarks by Nico-
machus on perfect, abundant, and deficient numbers, but made erroneous
additions. He stated that there is one and but one perfect number in the
successive intervals between 1, 10, 100,..., 100000, etc., to infinity.
"Examples of a perfect number are 6, and 28, and 496, and 8128, and the like
numbers, alternately ending in 6 and 8." He remarked that the Pythag-
oreans called the perfect number 6 marriage, and also health and beauty
(on account of the integrity of its parts and the agreement existing in it).

Aurelius Augustinus^ (354-430) remarked that, 6 being the first perfect
number, God effected the creation in 6 daj's rather than at once, since the
perfection of the work is signified by the number 6. The sum of the aUquot
parts of 9 falls short of it; likewise for 10. But the sum of the aliquot
parts of 12 exceeds it.

Anicius Manhus Severinus Boethius^ (about 481-524), in a Latin exposi-
tion of the arithmetic of Nicomachus, stated that perfect numbers are rare,
easily counted, and generated in a very regular order, while abundant
(superfluos) and deficient (diminutos) numbers are found to an unlimited
extent and not in regular order. The perfect numbers below 10000 are
6, 28, 496, 8128. And these numbers alwaj^s end alternately in 6 and 8.

Munyos^ stated that Boethius added to EucUd's idea of perfect number
that of deficient (diminute) and abundant (redundantem) numbers.

Isidorus of Seville^ (570-636) distinguished even and odd numbers,
perfect and abundant numbers, linear, flachen and Korper Zahlen (primes,
products of two, products of three factors).

Alcuin^ (735-804) , of York and Tours, explained the occurrence of the
number 6 in the creation of the universe on the ground that 6 is a perfect
number. The second origin of the human race arose from the deficient
number 8; indeed, in Noah's ark there were 8 souls from which sprung the
entire human race, showing that the second origin was more imperfect than
the first, which was made according to the number 6.

^lamblichus Chalcidensis ex Coele-Syria in Nicomachi Geraseni arithmeticam introduc-

tionem, et de Fato. Accedit Joachimi Camerarii explicatio in duos libros Nicomachi.

Ed., Samuel Tennulius. Amhemiae, 1668, pp. 43-47. (Greek text and Latin translation

in parallel columns.)
lamblichi in Nicomachi arithmeticam introductionem Uber ad fidem codicis Florentini.

Ed., H. Pistelli. Lipsiae, 1894. (Greek.)
*De Civitate Dei, hber XI, cap. XXX, ed., B. Dombart, Lipsiae, 1877, 1, p. 504. The reference

by Frizzo"' i' to lib. II, cap. 39.
"Arithmetica boetij, Augsburg, 1488; Cologne, 1489; Leipzig, 1490; Venice, 1491-2, 1499;

Paris, [1496, 1501], 1503, etc.; lib. 1, cap. 20. "De generatione numeri perfecti."
Opera Boetii, Venice, 1491-2, etc.; ed., Friedlein, Leipzig, 1867.
"Institvtiones arithmeticae ad percipiendam astrologiam et mathematicas facultates neces-

sariae. Auctore Hieronymo Mimj'os, Valentiae, 1566, f. 5, verso.
*Incipit epistola Isidori iunioris hispalensis . . . Finit Uber etymologiarum . . . [Augsburg,

1472]; Venice, 1483, etc. In this book of etymologies, arithmetic is treated very briefly

in Book 3, beginning f . 15.
•Bibhotheca Rerum Germanicarum, tomus sextus: Monumenta Alcuiniana, Berlin, 1873,

epistolae 259, pp. 818-821. Cf. Migne, Patrologiae, vol. 100, 1851, p. 665; Hankel,

Geschichte Math., p. 311.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 5

Thabit ben Korrah,^° in a manuscript composed the last half of the
ninth century, attributed to Pythagoras and his school the employment of
perfect and amicable numbers in illustration of their philosophy. Let
s = 1+2+ ... +2". Then (prop. 5), 2'*s is a perfect number if s is a prime;
2"p is abundant if p is a prime <s, deficient if p is a prime >s, and the
excess or deficiency of the sum of all the divisors over the number equals
the difference of s and p. Let (prop. 6) p' and p" be distinct primes >2;
the sum of the divisors <N oi N = p'p"2" is

a = (2"+i-l)(l+p'+p") + (2"-l)py.

Hence N is abundant or deficient according as

a-iV=(2"+^-l)(l+p'+p")-py>0or <0.

Hrotsvitha,^^ a nun in Saxony, in the second half of the tenth century,
mentioned the perfect numbers 6, 28, 496, 8128.

Abraham Ibn Ezra^^" (tll67), in his commentary to the Pentateuch,
Ex. 3, 15, stated that there is only one perfect number between any two
successive powers of 10.

Rabbi Josef b. Jehuda Ankin^^'', at the end of the twelfth century, recom-
mended the study of perfect numbers in the program of education laid out
in his book "Healing of Souls."

Jordanus Nemorarius^^ (tl236) stated (in Book VII, props. 55, 56) that
every multiple of a perfect or abundant number is abundant, and every
divisor of a perfect number is deficient. He attempted to prove (VII, 57)
the erroneous statement that all abundant numbers are even.

Leonardo Pisano, or Fibonacci, cited in his Liber Abbaci^^ of 1202,
revised about 1228, the perfect numbers

1 2^(2^-1) =6, i 2^(2^-1) =28, | 2^(2^-1) =496,

excluding the exponent 4 since 2^ — 1 is not prime. He stated that by pro-
ceeding so, you can find an infinitude of perfect numbers.

i^Manuscript 952, 2, Suppl. Arabe, Bibliotheque imperiale, Paris. Textual transl., except
of the proofs which are given in modem algebraic notation as foot-notes [as numbers
were represented by line, in the manuscript], by Franz Woepcke, Journal Asiatique,
(4), 20, 1852, 420-9.

"See Ch. Magnin, Theatre de Hrotsvitha, Paris, 1845.

""Mikrooth Gedoloth, Warsaw, 1874 ("Large Bible" in Hebrew). Samuel Ben Sdadias Ibn
Motot; a Spaniard, wrote in 1370 a commentary on Ibn Ezra's commentary, Perush ai
Perush Ibn Ezra, Venice, 1554, p. 19, noting the perfect numbers 6, 28, 496, 8128, and
citing EucUd's rule. Steinschneider, in his book on Ibn Ezra, Abh. Geschichte Math.
Wiss., 1880, p. 92, stated that Ibn Ezra gave a rule for finding all perfect numbers.
As this rule is not given in the Mikrooth Gedoloth of 1874, Mr. Ginsburg of Columbia
University infers the existence of a fuller version of Ibn Ezra's commentary.
"^Quoted by Giideman, Das Jiidische Unterrichtswesen wahrend der Spanish Arabischen
Periode, Wien, 1873.

*^In hoc opere contenta. Arithmetica decern libris demonstrata .... Epitome i libros
arithmeticos diui Seuerini Boetij . . . , Paris, 1496, 1503, etc. It contains Jordanus'
"Elementa arithmetica decern libris, demonstrationibus Jacobi Fabri Stapulensis," and
"Jacobi Fabri Stapulenais epitome in duos Hbros arithmeticos diui Seuerini Boetij."

i^Il Liber Abbaci di Leonardo Pisano. Roma, 1857, p. 283 (Scritti, vol. 1).

6 History of the Theory of Numbers. [Chap. I

In the manuscripts^ Codex lat. Monac. 14908, a part dated 1456 and a
part 1461, the first four perfect numbers are given (J. 33') as usual and the
fifth perfect number is stated correctly to be 33550336.

Nicolas Chuquet^^ defined perfect, deficient, and abundant numbers,
indicated a proof of EucHd's rule and stated incorrectly that perfect num-
bers end alternately in 6 and 8.

Luca Paciuolo, de Borgo San Sepolcro,^^ gave (f. 6) Euclid's rule, saying
one must find by experiment whether or not the factor 1+2+4+. . . is
prime, stated (f. 7) that the perfect numbers end alternately in 6 and 8, as
6, 28, 496, etc., to mfinity. In the fifth article (ff. 7, 8), he illustrated the
finding of the aliquot divisors of a perfect number by taking the case of the
fourteenth perfect number 9007199187632128. He gave its half, then the
half of the quotient, etc., until after 26 divisions by 2, the odd number
134217727, marked " Indi^dsibilis " [prime]. Dividing the initial number
by these quotients, he obtained further factors [1,2,..., 2'^, but written at
length]. The proposed number is said to be evidently perfect, since it is the
sum of these factors [but he has not employed all the factors, since the above
odd number equals 2'-'^ — 1 and has the factor 2^ — 1 = 7] . Although Paciuolo
did not list the perfect numbers between 8128 and 90 . . .8, the fact that he
called the latter the fourteenth perfect number imphes the error expressly
committed bj^ Bo^illus.^"

Thomas Bradwardin^" (1290-1349) stated that there is only one perfect
number (6) between 1 and 10, one (28) up to 100, 496 up to 1000, 8128 up
to 10000, from which these numbers, taken in order, end alternately in 6
and 8. He then gave EucUd's rule.

Faber Stapulensis^^ or Jacques Lefevre (born at Etaples 1455, tl537)
stated that all perfect numbers end alternately in 6 and 8, and that Euclid's
rule gives all perfect numbers.

Georgius Valla^^ gave the first four perfect numbers and observed that

"The manuscript is briefly described by Gerhardt, Monatsber. Berlin Ak., 1870, 141-2.

See Catalogus codicum latinorum bibliothecae regiae Monacensis, Tomi II, pars II,

codices nuna. 11001-15028 complectus, Munich, 1876, p. 250. An extract of ff. 32-34

on perfect numbers was published by MaximiUan Curtze, BibUotheca Mathematica,

(2), 9, 1895, 39-42.
"Triparty en la science des nombres, manuscript No. 1436, Fonds Fran^ais, BibliothSque

Nationale de Paris, written at Lyons. 1484. Published by Aristide Marre, Bull. Bibl.

Storia Sc. Mat. et Fis.. 13 (1880), 593-659, 693-814; 14 (1881), 417-460. See Part 1,

Ch. Ill, 3, 619-621, manuscript, ff. 20-21.
"Summa de Arithmetica geometria proportioni et proportionalita. [Suma . . , Venice, 1494.]

Toscolano, 1523 (two editions substantially the same).
"Arithmetica thome brauardini. Tractatus perutilis. In arithmetica speculativa a magistro

thoma Brauardini ex libris eucUdis boecij & ahorum qua optimne excerptus. Parisiis,

1495, 7th unnumbered page.
Arithmetica Speculativa Thome Brauardini nuper mendis Plusculis tersa et diligenter Impressa,

Parisiis [1502], 6th and 7th unnumbered pages. Also undated edition [1510], 3d page.
"Epitome (iii) of the arithmetic of Boethius in Faber's edition of Jordanus," 1496, etc.

Also in Introductio Jacobi fabri Stapulesis in Arithmecam diui Seuerini Boetij pariter

Jordani, Paris, 1503, 1507. Also in Stapulensis, Jacobi Fabri, Arithmetica Boethi

epitome, Basileae, 1553, 40.
"De expetendis et fvgiendis rebvs opvs, Aldus, 1501. Liber I ( = Arithmeticae I), Cap. 12.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NuMBERS. 7

"these happen to end in 6 or 8. . .and these terminal numbers will always
be found alternately."

Carolus Bovillus^" or Charles de Bouvelles (1470-1553) stated that every
perfect number is even, but his proof applies only to those of Euclid's type.
He corrected the statement of Jordanus^^ that every abundant number is
even, by citing 45045 [ = 5-9-7-ll-13] and its multiples. He stated that
2" — 1 is a prime if n is odd, expUcitly citing 511 [ = 7-73] as a prime. He
listed as perfect numbers 2"~^(2'* — 1), n ranging over all the odd numbers
^ 39 [Cataldi^ later indicated that 8 of these are not perfect]. He repeated
the error that all perfect numbers end alternately in 6 and 8. He stated
(f. 175, No. 25) that if the sum of the digits of a perfect number >6 be
divided by 9, the remainder is unity [proved for perfect numbers of Euclid's
type by Cataldi,^^ p. 43]. He noted (f. 178) that any divisor of a perfect
number is deficient, any multiple abundant. He stated (No. 29) that one or
both of 6n=i=l are primes and (No. 30) conversely any prime is of the form
6n=t 1 [Cataldi,^ p. 45, corrects the first statement and proves the second].
He stated (f. 174) that every perfect number is triangular, being 2" (2'' — l)/2.

Martinus^^ gave the first four perfect numbers and remarked that they
end alternately in 6 and 8.

Gasper Lax'^^ stated that the perfect numbers end alternately in 6 and 8.

V. Rodulphus Spoletanus^^ was cited by Cataldi,'*^ with the implication
of errors on perfect numbers. [Copy not seen.]

Girardus Ruffus^^ stated that every perfect number is even, that most
odd numbers are deficient, that, contrary to Jordanus,^^ the odd number
45045 is abundant, and that for n odd 2^* — 1 always leads to a perfect num-
ber, citing 7, 31, 127, 511, 2047, 8191 as primes [the fourth and fifth are
composite].

Feliciano^^ stated that all perfect numbers end alternately in 6 and 8.

Regius^^ defined a perfect number to be an even number equal to the
sum of its aliquot divisors, indicated that 511 and 2047 are composite, gave
correctly 33550336 as the fifth perfect number, but said the perfect numbers

^''Caroli Bouilli Samarobrini Liber De Perfectis Numeris (dated 1509 at end), one (ff. 172-180)
of 13 tracts in his work, Que hoc volumine continetur: Liber de intellectu, . . . De
Numeris Perfectis, . . . , dated on last page, 1510, Paris, ex ofEcina Henrici Stephani.
Biography in G. Maupin, Opinions et Curiosit^s touchant la Math., Paris, 1, 1901, 186-94.

"Ars Arithmetica loannis Martini, Silicei: in theoricen & praxim. 1513, 1514. Arithmetica
loannis Martini, Scilicei, Paris, 1519.

"Arithmetica speculatiua magistri Gasparis Lax. Paris, 1515, Liber VII, No. 87 (end).

*3De proportione proportionvm dispvtatio, Rome, 1515.

"Divi Severini Boetii Arithmetica, dvobvs discreta hbris, Paris, 1521; ff. 40-44 of the commen-
tary by G. Ruffus.

"Libro di Arithmetica & Geometria speculatiua & praticale: Composto per maestro Fran-
cesco FeUciano da Lazisio Veronese Intitulato Scala Grimaldelli: Nouamente stampato.
Venice, 1526 (p. 3), 1527, 1536 (p. 4), 1545, 1550, 1560, 1570, 1669, Padoua, 1629, Verona,
1563, 1602.

*Vtrivsqve Arithmetices, epitome ex uariis authoribus concinnata per Hvdalrichum Regium.
Strasburg, 1536. Lib. I, Cap. VI: De Perfecto. Hvdalrichvs Regius, Vtrivsque. . .
ex variis . . . , Friburgi, 1550 [and 1543], Cap. VI, fol. 17-18.

8 History of the Theory of Numbers. [Chap. I

end alternately in 6 and 8. A multiple of an abundant or perfect number
is abundant, a divisor of a perfect number is deficient.

Cardan^^ (1501-1576) stated that perfect numbers were to be formed
by Euclid's rule and always end with 6 or 8; and that there is one between
any two successive powers of ten.

De la Roche-^ stated in effect that 2""^ (2" — 1) is perfect for every odd n,
citing in particular 130816 and 2096128, given by n = 9, n = ll. This
erroneous law led him to believe that the successive perfect numbers end
alternately in 6 and 8.

Noviomagus-^ or Neomagus or Jan Bronckhorst (1494-1570) gave
Euclid's rule correctly and stated that among the first 10 numbers, 6 alone is
perfect, . . . , among the first 10000 numbers, 6, 28,496, 8128 alone are perfect,
etc., etc. [implying falsely that there is one and but one perfect number
with any prescribed number of digits]. In Lib. II, Cap. IV, is given the
sieve (or crib) of Eratosthenes, with a separate column for the multiples
of 3, a separate one for the multiples of 5, etc.

WilUchius^'^ (tl552) listed the first four perfect numbers and stated that
to these are to be added a very few others, whose nature is that they end
either in 6 or 8.

Michael StifeP^ (1487-1567) stated that all perfect numbers except 6
are multiples of 4, while 4(8-1), 16(32-1), 64(128-1), 256(512-1), etc.,
to infinity, are perfect [error, Kraft^°]. He later^- repeated the latter error,
listing as perfect

2X3, 4X7, 16X31, 64X127, 256X511, 1024X2047,

"& so fort an ohn end." Every perfect munber is triangular.

Peletier^^ (1517-1582) stated (1549, V left; 1554, p. 20) that the perfect
numbers end in 6 or 8, that there is a single perfect number between any
two successive powers of 10, and (1549, C III left; 1554, pp. 270-1) that
4(8-1), 16(32-1), 64(128-1), 256(511),. . .are perfect. The first two
statements were also given later by Peletier.^

^'Hieronimi C. Cardani Medici Mediolanensis, Practica Arithmetice, & Mensurandi singu-

laris. Milan, 1537, 1539; Xiirnberg, 1541, 1542, Cap. 42, de proprietatibus numerorum

mirificis. Opera IV, Lyon, 1663.
-*Larismetique & Geometrie de maistre Estienne de la Roche diet Ville Franche, Nouuelle-

ment Imprimee & des fautea corrigee, Lyon, 1538, fol. 2, verso. Ed. 1, 1520.
'"De Nvmeris libri dvo .... authore loanne Nouiomago, Paris, 1539, Lib. II, Cap. III.

Reprinted, Cologne, 1544; Deventer, 1551. Edition by G. Frizzo, Verona, 1901, p. 132.
'°Iodoci Vvillichii Reselliani, Arithmeticae libri tres, Argentorati, 1540, p. 37.
'^Arithmetica Integra, Norimbergae, 1544, ff. 10, 11.
"Die Cosa Cbristoffs Rudolffs Die schonen Exempeln der Coss Durch Michael Stifel Gebessert

vnd sehr gemehrt, Konigsperg in Preussen, 1553, Anbang Cap. I, f. 10 verso, f. 11 (f.

27 v.), and 1571.
"L'Arithmetiqve de lacqves Peletier dv Mans, departie en quatre Liures, Poitiers, 1549,

1550, 1553. . . . , ff. 77 v, 78 r. Reviie e augmentee par 1' Auteur, Lion, 1554

Troisieme edition, reucue et augmentee, par lean de Tovmes, 1607.
"Arithmeticae Practicae methodvs facilis, per Gemmam Frisivm, Medicvm, ac Mathematicum

conscripta .... In eandem loannis Steinii & lacobi Peletarii Annotationes. Antver-

piae, 1581, p. 10.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 9

Postello^^ stated erroneously that 130816 [ = 256-511] is perfect.

Lodoico Baeza^^ stated that Euchd's rule gives all perfect numbers.

Pierre Forcadel" (tl574) gave 130816 as the fifth perfect number,
implying incorrectly that 511 is a prime.

Tartaglia^^ (1506-1559) gave an erroneous [Kraft ^^J list of the first
twenty perfect numbers, viz., the expanded forms of 2"~^(2'* — 1), for n = 2
and the successive odd numbers as far as n = 39. He stated that the sums
1+2+4, 1+2+4+8, .. .are alternately prime and composite; and that
the perfect numbers end alternately in 6 and 8. The third ''notable prop-
erty" mentioned is that any perfect number except 6 yields the remainder 1
when divided by 9.

Robert Recorde^^ (about 1510-1558) stated that all the perfect numbers
under 6-10^ are 6, 28, 496, 8128, 130816, 2096128, 33550336, 536854528 [the
fifth, sixth, eighth of these are not perfect].

Petrus Ramus^° (1515-1572) stated that in no interval between succes-
sive powers of 10 can you find more than one perfect number, while in many
intervals you will find none. At the end of Book I (p. 29) of his Arith-
meticae libri tres, Paris, 1555, Ramus had stated that 6, 28, 496, 8128 are
the only perfect numbers less than lOOpOO.

Franciscus Maurolycus*^ (1494-1575) gave an argument to show that
every perfect number is hexagonal and hence triangular.

Peter Bungus^^ (fieoi) gave (1584, pars altera, p. 68) a table of 20
numbers stated erroneously to be the perfect numbers with 24 or fewer
digits [the same numbers had been given by Tartaglia^^]. In the editions
of 1591, etc., p. 468, the table is extended to include a perfect number of
25 digits, one of 26, one of 27, and one of 28. He stated (1584, pp. 70-71 ;
1591, pp. 471-2) that all perfect numbers end alternately in 6 and 28;
employing Euclid's formula, he observed that the product of a power of 2
ending in 4 by a number ending in 7 itself ends in 28, while the product of
one ending in 6 by one ending in 1 ends in 6. He verified (1585, pars

^"Theoricae Arithmetices Compendium h Guilielmo Postello, Lutetiae, 1552, a syllabus on one

large sheet of arithmetic definitions.
"Nvmerandi Doctrina, Lvtetiae, 1555, fol. 27-28.

''L'Arithmeticqve de P. Forcadel de Beziers, Paris, 1556-7. Livre I (1556), fol. 12 verso.
3*La seconda Parte del General Trattato di Nvmeri, et Misvre di Nicolo Tartagha, Vinegia,

1556, f. 146 verso.
L' Arithmetiqve de Nicolas Tartagha Brescian .... Recueillie, & traduite d'ltalien en

FranQois, par Gvillavme Gosselin de Caen, .... Paris, 1578, f. 98 verso, f. 99.
'®The Whetstone of witte, whiche is the seconde parte of Arithmetike, London, 1557, eighth

unnumbered page.
^''Petri Rami Scholarum Mathematicarum, Libri unus et triginta, k Lazaro Schonero recog-

niti & emendati, Francofvrti, 1599, Libr. IV (Arith.), p. 127, and Basel, 1578.
"Arithmeticorvm hbri dvo, Venetiis, 1575, p. 10; 1580. Published with separate paging, at

end of Opuscula mathematica.
*^Mysticae nvmerorvm significationis liber in dvas divisvs partes, R. D. Petro Bongo Canonico

Bergomate avctore. Bergomi. Pars prior, 1583, 1585. Pars altera, 1584.
Petri Bungi Bergomatis Numerorum mysteria, Bergomi, 1591, 1599, 1614, Lutetiae Parisio-

rum, 1618, all four with the same text and paging. Classical and biblical citations on

numbers (400 pages on 1, 2, . . , 12). On the 1618 edition, see Font^s, M6m. Acad. So.

Toulouse, (9), 5, 1893, 371-380.

10 History of the Theory of Numbers. [Chap, i

prior, p. 238; 1591, p. 343) for the first seven numbers of his table [two
being imperfect, however] that the sum of the digits of a perfect number
exceeds by unity a multiple of 9. Every perfect number is triangular
(1591, p. 270). Every multiple of a perfect number is abundant, every
divisor deficient (1591, p. 464).

Unicornus^^ (1523-1610) cited Bungus and repeated his error that
2"- 1 (2^ — 1) is always perfect for n odd and that all perfect numbers end
alternately in 6 and 8.

Cataldi"^ (1548-1626) noted in his Preface that Paciuolo's^^ fourteenth per-
fect number 90. . .8 is in fact abundant since it arose from 1+2+4+ • ■ •
+2^^ = 134217727, which is divisible by 7,whereas Paciuolo said it was prime.
Citing the error of the latter, Bovillus,^° and others, that all perfect num-
bers end alternately in 6 and 8, Cataldi observed (p. 42) that the fifth per-
fect number is 33550336 and the sixth is 8589869056, from 8191 =2'^- 1 and
131071=2^^ — 1, respectively, proved to be primes (pp. 12-17) by actually
trying as possible divisor every prime less than their respective square roots.
He gave (pp. 17-22) the corresponding work showing 2^^ — 1 to be prime. He
stated (p. 11) that 2'*-! is a prime forn = 2, 3, 5, 7, 13, 17, 19, 23, 29, 31, 37,
remarking that the prime n = ll does not yield a perfect number since
(p. 5) 2^^ — 1=2047 = 23*89, while it is composite if n is composite. He
proved (p. 8) that the perfect numbers given by Euclid's rule end in 6 or 8.
He gave (pp. 28-40, 48) a table of all divisors of all even and odd numbers
^ 800, and a table of primes < 750.

Georgius Henischiib^^ (1549-1618) stated that the perfect numbers end
alternately in 6 and 8, and that one occurs between any two successive
powers of 10. He applied Euclid's formula without restricting the factor
2"—! to primes.

Johan Rudolff von Graff enried"*^ stated that all perfect numbers are
given by Euclid's rule, which he applied without restricting 2" — 1 to primes,
expressly citing 256X511 as the fifth perfect number. Every perfect
number is triangular.

Bachet de Mezirac''^ (1581-1638) gave (f. 102) a lengthy proof of
Euclid's theorem that 2'*p is perfect if p = l+2+ . . . +2^* is a prime, but

"De I'arithmetica vniversale del Sig. loseppo Vnicorno, Venetia, 1598, f. 57.

"Trattato de nvmeri perfetti di Pierto Antonio Cataldo, Bologna, 16C3. According to the
Preface, this work was composed in 1588. Cataldi founded at Bologna the Academia
Erigende, the most ancient known academy of mathematics; his interest in perfect
numbers from early youth is shown by the end of the first of his "due lettioni fatte nell'
Academia di Perugia" (G. Libri, Hist. Sc. Math, en ItaUe, 2d ed., vol. 4, Halle, 1865, p.
91). G. Wertheim, BibHotheca Math., (3), 3, 1902, 76-83, gave a summary of the Trattato.

"Arithmetica Perfecta et Demonstrata, Georgii Henischiib, Augsburg [1605], 1609, pp. 63-64.

"Arithmeticae Logistica Popularis Librii IIII. Jn welchen der Algorithmus in gantzen Zahlen
u. Fracturen . . . . , Bern, 1618, 1619, pp. 236-7.

*^Elementorum arithmeticorum libri XIII auctori D . . . , a Latin manuscript in the Biblio-
thfeque de I'lnstitut de France. On the inside of the front cover is a comment on the
sale of the manuscript by the son of Bachet to DaUbert, treasurer of France. A general
account of the contents of the manuscript was given by Henry, Bull. Bibl. Storia Sc. Mat.
e Fis., 12, 1879, pp. 619-641. The present detailed account of Book 4, on perfect numbers,
was taken from the manuscript.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AMICABLE NUMBERS. 11

(f. 103, verso) is abundant if p is composite. Every multiple of a perfect
or abundant number is abundant, every divisor of a perfect number is
deficient (ff. 104 verso, 105). The product of two primes, other than 2X3,
is deficient (f. 105 verso). The odd number 945 is abundant, the sum of its
ahquot divisors being 975 (f. 107). Commenting (f. Ill verso, f. 112) on
the statement of Boethius^ and Cardan^^ that the perfect numbers end
alternately in 6 and 8, he stated that the fourth is 8128 and the fifth is
2096128 [an error], the fifth not being 130816 = 256X511, since 511 =7X73.

Jean Leurechon^^ (about 1591-1670) stated that there are only ten
perfect numbers between 1 and 10^^, listed them (noting the admirable
property that they end alternately in 6 and 8) and gave the twentieth per-
fect number. [They are the same as in Tartaglia's^^ list.]

Lantz^^ stated that the perfect numbers are 2(4-1), 4(8-1), 16(32-1),
64(128-1), 256(512-1), 1024(2048-1), etc.

Hugo Sempilius^° or Semple (Scotland, 1594-Madrid, 1654) stated that
there are only seven perfect numbers up to 40,000,000; they end alternately
in 6 and 8.

Casper Ens^^ stated that there are only seven perfect numbers <4-10'',
viz., 6, 28, 496, 8128, 130816, 1996128 [for 2096128], 33550336, and that they
end alternately in 6 and 8.

Daniel Schwenter^^ (1585-1636) made the same error as Casper Ens.^^

Erycius Puteanus^^ quoted from Martiano Capella, lib. VII, De Nuptiis
Philologiae, to the effect that the perfect number 6 is attributed to Venus;
for it is made by the union of the two sexes, that is, from triad, which is
male since it is odd, and from diad, which is feminine since it is even.
Puteanus said that the perfect numbers in order are 6, 28, 496, 8128,
130816, 2096128, 33550336, and gave all their divisors [implying that 511,
2047, 8191 are primes], and stated that these seven and all the remaining
end alternately in 6 and 8. Between any two successive powers of 10 is one
perfect number. That they are all triangular adds perfection to the perfect.

Joannes Broscius^"^ or Brocki remarked that there is no perfect number
between 10000 and 10000000, contrary to Stifel,^^ Bungus,^^ Sempilius.^"
Puteanus,^^ and the author of Selectarum Propositionum Mathematicarum,
quas propugnavit, Mussiponti, Anno 1622, Maximilianus Willibaldus, Baro

^^Recreations math^matiques, Pont-^-Mousson, 1624; London, 1633, 1653, 1674 (these three
EngUsh editions by Wm. Oughtred), p. 92. The authorship is often attributed to
Leurechon's pupil Henry Van Etten, whose name is signed to the dedicatory epistle.
Cf. Poggendorff, Handworterbuch, 1863, 2, p. 250 (under C. Mydorge); Bibliotheque
des 6crivains de la compagnie de Jesus, par A. de Backer, 2, 1872, 731; Biograpliie
Generale, 31, 1872, 10.

"Institutionum Arithmeticarum hbri quatuor h loanne Lantz, Coloniae Agrippinae, 1630, p. 54.

"De Mathematicis Disciphnis hbri Duodecim, Antverpiae, 1635, Lib. 2, Cap. 3, N. 10, p. 46.
There is (pp. 263-5) an index of writers on geometry and one for arithmetic.

"Thaumaturgus Math., Munich, 1636, p. 101; Coloniae. 1636, 1651; Venice, 1706.

"Dehciae Physico-Mathematicae oder Mathemat: vnd Philosophische Erquickstunden,
part I (574 pp.), Numberg, 1636, p. 108.

"De Bissexto Liber: nova temporis facula qua intercalandi arcana .... Lovanii, 1637;
1640, pp. 103-7. Reproduced by J. G. Graevius, Thesaurus Antiquitatum Romanarum
(12 vols., 1694-9), Lugduni Batavorum, vol. 8.

12 History of the Theory of Numbers. [Chap, i

in Waldpurg. WTiile they considered 511X256 and 2047X1024 as perfect,
511 has the factor 7, and (as pointed out to him by Stanislaus Pudlowski)
2047 has the factor 23. Broscius stated that

2^-1 has the factor 3 5 7 11 13 17 19 23 29 31
if n is a multiple of 2 4 3 10 12 8 18 11 28 5.

The contents of the second dissertation are given below under the date 1652.

Ren^ Descartes,^^ in a letter to Mersenne, November 15, 1638, thought
he could prove that every even perfect number is of Euclid's type, and that
every odd perfect number must have the form ps^, where p is a prime. He
saw no reason why an odd perfect number may not exist. For p = 22021,
s = 3'7-ll-13, ps^ would be perfect if p were prime [but p = 61-19^]. In a
letter to Frenicle, January 9, 1639, Oeuvres, 2, p. 476, he expressed his belief
that an odd perfect number could be found by replacing 7, 11, 13 in s by
other values.

Fermat^^ stated that he possessed a method of solving all questions
relating to aliquot parts. Citing this remark, Frenicle^' challenged Fermat
to find a perfect number of 20 or 21 digits. Fermat^^ replied that there is
none with 20 or 21 digits, contrary to the opinion of those who believe
that there is a perfect number between any two consecutive powers of 10.

Fermat,^^ in a letter to Mersenne, June (?), 1640, stated three proposi-
tions which he had proved not without considerable trouble and which he
called the basis of the discovery of perfect numbers: if n is composite, 2" — 1
is composite; if n is a prime, 2" — 2 is divisible by 2n, and 2" — 1 is divisible
by no prime other than those of the form 2kn-\-l [cf . Euler^']. For example,
2"-l = 23-89, 2^^-l has the factor 223. Also 2"^^-! has the factor 47,
Oeuvres, 2, p. 210, lett-er to Frenicle, October 18, 1640.

Mersenne^° (1588-1648) stated that, of the 28 numbers* exhibited by

"De numeris perfectis disceptatio qua ostenditur a decern millibus ad centies centena millia,
nullum esse perfectum numenim atque ideo ab unitate usque ad centies centena millia
quatuor tantum perfectos numerari, Amsterdam, 1638. Reproduced as the first (pp.
115-120) of two dissertations on perfect numbers, they forming pp. 111-174 of Apologia
pro Aristotele & Evchde, contra Petrvm Ramvm, & aUos. Addititiae sunt Dvae Discep-
tationes de Nvmeris Perfectis. Authore loanne Broscio, Dantiaci, 1652 (with a some-
what different title, Amsterdam, 1699).

"Oeuvres de Descartes, II, Paris, 1898, p. 429.

s«Oeuvres de Fermat, 2, Paris, 1894, p. 176; letter to Mersenne, Dec. 26, 1638.

*'Oeuvres de Fermat, 2, p. 185; letter to Mersenne, March, 1640.

osQeuvres, 2, p. 194; letter to Mersenne, May (?), 1640.

"Oeuvres de Fermat, 2, pp. 198-9; Varia Opera Math. d. Petri de Fermat, Tolosae, 1679, p.
177; Precis des Oeuvres math, de P. Fermat et de 1' Arithmdtique de Diophante, par E.
Brassinne, M6m. Ac. Imp. Sc. Toulouse, (4), 3, 1853, 149-150.

•°F. Marini Mersenni minimi Cogitata Physico Mathematica, Parisiis, 1644. Praefatio
Generahs, No. 19. C. Henry (Bull. Bibl. Storia Sc. Mat. e Fis., 12, 1879, 524-6) beheved
that these remarks were taken from letters from Fermat and Frenicle, and that Mersenne
had no proof. A similar opinion was expressed by W. W. Rouse Ball, Messenger
Math., 21, 1892, 39 (121). On documents relating to Mersenne see Tinterm^diaire des
math., 2, 1895, 6; 8, 1901, 105; 9, 1902, 101, 297; 10, 1903, 184. Cf. Lucas."*

*Only 24 were given by Bungus. While his table has 28 lines, one for each number of digits,
there are no entry of numbers of 5, 11, 17, 23 digits.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AMICABLE NUMBERS. 13

Bungus,^^ chap. 28, as perfect numbers, 20 are imperfect and only 8 are
perfect :

6, 28, 496, 8128, 23550336 [for 33. . .], 8589869056,
137,438691328, 2305843008139952128,

which occur at the lines marked 1, 2, 3, 4, 8, 10, 12 and 29 [for 19] of
Bungus' table [indicating the number of digits]. Perfect numbers are so
rare that only eleven are known, that is, three different from those of
Bungus; norf is there any perfect number other than those eight, unless
you should surpass the exponent 62 in 1+2+2^+ .. . The ninth perfect
number is the power with the exponent 68 less 1; the tenth, the power 128
less 1 ; the eleventh, the power 258 less l,i.e., the power 257, decreased by
unity, multiplied by the power 256. [The first 11 perfect numbers are
thus said to be 2"-'(2"-l) for n = 2, 3, 5, 7, 13, 17, 19, 31, 67, 127, 257, in
error as to n = 61, 67, 89, 107 at least.] He who would find 11 others will
know that all analysis up to the present will have been exceeded, and will
remember in the meantime that there is no perfect number from the power
17000 to 32000, and no interval of powers can be assigned so great but
that it can be given without perfect numbers. For example, if the exponent
be 1050000, there is no larger exponent n up to 2090000 for which 2" — 1
is a prime. One of the greatest difficulties in mathematics is to exhibit a
prescribed number of perfect numbers; and to tell if a given number of
15 or 20 digits is prime or not, all time would not suffice for the test, what-
ever use is made of what is already known.

Mersenne" stated that 2^ — 1 is a prime if p is a prime which exceeds
by 3, or by a smaller number, a power of 2 with an even exponent. Thus
2^-1 is a prime since 7 = 2^3; again, since 67 = 3+2*^, 2^^ + 1 = 1... 7
[for 2®^ — 1] is a prime and leads to a perfect number [error corrected by
Cole^^^]. Understand this only of primes 2^ — 1. Wherefore this property
does not belong to the prime 5, but to 3, 7, 31, 127, 8191, 131071, 524287,
2147483647, and all such. Numbers expressible as the sum or difference
of two squares in several ways are composite, as 65 = 1+64 = 16+49. As
he speaks of Frenicle's knowledge of numbers, at least part of his results
are doubtless due to the latter.

In 1652, J. Broscius (Apologia,^^ p. 121) observed that while perfect
numbers were deduced by Euclid from geometrical progressions, they may
be derived from arithmetical progressions:

6 = 1+2+3, 28 = 1+2+3+4+5+6+7, 496 = 1+2+3+ ... +31.

fNeque enim vllus est alius perfectus ab illis octo, nisi superes exponentem numerum 62,
progressionis duplae ab 1 incipientis. Nonus enim perfectus est potestas exponentis 68,
minus 1. Decimus, potestas exponentis 128, minus 1. Vndecimus denique, potestas
258, minus 1, hoc est potestas 257, unitate decurtata, multiplicata per potestatem 256.

*T. Marini Mersenni Novarvm Observationvm Physico-Mathematicarum^ Tomvs III, Parisiis,
1647, Cap. 21, p. 182. The Reflectiones Physico-Math. begin with p. 63; Cap. 21 is
quoted in Oeuvres de Fennat, 4, 1912, pp. 67-8.

14 History of the Theory of Numbers. [Chap, i

He stated that while perfect numbers end with 6 or 28, the proof by Bungus*'
does not show that they end alternately with 6 and 28, since Bungus
included imperfect as well as perfect numbers. The numbers 130816 and
2096128, cited as perfect by Puteanus,^^ are abundant. After giving a
table of the expanded form of 2" forn = 0, 1, . . . , 100, Broscius (p. 130, seq.)
gave a table of the prime divisors of 2" — 1 (n = 1, . . . , 100), but showing no
prime factor when n is any one of the primes, other than 11 and 23, less
than 100. For n = ll, the factors are 23, 89; for n = 23, the factor 47 is
given. Thus omitting unity, there remain only 23 numbers out of the first
hundred which can possibly generate perfect numbers. Contrary to Car-
dan,^^ but in accord with Bungus,^^ there is (p. 135) no perfect number
between 10* and 10\ Of Bungus' 24 numbers, only 10 are perfect (pp.
135-140): those with 1, 2, 3, 4, 8, 10, 12, 18, 19, 22 digits, and given by
2'-i(2'*-l) for n = 2, 3, 5, 7, 13, 17, 19, 29, 31, 37, respectively. The pri-
maUty of the last three was taken on the authority of unnamed predecessors.

There are only 21 abundant numbers between 10 and 100, and all of
them are even; the only odd abundant number <1000 is 945, the sum of
whose aliquot di\isors is 975 (p. 146). The statement by Lucas, Th^orie
des nombres, 1, Paris, 1891, p. 380, Ex. 5, that 3^-5-79 [deficient] is the
smallest abundant number is probably a misprint for 945 = 3^-5-7. This
error is repeated in Encyclopedic Sc. Math., I, 3, Fas. 1, p. 56.

Johann Jacob Heinlin^- (1588-1660) stated that the only perfect num-
bers <4-10' are 6, 28, 496, 8128, 130816, 2096128, 33550336, and that all
perfect numbers end alternately in 6 and 8.

Andrea Tacquet^^ (Antwerp, 1612-1660) stated (p. 86) that Euclid's
rule gives all perfect numbers. Referring to the 11 numbers given as
perfect by Mersenne,^^ Tacquet said that the reason why not more have
been found so far is the greatness of the numbers 2^ — 1 and the vast labor
of testing their primaUty.

Frenicle^ stated in 1657 that EucUd's formula gives all the even perfect
numbers, and that the odd perfect numbers, if such exist, are of the form
p/c^, where p is a prime of the form 4n+l [cf. Euler^^].

Frans van Schooten^^ (the younger, 1615-1660) proposed to Fermat
that he prove or disprove the existence of perfect numbers not of Euclid's
type.

Joh. A. Leuneschlos^^ remarked that the infinite multitude of numbers
contains only ten perfect numbers; he who will find ten others will know

'*Joh. Jacobi Heinlini, Synopsis Math, praecipuas totius math .... Tubmgae, 1653. Synopsis

Math. Universalis, ed. Ill, Tubingae, 1679, p. 6. English translation of last by Venterus

Mandey, London, 1709, p. 5.
"Arithmeticae Theoria et Praxis, Lovanii, 1656 and 1682 (same paging), [1664, 1704]. Hia

opera math., Antwerpiae, 1669, does not contain the Arithmetic.
"Correspondence of Chr. Huygens, No. 389; Oeuvres de Fermat, 3, Paris, 1896, p. 567.
"Oeuvres de Huygens, II, Correspondence, No. 378, letter from Schooten to J. Wallis, Mar. 18,

1658. Oeuvres de Fermat, 3, Paris, 1896, p. 558.
"Mille de Quantitate Paradoxa Sive Admiranda, Heildelbergae, 1658, p. 11, XLVI, XLVII.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 15

that he has surpassed all analysis up to the present. Goldbach" called
Euler's attention to these remarks and stated that they were probably
taken from Mersenne, the true sense not being followed.

Wm. Leybourn^^ hsted as the first ten perfect numbers and the twentieth
those which occur in the table of Bungus.^^ "The number 6 hath an emi-
nent Property, for his parts are equal to himself."

Samuel Tennulius, in his notes (pp. 130-1) on lamblicus,^ 1668, stated
that the perfect numbers end alternately in 6 and 8, and included 130816 =
256-511 and 2096128 = 1024-2047 among the perfect numbers.

Tassius®^ stated that all perfect numbers end in 6 or 8. Any multiple
of a perfect or abundant number is abundant, any divisor of a perfect
number is deficient. He gave as the first eight known perfect numbers the
first eight listed by Mersenne.^"

Joh. Wilh. Pauli^° (Philiatrus) noted that if 2" — 1 is a prime, n is, but
not conversely. For n = 2, 3, 5, 7, 13, 17, 19, 2"-l is a prime; but 2^^-l
is divisible by 23, 2^^ — 1 by 47, and 2*^ — 1 by 83, the three divisors being
2n+l.

G. W. Leibniz'^^ quoted in 1679 the facts stated by Pauli and set himself
the problem to find the basis of these facts. Returning about five years
later to the subject of perfect numbers, Leibniz implied incorrectly that
2^^ — 1 is a prime if and only if p is.

Jean Prestet^^ (tl690) stated that the fifth, . . . , ninth perfect numbers are

23550336 [for 33. . .], 8589869056, 137438691328, 238584300813952128 [for

2305. . .39952128], 2''^-2^'\

[Hence 2'*-^(2'*-l) for 7i = 13, 17, 19, 31, 257. The numerical errors were
noted by E. Lucas,i24 p 7g4 j

Jacques Ozanam^^ (1640-1717) stated that there is an infinitude of perfect
numbers and that all are given by Euclid's rule, which is to be applied only
when the odd factor is a prime.

Charles de Neuveglise^^ proved that the products 3-4, . . ., 8-9 of two
consecutive numbers are abundant. All multiples of 6 or an abundant
number are abundant.

"Correspondence Math. Phy8.,ed.,Fus8, 1, 1843; letters to Euler, Oct. 7, 1752 (p. 584), Nov. 18

(p. 593).
'^Arithmetical Recreations; or Enchriridion of Arithmetical Questions both Delightful and

Profitable, London, 1667, p. 143.
"Arithmeticae Empiricae Compendium, Johannis Adolfi Tassii. Ex recensione Henrici Siveri,

Hamburgi, 1673, pp. 13, 14.
^"De nvmiero perfecto, Leipzig, 1678, Magister-disputation.
"Manuscript in the Hannover Library. Cf. D. Mahnke, Bibhotheca Math., (3), 13, 1912-3,

53-4, 260.
"Nouveaux elemens des Mathematiques, ou Principes generaux de toutes les sciences, Paris,

1689, I, 154-5.
"Recreations mathematiques et physiques, Paris and Amsterdam, 2 vols., 1696, I, 14, 15.
"Traits methodique et abreg6 de toutes les mathematiques, Trevoux, 1700, tome 2 (L'arith-

m^tique ou Science des nombres), 241-8.

16 History of the Theory of Numbers. [Chap, i

John Harris,"^ D. D., F. R. S., stated that there are but ten perfect
numbers between unity and one million of millions.

John Hiir^ stated that there are only nine perfect numbers up to a
hundred thousand million. He gave (pp. 147-9) a table of values of 2"
forn = l,. . ., 144.

Christian Wolf" (1679-1754) discussed perfect numbers of the form
y"x [where x, y are primes]. The sum of its aliquot parts is

l+y+ . . . +i/"+a:+?/x+ . . . +i/""'x,
which must equal y'^x. Thus

x = {l-\-y+ . . . +2/")M d = y^-l-y- . . . -7/""^

He stated* that x is an integer only when d = l, and that this requires
y = 2, x = l +2+ . . . +2". Then if this x is a prime, 2"x is a perfect number.
This is said to be the case forn = 8 and n = 10, since 2^ — 1 = 51 1 and 2^' — 1 =
2047 are primes, errors pointed out bj^ Euler.^^ A. G. Kastner^^ was not
satisfied with the argument leading to the conclusion y = 2.
Jacques Ozanam^^ listed as perfect numbers

2(4-1), 4(8-1), 16(32-1), 64(128-1), 256(512-1), 1024(2048-1),. . .

without expUcit mention of the condition that the final factor shall be prime,
and stated that perfect numbers are rare, only ten being known, and all
end in 6 and 8 alternately. [Criticisms by Montucla,®^ Gruson.-^°°]

Johann Georg Liebnecht^° said there were scarcely 5 or 6 perfect num-
bers up to 4.10"; they always end alternately in 6 and 8.

Alexander ]Malcolm^^ observed that it is not yet proved that there is no
perfect number not in Euclid's set. He stated that, if pA is a perfect
number, where p is a prime, and if M<p and M is not a factor of A, then
MM is an abundant number [probably a misprint for MA, as the condi-
tions are satisfied when p = 7, .4=4, M = 5, and MA =20 is abundant, while
Af^ = 25 is deficient].

Christian Wolf^- made the same error as Casper Ens.^^

^'Lexicon Technicum, or an Universal English Dictionarj' of Arts and Sciences, vol. I, London,
1704; ed. 5, vol. 2, London, 1736.

"Arithmetik, London, ed. 2, 1716, p. 3.

^'Elementa Matheseos Universae, Halae Magdeburgicae, vol. I, 1730 and 1742, pp. 383-^, of
the five volume editions [first printed 1713-41]; vol. I, 1717, 315-6, of the two volume
edition. Quoted, with other errors, Ladies' Diary, 1733, Q. 166; Leybourn's ed., 1,
1817, 218; Button's ed., 2, 1775, 10; Diarian Repository, by Soc. Math., 1774, 289.

*"Jam ut X sit numerus integer, nee in casu speciali, si y per numerum explicetur, numerus
partium aliquotarum diversus sit a numero earundem in formula general!; necesse est ut
d = l."

"Math. Anfangsgrlinde, I, 2 (Fortsetzung der Rechnenkunst, ed. 2, 1801, 546-8).

"Recreations math., new ed. of 4 vols., 1723, 1724, 1735, etc., I, 29-30.

'"Grund-Satze der gesammten Math. Wiss. u. Lehren, Giessen u. Franckfurt, 1724, p. 21.

*iA new system of arithmetik, theoretical & practical, London, 1730, p. 394.

"Mathematisches Lexicon, I, 1734 (under Vollkommen Zahl).

Chap. Il PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 17

Leonard Euler^^ (1707-1783) noted that 2'' — 1 may be composite for n
a prime; for instance, 2^' — 1 = 23-89, contrary to Wolf.'^^ If n = 4m — 1
and 8m — 1 are primes, 2" — 1 has the factor 8m — 1, so that 2^-1 is com-
posite for n = ll, 23, 83, 131, 179, 191, 239, etc. [Proof by Lucas.^^sj
Furthermore, 2^^-l has the factor 223, 2^^-l the factor 431, 22^-1 the
factor 1103, 2"^ — 1 the factor 439, etc. ''However, I venture to assert
that aside from the cases noted, every prime less than 50, and indeed than
100, makes 2"~^(2" — 1) a perfect number, whence the eleven values 1, 2, 3,
5, 7, 13, 17, 19, 31, 41, 47 of n yield perfect numbers. I derived these
results from the elegant theorem, of whose truth I am certain, although I
have no proof: aJ^ — V is divisible by the prime n+1, if neither a nor h is."
[For later proofs by Euler, see Chapter III on Fermat's theorem.] Euler's
errors as to n = 41 and 47 were corrected by Winsheim,®^ Euler^^ himself,
and Plana.i^o

Michael Gottlieb Hansch^ stated that 2^*— 1 is a prime if n is any of
the twenty- two primes ^79 [error, Winsheim,^^ Kraft^^].

George Wolfgang Kraft^^ corrected Stifel's^^ error that 511-256 is per-
fect and the error of Ozanam (Elementis algebrae, p. 290) that the sum of
all the divisors of 2*" is a prime, by noting that the sum forn = 2 is 511 = 7-73 ;
and n6ted that false perfect numbers were listed by Ozanam.'^^ Kraft
presented (pp. 9-11) an incomplete proof, communicated to him by Tobias
Maier [cf. Fontana^^^], that every perfect number is of Euclid's type.
Let 1, m, n, . . .,p, A,. . .be the aliquot parts of any perfect number pA,
where p and A are the middle factors [as 4 and 7 jn 28]. Then

q r n m

Solving for A, he stated that the denominator must be unity, whence
'p = 2q/D, D = q — l—q/r — q/n — q/m. Again, D = l, whence g = 2r/D',
D' = r — l—r/n—r/m. From I>' = 1, r = 2n/I)", D" = n — l—n/m. From
D" = l, n = 2m/(m — 1), m — 1 = 1, m = 2, n = 4, r = 8, etc. Thus the aliquot
parts up to the middle must be the successive powers of 2, and A must be
a prime, since otherwise there would be new divisors. For p = 2"~\ we
get A =2" — 1. Kraft observed that if we drop from Tartaglia's^^ list of 20
numbers those shown to be imperfect by Euler's^^ results, we have left only
eight perfect numbers 2"-^(2"-l) for n^39, viz., those for n = 2, 3, 5, 7, 13,
17, 19, 31. For these, other than the first, as well as for the false ones of
Tartaglia, if we add the digits, then add the digits of that sum, etc., we
finally get unity (p. 14) [proof by WantzeP^^]. All perfect numbers end
in 6 or 28.

*3Comm. Acad. Petropol., 6, 1738, ad annos 1732-3, p. 103. Commentationes Arithmeticae

Collectae, I, Petropoli, 1849, p. 2.
^Epistola ad mathematicos de theoria arithmetices nouis a se inuentis aucta, Vindobonae

[Vienna], 1739.
"De numeris perfectis, Comm. Acad. Petrop., 7, 1740, ad annos 1734-5, 7-14.

18 History of the Theory of Numbers. [Chap, i

Johann Christoph Heilbronner^^ stated that the perfect numbers up to
4-10' are 6, 28, 496, 8128, 130816,2096128. "The fathers of the early church
and many wTiters always held this number 6 in high esteem. God com-
pleted the creation in 6 days and since all things created by Him came out
perfect, he wished the work of creation completed according to the number 6
as being a perfect number."

L. Euler" deduced from Fermat's theorem, which he here proved by
use of the binomial theorem, the result* that, if m is a prime, 2"* — 1, when
composite, has no prime factors other than those of the form wn+l.

J. Landen^^ noted that 196 is the least number 4a;'*, where x is prime, the
sum of whose ahquot parts exceeds the number by 7.

L. Euler^^ gave a table of the prime factors of 2" — 1 for n^37.

C. N. de Winsheim^° noted that 2^'^ — 1 has the factor 2351, and stated
that 2" — 1 is a prime for n = 2, 3, 5, 7, 13, 17, 19, 31, composite for the
remaining n<48, but was doubtful as to n = 41, thus reducing the Hst of
perfect numbers given by Euler^ by one or perhaps two. He suspected
that n = 41 leads to an imperfect number since it was excluded by the acute
Mersenne,^° who gave instead 2^^(2^" — 1) as the ninth perfect number. He
remarked that the basis of Mersenne's assertion is doubtless to be found in
the stupendous genius of Mersenne which perhaps recognized more truths
than he could demonstrate. He discussed the error of Hansch^ that 2" — !
is a prime if n is a prime ^ 79.

G. W. Kraft^^ considered perfect numbers AP, where P is a prime [not
dividing A]. Thus a{P-\-l)=2AP, where a is the sum of all the divisors
of A. Hence a/ {2 A— a) equals the prime P. Let 2A— a = l, a property
holding for A =2"". Then P = 2"'+^ — 1 and the resulting numbers are of
Euchd's type.

L. Euler,^- in a letter to Goldbach, October 28, 1752, stated that he
knew only seven perfect numbers, viz., 2p~^(2^ — 1) for p = 2, 3, 5, 7, 13, 17,
19, and was uncertain whether 2^^ — 1 is prime or not (a factor is necessarily
of the form 64n+l and none are <2000).

^^Historia matheseos universae. Accedit recensio elementorum compendiorum et openim math,
atque historia arithmetices ad nostra tempora, Lipsiae, 1742, 755-6. There is a 63-page
Ust of arithmetics of the 16th century.

«^^ovi Comm. Ac. Petrop., 1, 1747-8, 20; Comm. .\rith., I, 56, §39.

*We may simpUfy the proof by using the fact that 2 belongs to an e.xponent e modulo p (p a
prime) such that e divides p — 1. For, if p is a factor of 2'"— 1, m is a multiple of e, whence
e equals the prime m. Thus p — 1 =n7«. If we take m>2, we see that n is even since
p is odd and conclude with Fermat^' that, if m is an odd prime, 2"»— 1 is divisible by no
primes other than those of the form 2km + l.

"•Ladies' Diary, 1748, Question 305. The Diarian Repository, Collection of all the mathe-
matical questions from the Ladies' Diary, 1704-1760, by a society of mathematicians,
London, 1774, 509. Button's The Diarian Miscellany (from Ladies' Diarj-, 1704-1773),
London, 1775, vol. 2, 271. Leyboiu-n's Math. Quest, proposed in Ladies' D., 2, 1817,
9-10.

"Opuscula varii argumenti, Berlin, 2, 1750, 25; Comm. Arith., 1, 1849, 104.

•"Novi Comm. Ac. Petrop., 2, 1751, ad annum 1749, mem., 68-99.

"/bid., mem., 112-3.

•^Corresp. Math. Phys. (ed., Fuss), I, 1843, 590, 597-8.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 19

G. W. Kraft^^ stated (p. 114) that Euler had communicated to him pri-
vately in 1741 the fact that 2*^-1 is divisible by 2351. He stated (p. 121)
that if 2^ — 1 is composite {p being prime), it has a factor of the form
2q'^p + l, where g is a prime [including unity], using as illustrations the
factorizations noted by Euler. ^^ Of the numbers 2" — 1, n a prime ^71,
stated to be prime by Hansch,^^ six are composite, while the cases 53, . . . , 71
are in doubt (p. 115).

A. Saverien^^ repeated the remarks by Ens^^ without reference.

L. Euler^^ stated in a letter to Bernoulli that he had verified that 2^^ — 1
is a prime by examining the primes up to 46339 which are contained in the
possible forms 248n+l and 248n+63 of divisors.

L. Euler^^ gave a prime factor of 2"=»= 1 for various values of n, but no
new cases 2^—1 with n a prime.

L. Euler,^^ in a posthumous paper, proved that every even perfect number
is of Euclid's type. Let o = 2"6 be perfect, where b is odd. Let B denote
the sum of the divisors of b. The sum {2'*^^ — l)B of the divisors of a must
equal 2a. Thus 6/5 = (2"+^-l)/2"+\ a fraction in its lowest terms.
Hence 6 = (2^+^ — 1 )c. If c = l, 6 = 2"'*'^ — 1 must be a prime since the sum
of its divisors is 5 = 2""^^ whence Euclid's formula. If c>l, the sum B of
the divisors of b is not less than 6+2""''^ — 1+c+l; hence

^^2"+nc+l) 2"+'
6= h '^2"+^-l'

contrary to the earlier equation. The proof given in another posthumous
paper by Euler^^ is not complete.

L. Euler^^ proved that any odd perfect number must be of the form
y.4x+ip2^ where r is a prime of the form 4nH-l [Frenicle®^]. Express it as a
product ABC. . . of powers of distinct primes. Denote by a, b, c, . . .the
sums of the divisors oi A, B,C,. . ., respectively. Then abc . . . = 2 ABC ....
Thus one of the numbers a, b, . . . , say a, is the double of an odd number,
and the remaining ones are odd. Thus B, C,. . . are even powers of primes,
while A =r*^"^^ In particular, no odd perfect number has the form 4n+3.
Amplifications of this proof have been given by Lionnet,^^^ Stern, ^^'^ Syl-
vester, ^^^ Lucas. ^" See also Liouville^° in Chapter X.

Montucla^^ remarked that Euclid's rule does not give as many perfect
numbers as believed by various writers; the one often cited [Paciuolo^®] as
the fourteenth perfect number is imperfect; the rule by Ozanam^^ is false
since 511 and 2047 are not primes.

"Novi Comm. Ac. Petrop., 3, 1753, ad annos 1750-1.

"Dictionnaire universel de math, et physique, two vols., Paris, 1753, vol. 2, p. 216.
»^Nouv. Mim. Acad. BerUn, ann6e 1772, hist., 1774, p. 35; Euler, Comm. Arith., 1, 1849, 584.
"Opusc. anal., 1, 1773, 242; Comm. Arith., 2, p. 8.

"De numeris amicabihbus, Comm. Arith., 2, 1849, 630; Opera postuma, 1, 1862, 88.
'^Tractatus de numerorum doctrina, Comm. Arith., 2, 514; Opera postuma, 1, 14-15.
"Recreations math, et physiques par Ozanam, nouvelle 6d. par M., Paris, 1, 1778, 1790, p. 33.
Engl, transl. by C. Hutton, London, 1803, p. 35.

/

20 History of the Theory of Numbers. [Chap. I

Johann Philipp Griison^^'' made the same criticism of Ozanam"^ and
noted that, if 2"x is perfect and x is an odd prime,

1+2+ . . .+2'' = 2'*x-a:-2x-. . .-2'*-^x = x.

M. Fontana^"^ noted that the theorem that all perfect numbers are
triangular is due to Maurolycus^^ and not to T. Maier (cf. Kraft^^).

Thomas Taylor^"- stated that only eight perfect numbers have been
found so far [the 8 listed are those of Mersenne^^j.

J. Struve^^^ considered abundant numbers which are products ahc of
three distinct primes in ascending order; thus

ob+o+M-l 2 ^ .-

— ; ; >C, >C + 1.

ah-a-h-1 ' i_i_l_jL

a h ab

The case a^3 is easily excluded, also a = 2, 6^5 [except 2-5'7]. For
a = 2, 6 = 3, c any prime > 3, 6c is abundant. Next, abed is abundant if

^"^' >d+i.

a6c — (a6+ac+6c+a+6+c+l)'

For a = 2, 6 = 3, c = 5 or 7, and for a = 2, 6 = 5, c = 7, abed is abundant for
any prime d [>c]. Of the numbers ^ 1000, 52 are abundant.

J. Westerberg^*^ gave the factors of 2"='=1 for n = l,..., 32, and of
10''±l,n = l,..., 15.

O. Terquem^°^ Usted 2*^-1 and 2*^-1 as primes.

L. WantzeP"® proved the remark of Kraft*^ that if A^i be the sum of the
digits of a perfect number N>6 [of Euclid's type], and N2 the sum of the
digits of A^i, etc., a certain iV, is unity. Since iV=l(mod 9), each Ni=l
(mod 9), while the NiS decrease.

V. A. Lebesgue^°^ stated that he had a proof that there is no odd perfect
number with fewer than four distinct prime factors. For an even perfect
number 2"?/ V . . . ,

y'^" ■ ■ • +prrY = (1 +y+ ■ ■ ■ +y') d +^+ • • • +^') ■ • • »

""Enthiillte Zaubereyen und Geheimnisse der Arithmetik, erster Theil, Berlin, 1796, p. 85, and

Zusatz (end of Theil I).
»<»Memorie dell' Istituto Nazionale Ital., mat., 2, pt. 1, 1808, 285-6.
'°*The elements of a new arithmetical notation and of a new arithmetic of infinites, with an

appendix .... of perfect, amicable and other numbers no less remarkable than novel,

London, 1823, 131.
^''Ueber die so gennannten numeri abundantes oder die Ueberfluss mit sich fiihrenden Zahlen,

besonders im ersten Tausend unsrer Zahlen, Altona, 1827, 20 pp.
*'**De factoribus numerorum compositorum dignoscendis, Disquisitio Acad. CaroUna, Lundae,

1838. In the volume, Meditationum Math publice defendent C. J. D. Hill, Pt. II,

1831.
i^Nouv. Ann. Math., 3, 1844. 219 (cf. 553).
^<*Ibid., p. 337.
i"76id., 552-3.

Chap. I] PERFECT, MULTIPLY Perfect, and Amicable Numbers. 21

the impossibility of which is evident when the exponents j3, 7, . . . are other
than 1, 0, 0, . . ., a case giving Euclid's solution [cf. Desboves^^'].

C. G. Reuschle^^* gave in his table C the exponent to which 2 belongs
modulo p, for each prime p<5000. Thus 2" — 1 has the factor 1399 for
n = 233, the factor 2687 forn = 79, and 3391 for n = 113 [as stated exphcitly
by Le Lasseur^^^'^^^]. ^iso 23514513 for n = 47, 1433 for w = 179, and 1913
for n = 239. In the addition (p. 22) to Table A, he gave the prime factors of
2^* — 1 for various n's to 156, 37 being the least n for which the decomposition
is not given completely, while 41 is the least n for which no factor is known.
For 34 errata in Table C, see Cunningham^^° of Ch. VII.

F. Landry^^^ gave a new proof that 2^^ — 1 is a prime.

Jean Plana^^° gave (p. 130) the factorization into two primes:

2*^-1 = 13367X 164511353.

His statement (p. 141) that 2^^ — 1 has no factor < 50033 was corrected by
Landry^^^ (quoted by Lucas, "^ p. 280) and Gerardin."'

Giov. Nocco^" showed that an odd perfect number has at least three
distinct prime factors. For, if a"*6'* is perfect,

2a- = V-T^' 6" = ^ -^,

0—1 a— 1

whence

^ ^ Q^""^^ _(a-l)b"+l
2(5-1)" 2(6 -l)a"»" 6"+^-l '

a+fe(a6"+26"-'+2)=2+6(26"+2a6"-^).

But the minunum values of a, h are 3, 5. Thus 6(a— 2)>2a — 2,

a6''-26" = 6"-^-6(a-2)>6'*-^(2a-2), a6'»+26"-'>26"+2a6''-\

contrary to the earlier equation. In attempting to prove that every even
perfect number 2'"6Vd' ... is of EucUd's type, he stated without proof that

2-+16V. . . =(2"'+^-l)J5C. . ., B= \ /, C = - -,.. .

0 — 1 c — 1

require that 2"*+^ = B, 6" = 2^"+^ - 1 , d' = C, . . . (the first two of which results
yield Euclid's formula).

F. Landry^^^ stated (p. 8) that he possessed the complete decomposi-
tion of 2"±l(n^64) except for 2^^±1, 2«Hl, and gave (pp. 10-11) the
factors of 2^^-l and of 2"+l for n = 65, 66, 69, 75, 90, 105.

"^Mathematische Abhandlung, enthaltend neue Zahlentheoretische Tabellen sammt einer
dieselben betreflfenden Correspondenz mit dem verewigten C. G. J. Jacobi. Prog., Stutt-
gart, 1856, 61 pp. Described by Kummer, Jour, fur Math., 53, 1857, 379.

^°'Proc6des nouveaux pour demontrer que le nonabre 2147483647 est premier. Paris, 1859.
Reprinted in SpLinx-Oedipe, Nancy, 1909, 6-9.

""Mem. Reale Ac. Sc. Torino, (2), 20, 1863, dated Nov. 20, 1859.

'"Alcune teorie su'numeri pari, impari, e perfetti, Lecce, 1863.

"^Aux math^maticiens de toutes les parties du monde: communicatidn but la decomposition des
nombres en leurs facteurs simples, Paris, 1867, 12 pp.

22 History of the Theory of Numbers. [Chap. I

F. Landry"^ soon published his table. It includes the entries (quoted

byLucas^2o.i22).

2«-l=431-9719-2099863, 2*^-1=23514513.13264529,
253-1 = 6361.69431-20394401, 2^^-1 = 179951.3203431780337,

the least factors of the first two of which had been given by Euler.^' •'
This table was republished by Lucas^-^ (p. 239), who stated that only three
entries remain in doubt: 2^^ — 1, (2^^ + l)/3, 2^*+l, each being conjectured
a prime by Landry. The second was believed to be prime by Kraitchik.^^^"
Landr>''s factors of 2"+l, for 28^n^64 were quoted elsewhere."^''

Jules Carvallo^^* announced that he had a proof that there exists no odd
perfect number. Without indication of proof, he stated that an odd per-
fect number must be a square and that the ratio of the sum of the divisors
of an odd square to itself cannot be 2. The first statement was abandoned
in his published erroneous proof, ^^^ while the second follows at once from
the fact that, when p is an odd prime, the sum of the 2n+l divisors, each
odd, of p^" is odd.

E. Lucas^^^ stated that long calculations of his indicated that 2°^ — 1
and 2^^ - 1 are composite [cf . Cole,^" Powers^^^]. See Lucas-° of Ch. XVII.

E. Lucas^^^ stated that 2^^ — 1 and 2^^^ — 1 are primes.

E. Catalan^^^ remarked that, if we admit the last statement, and note
that 2^ — 1, 2^ — 1, 2^ — 1 are primes, we may state empirically that, up to a
certain limit, if 2" — 1 is a prime p, then 2^ — 1 is a prime g, 2^ — 1 is a prime,
etc. [cf. Catalan^^^].

G. de Longchamps^^'^ suggested that the composition of 2"±1 might be
obtained by continued multiplications, made by simple displacements from
right to left, of the primes written to the base 2.

E. Lucas^^^ verified once only that 2^^^ — 1, a number of 39 digits, is a
prime. The method will be given in Ch. XVII, where are given various
results relating indirectly to perfect numbers. He stated (p. 162) that he
had the plan of a mechanism which will permit one to decide almost instan-
taneously whether the assertions of Mersenne and Plana that 2" — 1 is a
prime for n = 53, 67, 127, 257 are correct. The inclusion of n = 53 is an
error of citation. He tabulated prime factors of 2" — 1 for n^40.

E. Lucas^^^ gave a table of primes with 12 to 16 digits occurring as a
factor in 2"-l for n = 49, 59, 65, 69, 87, and in 2''+l forn = 43, 47, 49, 53,
69, 72, 75, 86, 94, 98, 99, 135, and several even values of n>100. The

'"Decomposition des nombres 2"=!= 1 en leurs facteurs premiers de n = 1 ^ n = 64, moins quatre,

Paris, 1869, 8 pp.
"3<»Sphinx-0edipe, 1911, 70, 95.
"'^L'interm^diaire des math., 9, 1902, 186.
'"Comptes Rendus Paris, 81, 1875, 73-75.

"'Sur la th^orie des nombres premiers, Turin, 1876, p. 11; TWorie des nombres, 1891, 376.
"«Nouv. Corresp. Math., 2, 1876, 96.
i^Comptes Rendus Paris, 85, 1877, 950-2.

"sBull. Bibl. Storia Sc. Mat. e Fis.; 10, 1877, 152 (278-287). Lucas"- " of Ch. XVII.
"'Atti R. Ac. Sc. Torino, 13, 1877-8, 279.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 23

verification of the primality was made by H. Le Lasseur. To the latter
is attributed (p. 283) the factorization of 2'*-! for n = 73, 79, 113. These
had been given without reference by Lucas. ^^°

E. Lucas^^^ proposed as a problem the proof that if 8q+7 is a prime,
24a+3_i is not.

E. Lucas^^^ stated as new the assertion of Euler^^ that if 4m — 1 and
8m — 1 are primes, the latter divides A = 2*"*~^ — 1.

E. Lucas^^^ proved the related fact that if 8m — 1 is a prime, it divides A.
For, by Fermat's theorem, it divides 2^"*"^ — 1 and hence divides A or
2^~^H-1. That the prime 8m — 1 divides A and not the latter, follows from
Euler's criterion that 2^^"^^''^ — 1 is divisible by the prime p if 2 is a quad-
ratic residue of p, which is the case if p = 8m='=l. No reference was made
to Euler, who gave the first seven primes 4m — 1 for which 8m — 1 is a prime.
Lucas gave the new cases 251, 359, 419, 431, 443, 491. Lucas^^^ elsewhere
stated that the theorem results from the law of reciprocity for quadratic
residues, again without citing Euler. Later, Lucas^^^ again expressly
claimed the theorem as his own discovery.

T. Pepin^^^ noted that if p is a prime and q = 2^ — 1 is a quadratic non-
residue of a prime 4n + 1 = a^ + 6^, then qisa, prime if and only if (a — hi) / (o + hi)
is a quadratic non-residue of q.

A. Desboves^^^ amplified the proof by Lebesgue^^^ that every even per-
fect number is of Euclid's type by noting that the fractional expression in
Lebesgue's equation must be an integer which divides y^z'^ . . . and hence is
a term of the expansion of the second member. Hence this expansion
produces only the two terms in the left member, so that (j8+l)(7+l) . . . = 2.
Thus one of the exponents, say /3, is unity and the others are zero. The
same proof has been given by Lucas^^^ (pp. 234-5) and Th^orie des Nombres,
1891, p. 375. Desboves (p. 490, exs. 31-33) stated that no odd perfect
number is divisible by only 2 or 3 distinct primes, and that in an odd perfect
number which is divisible by just n distinct primes the least prime is less
than 2".

F. J. E. Lionnet^^* amplified Euler's^^ proof about odd perfect numbers.
F. Landry^^^ stated that 2^^=*= 1 are the only cases in doubt in his table."'
Moret-Blanc^^° gave another proof that 2^^ — 1 is a prime.

""Assoc. franQ. avanc. sc, 6, 1877, 165.

»2iNouv. Corresp. Math., 3, 1877, 433.

i"Mess. Math., 7, 1877-8, 186. AJso, Lucas.""

i«Amer. Jour. Math., 1, 1878, 236.

i^^BuU. Bibl. Storia Sc. Mat. e Fis., 11, 1878, 792. The results of this paper will be cited in Ch.

XVI.
^Recreations math., ed. 2, 1891, 1, p. 236.
"^Comptes Rendus Paris, 86, 1878, 307-310.
"'Questions d'algebre 616mentau-e, ed. 2, Paris, 1878, 487-8.
'"Nouv. Ann. Math., (2), 18, 1879, 306.

"sBull. Bibl. Storia Sc. Mat., 13, 1880, 470, letter to C. Henry.
"«Nouv. Ann. Math., (2), 20, 1881, 263. Quoted, with Lucas' proof, Sphinx-Oedipe, 4,

1909, 9-12.

24 History of the Theory of Numbers. [Chap, i

H. LeLasseur found after^^^ 1878 and apparently just before^^^ 1882
that 2'*-l has the prime factor 11447 if n = 97, 15193 if n = 211, 18121 if
71 = 151, 18287 if n = 223, and that there is no divisor <30000 of 2"-l for
the 24 prime values of n, n^257, which remain in doubt, viz. [cf. Lucas^^^],

61, 67, 71, 89, 101, 103, 107, 109, 127, 137, 139, 149,
157, 163, 167, 173, 181, 193, 197, 199, 227, 229, 241, 257.

J. Carvallo^^^ attempted again^^* to prove the non-existence of odd
perfect numbers y^'z^ . . .u\ where y,. . .u are distinct odd primes. He began
by noting that one and only one of the exponents n, . . ., r is odd [Euler^^].
Let y<z< . . .<u, and call their number jjl. From the definition of a
perfect number,

y — l "' u — 1 ' y — l'u — l

The fractions in this inequality form a decreasing series. Hence

fe)'>^. ^<A' -~i>^' H^r

Thus w(2 — A;)<2. By a petitio principii (the division by 2— A:, not known
to be positive), it was concluded (p, 10) that

^<2i:^' ^^<2, y>2i/(M-i)_i-

[This error, repeated on p. 15, was noted by P. Mansion. ^^] For a
given n, there is at most one prime between the two limits (of difference < 2)
for y. A superior limit is found for 2 as a function of y. An incomplete
computation is made to show that, if /x>8, z <y-\-l.

It is shown (p. 7) that an odd perfect number has a prime factor greater
than the prime factor w entering to an odd power, since w+l divides the
sum of the divisors. In a table (p. 30) of the first ten perfect numbers,
2^^ — 1 and 2*^ — 1 are entered as primes [contrary to Euler^^ and Plana^^°].

E. Catalan^^^ stated that 2^ — 1 is a prime if p is a prime of the form
2^ — 1. If correct this would imply that 2^^^ — 1 is a prime [cf. Catalan^^^].

E. Lucas^^^ repeated the remark of LeLasseur^^^ on the 24 prime values
of n^257 for which the composition of 2^ — 1 is in doubt. According to a

"iSince these four values of n are included in the list by Lucas^** of the 28 values of n ^ 257 for
which the composition of 2"—! is unknown. Cf. Lucas^^^ p. 236.

"2Lucas, Recreations math., 1, 1882, 241; 2, 1883, 230. Later, Lucas^^s credited LeLasseur
with these four cases as well as n = 73 [Eulers^] and n = 79, 113, 233 [cf. Reuschlei"].
The last four cases were given by Lucas"*, while the last three do not occur in the table
(Lucasi24^ pp 7gg_9) by LeLasseur of the proper divisors of 2"— 1 for each odd n, n<79,
and for a few larger composite n's. The last three were given also by Lucas"^ (p. 236)
without reference.

'"Th^orie des nombres parfaits, par M. Jules Carvallo, Paris, 1883, 32 pp.

"<Mathesis, 6, 1886, 147.

'"Melanges Math., Bruxelles, 1, 1885, 376.

'"Mathesis, 6, 1886, 146.

Chap. IJ PERFECT, MULTIPLY PERFECT, AND AMICABLE NUMBERS. 25

communication from Pellet, 2" — 1 is divisible by 6n+l if n and 6n+l are
primes such that 6n+l =4L^+27M^ [provided* n= 1 (mod 4), i. e., L is odd].

M. A. Stern^" amplified Euler's^^ proof concerning odd perfect numbers.

E. Lucas^^^ repeated the statement [Desboves^^^] that an odd perfect
number must contain at least four distinct primes.

G. Valentin^^^ gave a table, computed in 1872, showing factors of
2"— 1 for n = 79, 113, 233, etc., but not the new cases of LeLasseur.^^^

The primality of iV = 2®^ — 1, a number of 19 digits, considered composite
by Mersenne and prime by Landry, was established by J. Pervusin"° and
P. Seelhoff ^^^ independently. The latter claimed to verify that there is no
factor <N^'^ of the form 8?i+7, abbreviating the work by use of various
numbers of which iV is a quadratic residue; thus iV is a prime or the product
of two primes. Since iV = 2(2^°)^ — 1, 2 is a quadratic residue of any prime
factor of N, so that the factor is 8n=i= 1. It was verified that 3^= 1 (mod N),
where i8 = (iV — 1)/9. If N=fF, where F is the prime factor 8n-|-l, then
3^^1(mod F) and, by Fermat's theorem, 3^~^=l(mod F). It is stated
without proof that one of the exponents /S and F — 1 divides the other.
Cole^^^ regarded the proof as unsatisfactory.

Seelhoff proved that a perfect number of the form pV is of Euclid's
type if p and r are primes and p<r. The condition is

r''+\2-p)-2r''{l-p)-p
If p > 2, the denominator is negative. Hence p = 2 and

^'=2K^' 2'+' = r+;j-j, p = l, r=2-+'-l.

His statements (p. 177) about the factors of 2" — 1, n = 37, 47, 53, 59,
were corrected by him {ibid., p. 320) to accord with Landry.^^^

P. Seelhoff ^^^ obtained the known factors of these 2" — 1 and proved that
2^^ — 1 is a prime, by use of his method of quadratic residues.

H. Novarese^^^ proved that every perfect number of Euclid's type ends
in 6 or 28, and that each one > 6 is of the form 9A;+1.

Jules Hudelot"^ verified in 54 hours that 2^^ — 1 is a prime by use of the
test by Lucas, Recreations math., 2, 1883, 233.

♦Correction by Kraitchik, Sphinx-Oedipe, 6, 1911, 73; Pellet, 7, 1912, 15.
"'Mathesis, 6, 1886, p. 248.
"8/6td., p. 250.

""Archiv Math. Phys., (2), 4, 1886, 100-3.
""Bull. Acad. Sc. St. Petersb., (3), 31, 1887, p. 532; Melanges math. astr. ac. St. P^tersb., 6,

1881-8, 553; communicated Nov. 1883.
"iZeitschr. Math. Phys., 31, 1886, 174-8.

»"Archiv Math. Phys., (2), 2, 1885, 327; 5, 1887, 221-3 (misprint forn = 41).
*«Jomal de sciencias math, e astr., 8, 1887, 11-14. [Servais"*.]
"♦Mathesis, 7, 1887, 46. Sphinx-Oedipe, 1909, 16.

26 History of the Theory of Numbers. [Chap, i

CI. Servais"^ republished the proofs by Novarese^"*^ and proved that
a'"6'* is not perfect if a and h are odd primes. For, by the equations [Nocco"^]

a-+i_l = 6"(a-l), b''+^-l=2a"'(6-l),

we obtain, by subtraction,

Thus2a'">6". Since a^3, a'"+^^3a"'>a'"+6'*>a+6-l. He next proved
that, if an odd perfect number is divisible by only three distinct primes a,
h, c, two of them are 3 and 5, since [as by Carvallo^^^]

04)04)04)<l

Taking a = 3, 6 = 5, we have c<16, whence c = 7, 11, or 13. He quoted
from a letter from Catalan that the sum of the reciprocals of the divisors
of a perfect number equals 2.

E. Cesaro^*^ proved that in an odd perfect jiumber containing n distinct
prime factors, the least prime factor is ^n\/2.

CI. Servais^^^ showed that it does not exceed n since, if a<h<c< . . . ,

b a+1 c a-\-2

6 — 1 a c — \ a+1

ah a a+1 a+2 a-\-n — \

2i^. . . ^ . . . . >

a—lb—1 ' a— r a a+1 a+n— 2

whence 2(a — l)<a+n — 1, a<n+l. If I is the (m — l)th prime factor and
s is the 772th, and if

a b

a-l'b-l"l-l
then

^L<2,

s+1 s+n—m _. ^L{n—m)-\-2

>2, s<

s — l s ' ' ' s-\-n—m-\-l ' 2—L

J. J. Sylvester ^'^^ reproduced Euler's^^ proof that every even perfect
number is of EucUd's type. From the fact that ■|.|-<2, he concluded that
there is no odd perfect number a'"6'*. For the case of three prime factors
he obtained the result of Servais^'*^ in the same manner. He proved that
no odd perfect number is divisible by 105 and stated that there is none with
fewer than six distinct prime factors.

Sylvester^^^ and Servais^^*^ gave complete proofs that there exists no odd
perfect number with only three distinct prime factors.

i«Mathesis, 7, 1887, 228-230.
»«/6id., 245-6.
"'Mathesis, 8, 1888, 92-3.
"8Nature, 37, Dec. 15, 1887, 152 (minor correction, p. 179); Coll. Math. Papers, 4, 1912, 588.
"'Comptes Rendus Paris, 106, 1888, 403-5 (correction, p. 641); reproduced with notes by P.
Mansion, Mathesis, 8, 1888, 57-61. Sylvester's Coll. Math. Papers, 4, 1912, 604, 615.
""Mathesis, 8, 1888, 135.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AMICABLE NUMBERS. 27

Sylvester ^^^ proved there is no odd perfect number not divisible by 3
with fewer than eight distinct prime factors.

Sylvester^^^ proved there is no odd perfect number with four distinct
prime factors.

Sylvester^^^ spoke of the question of the non-existence of odd perfect
numbers as a "problem of the ages comparable in difficulty to that which
previously to the labors of Hermite and Lindemann environed the subject
of the quadrature of the circle." He gave a theorem useful for the investi-
gation of this question: For r an integer other than 1 or —1, the sum
l+r+r^+ . . . -\-r^~^ contains at least as many distinct prime factors as p
contains divisors >1, with a possible reduction by one in the number of
prime factors when r= — 2, p even, and when r = 2, p divisible by 6.

E. Catalan ^^^ proved that if an odd perfect number is not divisible by
3, 5, or 7, it has at least 26 distinct prime factors and thus has at least 45
digits. In fact, the usual inequality gives

lTl3-- I ^2 ^^^^"3 5 7 11 • I <2 3 5 7<^-^^^^-

By Legendre's table IX, Theorie des nombres, ed. 2, 1808; ed. 3, 1830, of
the values of P{w) up to w; = 1229, we see that I ^ 127. But 127 is the 27th
prime >7.

R. W. D. Christie^^^ erroneously considered 2^^ — 1 and 2^^ — 1 as primes.

E. Lucas^^® proved that every even perfect number, aside from 6 and
496, ends with 16, 28, 36, 56, or 76; any one except 28 is of the form 7k='= 1 ;
any one except 6 has the remainder 1,2, 3, or 8 when divided by 13, etc.

E. Lucas^" reproduced his^^^ proofs and the proof by Euler,^^ and gave
(p. 375) a list of known factorizations of 2" — 1.

Genaille^^^ stated that his machine "piano arithm^tique " gives a prac-
tical means of applying in a few hours the test by Lucas {ibid., 5, 1876, 61)
for the primality of 2" — 1 .

J. Fitz-Patrick and G. ChevreP^^ stated that 2^8(229-1) is perfect.

E. Fauquembergue^®^ found that 2®'' — 1 is composite by a process not
yielding its factors [cf. Mersenne,^" Lucas,^^^ Cole^'^^].

A. Cunningham^^^ called 2^ — 1 a Lucassian if p is a prime of the form
4A;+3 such that also 2p+l is a prime, stating that Lucas^^^ had proved that
2'' — 1 has the factor 2p+l. Cunningham listed all such primes p<2500

i"Comptes Rendus Paris, 106, 1888, 448-450; Coll. M. Papers, IV, 609-610.

^mid., 522-6; Coll. M. Papers, IV, 611-4.

""Nature, 37, 1888, 417-8; Coll. M. Papers, IV, 625-9.

""Mathesis, 8, 1888, 112-3. M6m. soc. sc. Ukge, (2), 15, 1888, 205-7 (Melanges math., III).

»*Math. Quest. Educat. Times, 48, 1888, p. xxxvi, 183; 49, p. 85.

"«Mathe8is, 10, 1890, 74-76.

"'Theorie des nombres, 1891, 424-5.

"'Assoc, frang. avanc. sc, 20, I, 1891, 159.

"'Exercices d'Arith., Paris, 1893, 363.

""L'interm^diaire des math., 1, 1894, 148; 1915, 105, for representations by u*+67t;*.

""British Assoc. Reports, 1894, 563.

28 History of the Theory of Numbers. [Chap, i

and considered it probable that primes of the forms 2''±1, 2'^S (if not
yielding Lucassians) generally yield prime values of 2^ — 1, and that no
other primes will. All known and conjectured primes 2^ — 1, with p prime,
fall under this rule.

In a letter to Tannery/^- Lucas stated that Mersenne^°'^^ implied that
a necessary and sufficient condition that 2^—1 be a prime is that p be a
prime of one of the forms 2^"+l, 2^''±3, 2^"+^ — 1. Tannery expressed his
behef that the theorem was empirical and due to Frenicle, rather than to
Fermat, and noted that the sufficient condition would be false if 2^' — 1 is
composite [as is the case, Fauquembergue^^°].

Goulard and Tannery^^^ made minor remarks on the subject of the last
two papers.

A. Cunningham^^ found that 2^^' - 1 has the factor 7487. This contra-
dicts LeLasseur's^^- statement on di visors < 30000 of Mersenne's numbers.

A. Cunningham^^^ found 13 new cases (317, 337, 547, 937, . . .) in which
2^—1 is composite, and stated that for the 22 outstanding primes 5^257
[above list^^- except 61, 197] 2^ — 1 has no divisor < 50,000 (error as to
q = lSl, see Woodall^^). The factors obtained in the mentioned 13 cases
were found after much labor by the indirect method of Bickmore,^^^ who
gave the factors 1913 and 5737 of 2-^^-1.

A. Cunningham^" gave a factor of 2^-1 for g = 397, 1801, 1367, 5011
and for five larger primes q.

C. Bourlet"^ proved that the sum of the reciprocals of all the divisors
di of a perfect number n equals 2 [Catalan ^^^], by noting that n/di ranges
with di over the divisors of n, so that 2n = 'Zn/di. The same proof occurs
in II Pitagora, Palermo, 16, 1909-10, 6-7.

M. Stuyvaert^^^ remarked that an odd perfect number, if it exists, is a
sum of two squares since it is of the form pk^, where p is a prime 4n+l
[Frenicle,^ Euler^sj

T. Pepin^"° proved that an odd perfect number relatively prime to 3-7,
3-5 or 3-5-7 contains at least 11, 14 or 19 distinct prime factors, respectively,
and can not have the form 6/cH-5.

F. J. Studnicka^^^ called Ep = 2''-\2''-l) an Euclidean number if 2^-1
is a prime. The product of all the divisors <Ep of Ep is E/~'^. When
Ep is written in the diadic system (base 2), it has 2p — l digits, the first p of
which are unity and the last p — 1 are zero.

"^L'interm^diaire des math., 2, 1895, 317.

i«/6Mi., 3, 1896, 115, 188, 281.

^"Nature, 51, 1894-5, 533; Proc. Lond. Math. Soc, 26, 1895, 261; Math. Quest. Educat. Times,

5, 1904, 108, last footnote.
i«British Assoc. Reports, 1895, 614.
i«On the numerical factors of a"-l, Messenger Math., 25, 1895-6, 1-44; 26, 1896-7, 1-38.

French transl. by Fitz-Patrick, Sphinx-Oedipe, 1912, 129-144. 155-160.
"Troc. London Math. Soc, 27, 1895-6, 111.
"8Nouv. Ann. Math., (3), 15, 1896, 299.
"•Mathesis, (2), 6, 1896, 132.

''"Memou-e Accad. Pont. Nuovi Lincei, 13, 1897, 345-420.
"'Sitzungsber. Bohm. Gesell., Prag, 1899, math, nat., No. 30.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 29

Mario Lazzarini^" attempted to prove that there is no odd perfect num-
ber a'^b^c'^, but made the error of thinking that a is relatively prime to
6^+. . .+6+1. He attempted to show that p = 2" — 1 is a prime if and
only if p divides iV = 3*^+1, where fc = 2"~^ — 1 [false for a = 2, since p = S,
N = 4:]. He restricted his argument to the case a odd, whence p = 1 (mod 3) .
Then, if p is a prime, —3 is a quadratic residue of p, so that (— 3)^^~^^^^=1
(mod p), whence p divides N. Conversely, when this congruence holds, he
concluded falsely that z^=—3 (mod p) has two and only two roots, so that
p is expressible in a single way as a sum of a square and the triple of a square
and hence is prime. To show the error, let p = ab, where a = 23, 6 = 3851 are
primes; then

g-l 6-1

(-3)11 + 1= _2a6,(-3) 2 =-l(mod5),(-3) ^ =(-3)^^-^^^= -1 (mod a),

whence (—3)^^"^^^^=! (mod p). Cipolla remarked (p. 288) that we may
deduce from a result of Lucas^^° that p is a prime if it divides N without
dividing 3*+l for any divisor 8 of p=2"~^ — 1.

F. N. Cole^'^ found that 2^"^ - 1 is the product of the two primes 193707721 ,
761838257287. In the footnote to p. 136, he criticized the proof by Seel-
hoff"^ of the primality of A^ = 2^^ — 1 and stated he had verified that N is
prime by an actual computation of a series of primes of which iV is a
quadratic residue.

R. D. Carmichael^^^ proved that any even perfect number Tp2\ . .p/"
is of Euclid's type. Write d for 2'*+^ — 1. Then, as usual,

d pf d \ p/

If n>2. Pi is less than d, being an aliquot divisor of it, so that 1 + 1/p,
exceeds the left member of the inequality. Hence n = 2, p2 = d.

A. Cunningham^^^ gave the residues of A; =2^"*, 2*, etc., modulo 2^ — 1 for
primes g^lOl.

A. Turcaninov^"^ (Turtschaninov) proved that an odd perfect number
has at least four distinct prime factors and exceeds 2000000.

A. Gerardin^^^ noted the error by Plana. ^^°

A. Gerardin^^^ stated the empirical laws: If n is a prime of the form
24a^+ll and if 2" — 1 is composite, the least factor is of the form 24?/ +23

"^Periodico di mat. insegn. sec, 18, 1903, 203; criticized by C. Ciamberlini, p. 283, and by M.

Cipolla, p. 285.
i"Bull. Amer. Math. Soc, 10, 1903-4, 134-7. French transl., Sphinx-Oedipe, 1910, 122-4.

Cf. Fauquembergue.^^"
i^^Annals of Math., (2), 8, 1906-7, 149.
I'sproc. London Math. Soc, (2), 5, 1907, 259 [250].
i'6 Vest, opytn. fiziki (Spaczinskis Bote), Odessa, 1908, No. 461 (pp. 106-113), No. 463 (162-3),

No. 465-6 (213-9), No. 470 (314-8). In Russian. Cf. Bourlet.is*
'"L'interm^diaire des math., 15, 1908, 230-1.
'"Sphinx-Oedipe, Nancy, 3, 1908-9, 113-123; Assoc, frang. avanc sc, 1909, 145-156. In Wis-

kundig Tijdschrift, 10, 1913, 61, he added that in the remaining three cases <257, n = 107,

167, 227, the least divisor (necessarily >1 mUlion) is respectively 5136 y+2783,

8016 y+335, 10896 J/+5903.

30 History of the Theory of Numbers. [Chap, i

{e. g., n = ll, 59, 83, 131, 179, 251). If n is a prime 24a:+23 and 2'*-l is
composite, the least factor is of the form 48?/ +47 (e. g., n = 47, ?/ = 48, factor
2351; n = 23, 71, 191, 239). Gerardin^^^ gave tables of the possible, but
(unverified, factors of 2" — 1, n<257.

A. Cunningham^^o gave the factor 150287 of 2^^^-\.

A. Cunningham^^^ found the factor 228479 of 2^^-l.

T. M. Putnam^^^ proved that not all of the r distinct prime factors of a
perfect number exceed 1 +r/loge2 and hence do not all equal or exceed 1 +3r/2.

L. E. Dickson^^^ gave an immediate proof that every even perfect num-
ber is of Euclid's type. Let 2"g be perfect, where q is odd and n > 0. Then
(2"+^ — l)s = 2'^'^^q, where s is the sum of all the divisors of q. Thus s = q-\-d,
where d = q/{2''^^ — l). Hence d is an integral divisor of q, so that q and d
are the only divisors of q. Hence d = \ and 5 is a prime.

H. J. WoodalP^^ obtained the factor 43441 of 2^^^-l.

R. E. Powers^^^ verified that 2^^ — 1 is a prime by use of Lucas' test on
the series 4, 14, 194, .... H. Tarry^^^ made an incomplete examination.
E. Fauquembergue^^^ proved that 2^^ — 1 is a prime by writing the residues
of that series to base 2.

A. Cunningham^^^ noted that 2^ — 1 is composite for three primes of 8 digits.
On the proof-sheets of this history, he noted that the first two should be

g = 67108493, p = 134216987; 5 = 67108913, p = 134217827.

A G^rardin^^^'' observed that 2'^''+^-\=F^-2(?, F = 2"+^±l = 2m+l,
G = 2"±l, G2 = m2+(m+l)2-(2")2.

H. Tarry^^^^ verified for the known composite numbers 2^—1, where p
is a prime, that, if a is the least factor, 2" — 1 is composite.

A. Gerardin added empirically that, if p is any number and a any di-
visor of 2^ — 1 , a = 8m =t 1 not being of the form 2" — 1 then 2" — 1 is composite.

A. Cunningham^^^ noted that, if g is a prime,

M^ = 2^-\ = T^-2{quY={qtf-2U\

If Mq is a prime it can be expressed in the forms A^-]-?>B^ — G'^-\-QH'^, and
in one or the other of the pairs of forms f^au^ {ci = '^, 14, 21, 42). He
discussed M^ to the base 2.

>'»Sphinx-Oedipe, 3, 1908-9, 118-120, 161-5, 177-182; 4, 1909, 1-5, 158, 168; 1910, 149, 166.
""Proc. London Math. Soc, (2), 6, 1908, p. xxii.

"iL'intermddiaire des math., 16, 1909, 252; Sphinx-Oedipe, 4, 1909, 4e Trimestre. 36-7.
"2Amer. Math. Monthly, 17, 1910, 167. ^^Ibid., 18, 1911, 109.

'"Bull. Amer. Math. Soc, 16, 1910-11, 540 (July, 1911). Proc. London Math. Soc, (2), 9,

1911, p. xvi. Mem. and Proc. Manchester Literary and Phil. Soc, 56, 1911-12, No. 1, 5 pp.

Sphinx-Oedipe, 1911, 92. Verification by J. Hammond, Math. Quest. Solutions, 2,

1916, 30-2.
i«Bull. Amer. Math. Soc, 18, 1911-12, 162 (report of meeting Oct., 1911). Amer. Math.

Monthly, 18, 1911, 195. Sphinx-Oedipe, Feb., 1912, 17-20.
"«Sphinx-Oedipe, Dec, 1911, p. 192; 1912, 15. (Proc. London Math. Soc, (2), 10, 1912,

Records of Meetings, 1911-12, p. ii.)
^"Ibid., 1912, 20-22. "^Messenger Math., 41, 1911, 4.

"saBuU. Soc. Philomatiquesde Paris, (10), 3, 1911, 221. isseSphinx-Oedipe, 6, 1911, 174 186, 192.
""Math. Quest. Educ Times, (2), 19, 1911, 81-2; 20, 1911, 90-1, 105-6; 21, 1912, 58-9, 73.

Chap.i] Perfect, Multiply Perfect, and Amicable Numbers. 31

A. Cunningham^^o found the factor 730753 of 2^^^-l.

V. Ramesam^^i verified that the quotient of 2"^-l by the factor 228479
[Cunningham^^^] is the product of the primes 48544121 and 212885833.

A. Aubry^^^ stated erroneously that ''Mersenne affirmed that 2" — 1 is
a prime, for n^257, only for n = l, 2, 3, 4, 8, 10, 12, 29, 61, 67, 127, 257
(which has now been almost proved) ; this proposition seems to be due to
Frenicle.^'" What Mersenne^" actually stated was that the first 8 perfect
numbers occur at the lines marked 1, 2, 3, 4, 8, etc., in the table by Bungus.

A. Cunningham^^^'' noted that M113, M151, M251 have the further factors
23279-65993, 55871, 54217, respectively. Cf. Reuschle^o^ Lucas^^s

A. Gerardin^^-^ noted that there is no divisor < 1000000 of the composite
Mersenne numbers not already factored. Let d denote the least divisor
of 2«- 1, g a prime ^257. li q = 60z^+43, then d=47 (mod 96), except for
the cases given by Euler's^^ theorem (verified for 43, 163, 223). If
5 = 40w+33, d=7 (mod 24), verified for 73, 113, 233. If 5 = 30m+l, d=l
(mod 24), verified for 31, 61, 151, 181, 211.

E. Fauquembergue^^^'' proved that 2^°^ — 1 is composite by means of
Lucas' test with 4, 14, 194,. . ., written to base 2 (Ch. XVII).

L. E. Dickson^^^ called a non-deficient number primitive if it is not a
multiple of a smaller non-deficient number, and proved that there is only
a finite number of primitive non-deficient numbers having a given number
of distinct odd prime factors and a given number of factors 2. As a
corollary, there is not an infinitude of odd perfect numbers with any given
number of distinct prime factors. There is no odd abundant number with
fewer than three distinct prime factors; the primitive ones with three are

3^5-7, 32527, 325.72, 3^5211, 3^13, 3*5^13, 3*52132, 3^5^132.

There is given a list of the numerous primitive odd abundant numbers with
four distinct prime factors and lists of even non-deficient numbers of certain
types. In particular, all primitive non-deficient numbers < 15000 are
determined (23 odd and 78 even). In view of these lists, there is no odd
perfect number with four or fewer distinct prime factors (cf . Sylvester^*^"^^^) .
A. Cunningham^^* gave a summary of the known results on the composi-
tion of the 56 Mersenne numbers Mq = 2^ — 1, q a prime ^257. Of these,
12 have been proved prime: M^, 5 = 1, 2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 127;
while 29 of them have been proved composite. Thus only 15 remain in

""British Assoc. Reports, 1912, 406-7. Sphinx-Oedipe, 7, 1912, 38 (1910, 170, that 730753

is a possible factor). Cf. Cunningham"*.
i"Nature, 89, 1912, p. 87; Sphinx-Oedipe, 1912, 38. Jour, of Indian Math. Soc, Madras, 4

1912, 56.
"K)euvres de Fermat, 4, 1912, 250, note to p. 67.
"2" Mem. and Proc. Manchester Lit. and Phil. Soc, 56, 1911-2, No. 1.
i«* Sphinx-Oedipe, 7, 1912, num^ro special, 15-16.
"'•^ Ibid., Nov., 1913, 176.
i«Amer. Jour. Math., 35, 1913, 413-26.
"*Proc. Fifth International Congress, I, Cambridge, 1913, 384-6. Proc. London Math. Soc,

(2), 11, 1913, Record of Meeting, Apr. 11, 1912, xxiv. British Assoc. Reports, 1911,

321. Math. Quest. Educat. Times, (2), 23, 1913, 76.

32 History of the Theory of Numbers. [Chap. I

doubt: M„ q = 101, 103, 107, 109, 137, 139, 149, 157, 167, 193, 199, 227,
229, 241, 257. The last has no factor under one million, as verified by
R. E. Powers. ^^^^ No one of the other 14 has a factor under one milhon, as
verified t^dce with the collaboration of A. G^rardin. Up to the present
three errors have been found in Mersenne's assertion; Mqj has been proved
composite (Lucas,^^° Cole^^^), while Mqi and Mgg have been proved prime
(Pervusin,"° Seelhoff,^*^ Cole,^"^ Powers^^^). It is here announced that M^^
has the factor 730753, found with the collaboration of A. Gerardin.

J. ]McDonnell^^^ commented on a test by Lucas in 1878 for the primality
of 2"-l.

L. E. Dickson^^® gave a table of the even abundant numbers <6232.

R. Niewiadomski^^^ noted that 2^^^ — 1 has the factor 4567 and gave
known factors of 2'* — 1. He gave the formula

2^'"+^-l = (2^'"+2"*-l)^+(22"'-2'"-l)^ + l.

G. Ricalde^^^ gave relations between the primes p, q and least solutions of
22«+i_i = pg, al-2h^ = p, c'-2dr = q.

R. E. Powers^^^ proved that 2^°" — 1 is a prime by means of Lucas'^^ test
in Ch. XVII.

E. Fauquembergue^'''' proved that 2^ — 1 is prime for p = 107 and 127,
composite for p = 101, 103, 109.

T. E. Mason-°^ described a mechanical de\'ice for applying Lucas'"^
method for testing the primality of 2^^'*'^ — 1.

R. E. Powers^°^ proved that 2^°^ — 1 and 2^°^ — 1 are composite by means
of Lucas' tests with 3, 7, 47, . . .and 4, 14, 194. . . (Ch. XVII), respectively.

A. Gerardin^°^ gave a history of perfect numbers and noted that 2^—1
can be factored if we find t such that m = 2pt-\-\ is a prime not dividing
8 = 1+2^+22^+ . . . +2^2'-^^^ since 2-p'-1= (2^-1)8 (mod m). Or we may
seek to express 2^—1 in two ways in the form x^—2y'.

On tables of exponents to which 2 belongs, see Ch. VII, Cunningham
and Woodam'^ Kraitchik.^-^

Additional Papers of a Merely Expository Character.

E. Catalan, Mathesis, (1), 6, 1886, 100-1, 178.

W. W. Rouse Ball, Messenger Math., 21, 1891-2, 34-40, 121.
- Pontes (on Bovnius^"), Mem. Ac. Sc. Toulouse, (9), 6, 1894, 155-67.

J. Bezdicek, Casopis Mat. a Fys., Prag, 25, 1896, 221-9.

Hultsch (on lamblichus), Nachr. Kgl. Sachs. Gesell., 1895-6.

H. Schubert, Math. Mussestunden, I, Leipzig, 1900, 100-5.

M. Nasso, Revue de math. (Peano), 7, 1900-1, 52-53.

i»*'Sphinx-Oedipe, 1913, 49-50.

i«*London Math. Soc, Records of Meeting, Dec, 1912, v-vi.

"«Quart. Jour. Math., 44, 1913, 274-7.

'"L'interm^diaire des math., 20, 1913, 78, 167.

"s/btd., 7-8, 149-150; cf. 140-1.

'"Proc. London Math. Soc, (2), 13, 1914, Records of meetings, xxxi.x. Bull. Amer. Math.

Soc, 20, 1913^, 531. Sphinx-Oedipe, 1914, 103-8.
20<>Sphinx-Oedipe, June, 1914, 85; I'interm^diaire des math., 24, 1917, 33.
-"Proc Indiana Acad. Science, 1914, 429-431.

2«Proc London Math. Soc, (2), 15, 1916, Records of meetings, Feb. 10, 1916, xxii.
»"Sphinx-Oedipe, 1909, 1-26.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AMICABLE NUMBERS. 33

G. Wertheim, Anfangsgriinde der Zahlentheorie, 1902.

G. Giraud, Periodico di Mat., 21, 1906, 124-9.

F. Ferrari, Suppl. al Periodico di Mat., 11, 1908, 36-8, 53, 75-6 (Cipolla).

P. Bachmann, Niedere Zahlentheorie, II, 1910, 97-101.

A. Aubry, Assoc, frang. avanc. sc, 40, 1911, 53-4; 42, 1913; Tenseignement

math., 1911, 399; 1913, 215-6, 223.
*M. Kiseljak, Beitrage zur Theorie der vollkommenen Zahlen, Progr. Agram,

1911.
*J. Vaes, Wiskundig Tijdschrift, 8, 1911, 31, 173; 9, 1912, 120, 187.
J. Fitz-Patrick, Exercices Math., ed. 3, 1914, 55-7.

Multiply Perfect Numbers.

A multiply perfect or pluperfect number n is one the sum of whose
divisors, including n and 1, is a multiple of n. If the sum is mn, m is called
the multiplicity of n. For brevity, a multiply perfect number of multi-
plicity m shall be designated by P^. Thus an ordinary perfect number is
a P2. Although Robert Recorde^^ in 1557 cited 120 as an abundant number,
since the sum of its parts is 240, such numbers were first given names and
investigated by French writers in the seventeenth century. As a P3 equals
one-half of the sum of its aliquot divisors or parts (divisors KPs), it was
called a sous-double; a P4 equals one-third of the sum of its aliquot parts
and was called a sous-triple; a P5 a sous-quadruple; etc.

F. Marin Mersenne proposed to R. Descartes^°^ the problem to find a
sous-double other than P^^^^ = 120 = 2^3-5. The latter did not react on the
question until seven years later.

Mersenne^"^ mentioned (in the Epistre) the problem to find a P4, a
P5 or a P^, a P3 besides 120, and a rule to find as many as one pleases. He
remarked (p. 211) that the P3 120, the P4 240 [for 30240?] and all other
abundant numbers can signify the most fruitful natures.

Pierre de Fermat^"- referred in 1636 to his former [lost] letter in which he
gave "the proposition concerning aliquot parts and the construction to
find an infinitude of numbers of the same nature." He^^^ found the second
P3, viz., P3<2) = 672 = 2^3-7.

Mersenne^°* stated that Fermat found the 1 3 7 15 . . .
P3 672 and knew infallible rules and analysis 2 4 8 16 . . .
to find an infinitude of such numbers. He^°^ 3 5 9 17 . . .
later gave [Fermat's] method of finding such P3: Begin with the geometric

'""Oeuvres de Descartes, 1, Paris, 1897, p. 229, line 28, letter from Descartes to Mersenne, Oct

or Nov., 1631.
^"iLes Preludes de I'Harmonie Universelle ou Questions Curiouses, Utiles aux Predicateurs, aux

Theologiens, Astrologues, Medecins, & Philosophes, Paris, 1634.
'•"Oeuvres de Fermat, 2, Paris, 1894, p. 20, No. 3, letter to Mersenne, June 24, 1636.
"^Oeuvres de Fermat, 2, p. 66 (French transl. 3, p. 288), 2, p. 72, letters to Mersenne and

Roberval, Sept., 1636.
'"Harmonic Universelle, Paris, 1636, Premiere Preface Generale (preceded by a preface of two

pages), imnumbered page 9, remark 10. Extract in Oeuvres de Fermat, 2, 1894, 20-21.
"'Mersenne, Seconde Partie de I'Harmonie Universelle, Paris, 1637. Final subdivision: Nou-

velles Observations Physiques et Math^matiques, p. 26, Observation 13. Extract in

Oeuvres de Fermat, 2, 1894, p. 21. ,

34 History of the Theory of Numbers. [Chap. I

progression 2, 4, 8, ... . Subtract unity and place the remainders above the
former. Add unity and place the sums below. Then if the quotient of
the (n+3)th number of the top line by the nth number of the bottom
line is a prime, its triple multiplied by the (n+2)th number of the middle
line is a P3. Thus if ?i = l, 15/3 is a prune and 3-5-8 = 120 is a P3. For
n = 3, 63/9 is a prime and 3-7-32 = 672 is a P3. [This rule thus states in
effect that 3-2"+2p is a P3 if p = (2'»+3-l)/(2"+l) is a prune.]

The third P3, discovered by Andr6 Jumeau, Prior of Sainte-Croix, is

P3^'^ = 523776 = 29311-31.

In April, 1638, he communicated it to Descartes^°^ and asked for the fourth
P3 (the fifth and last of St. Croix's challenge problems).

Descartes^*^^ stated that the rule ^^^ of Fermat furnishes no P3 other than
120 and 672 and judged that Fermat did not find these numbers by the
formula, but accommodated the formula to them, after finding them by trial.

Descartes^^^ answered the challenge of St. Croix with the fourth P3,

P3^'^ = 1476304896 = 2^33.1143.127.

Soon afterwards Descartes^ °^ announced the following six P4:

P4^i) = 30240 = 2^335.7,
P4(2) =32760 = 2^325.7.13,
P^^^^ = 23569920 = 2^335. 1 1 -31 ,
P4(*) = 142990848 = 2^327.11.13.31,
P4(^> = 66433720320 = 2^^335. 1 1 .43. 1 27,
P4^®^ =403031236608 = 2^3327.11.13.43.127,

and the sous-quadruple

Ps^^^ = 14182439040 = 2^3^5.7-11217.19.

He stated that his analysis had led him to a method which would require
time to explain in the form of a rule, but that he could find, for example,
a sous-centuple, necessarily very large.

Fermat apparently responded to the fifth challenge problem of St. Croix
on the fourth P3. Without warrant, Descartes^^" suspected that Fermat
had not found independently the fourth P3, but had learned from some one
in Paris of its earlier discovery by Descartes. Fermat^^^ indicated that he
possessed an analytic method by which he could solve all questions con-

'"^Oeuvres de Descartes, 2, Paris, 1898, p. 428, p. 167 (latter without name of St. Croix); cf.

Oeuvres de Fermat, 2, 1894, pp. 63-64.
"'Oeuvres de Descartes, 2, 1898, p. 148, letter to Mersenne, May 27, 1638.
^osQeuvres de Descartes, 2, 1898, 167, letter to Mersenne, June 3, 1638.
'"'Oeuvres de Descartes, 2, 1898, 2.50-1, letter to Mersenne, July 13, 1638. In June, 1645,

Descartes, 4, 1901, p. 229, again mentioned the first two of these Pt.
""Oeuvres de Descartes, 2, 1898, 273, letter to Mersenne, July 27, 1638.
"^Oeuvres de Fermat, 2, 1894, p. 165, No. 4; p. 176, No. 1; letters to Mersenne, Aug. 10 and

Dec. 26, 1638.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 35

cerning aliquot parts, apart from the testing of the primaUty of a number n,
knowing no method except the trial of each number < \/n as a divisor.
Descartes"^ gave the following rules for multiply perfect numbers:

I. If n is a P3 not divisible by 3, then 3n is a P4.
II. If a P3 is divisible by 3, but by neither 5 nor 9, then 45P3 is a P4.

III. If a P3 is divisible by 3, but not by 7, 9 or 13, then 3-7-13 P3 is a P4.

IV. If n is divisible by 2^ but by no one of the numbers 2^°, 31, 43, 127,

then 31n and 16-43-127n are proportional to the sums of their
aliquot parts.
V. If n is not divisible by 3 and if 3n is a P^k, then n is a Ps^.

By applying rule II to P3^^\ Ps^^\ P3^*^ Descartes obtained his P^^^^
P4<3^ P^^^K By applying rule III to Ps^'\ Ps^^\ Ps^''\ he obtained his

p (2) p (4) p (6)
^4 ) ^4 5 ^4 •

In the same letter, Descartes expressed to Mersenne a desire to know
what Frenicle de Bessy had found on this subject. Frenicle wrote direct
to Descartes, who in his reply^^^ expressed his astonishment that Frenicle
should regard as sterile the above rules for finding P4, since Descartes had
deduced by them six P4 from four P3, at a time when Mersenne had stated
to Descartes that it was thought to be impossible to find any at all. Des-
cartes stated that, since one can find an infinity of such rules, one has the
means of finding an infinitude of P^- From one of Frenicle's P5 (com-
municated to Descartes by Mersenne),

Ps^^) = 30823866178560 = 2i°3^5-72l3- 19-23-89,

Descartes (p. 475) derived the smaller P5:

Pg^^) = 31998395520 = 2^3^5.72.13.17.19.

Mersenne^^^ listed various P^ due to his correspondents, without cita-
tion of names. He listed the above Ps^'^ (^ = 1, 2, 3, 4) and remarked that
"un excellent esprit "^^^ found that when

P3^'^ = 459818240 = 2^5.7.19.37.73

is multiplied by 3, the product is a P4:

P4(^ = 2^3.5.7.19.37.73,

attributed to Lucas^^^ by Carmichael.^^^

"^Oeuvres, 2, 1898, 427-9, letter to Mersenne, Nov. 15, 1638.

"'Oeuvres de Descartes, 2, 1898, 471, letter to Frenicle, Jan. 9, 1639.

'"Les Nouvelles Pensees de Galilei, traduit d'ltalien en Frangois, Paris, 1639, Preface, pp. 6-7.

Quoted in Oeuvres de Descartes, 10, Paris, 1908, pp. 564-6, and in Oeuvres de Fermat, 4,

1912, pp. 65-66.
'"Frenicle de Bessy, according to the editors of the Oeuvres de Fermat, 2, 1894, p. 255, note 2;

4, 1912, p. 65, note 2 (citing Oeuvres de Descartes, 2, letter Descartes to Mersenne, Nov.

15, 1638, pp. 419-448 [p. 429]). It is clear that the discoverers Fermat, St. Croix, and

Descartes of the P|^*) (i = 2, 3,4) are not meant. It is attributed to Legendre"" by

Carmichael.*'*

36 History of the Theory of Numbers. [Chap, i

There are listed Descartes' six P^ and P^^^^ Frenicle's Ps^\ and also

P4^«) =45532800 = 2^3^5217.31,

P4^^^ = 43861478400 = 2^°3^5223.31.89,

and the erroneous P5 508666803200 (not divisible by 5^+5-|-l), probably
a misprint for the correct P5 (in the list by Lehmer^'^) :

P5^'^ = 518666803200 = 2^^3'5-72l3- 19-31 .

A part of these Pm, but no new ones, were mentioned by Mersenne^" in
1644; the least P3 is stated to be 120. (Oeuvres de Fermat, 4, 66-7.)
In 1643 Fermat^ ^^ cited a few of the P^ he had found:

Ps^^^ = 51001 180160 = 2^*5.7.19.31.151 ,

P4^'^) = 14942123276641920 = 2^3^5.17.23.137.547.1093,
P5(^) = 1802582780370364661760 = 22°335.72l32l9.31.61. 127.337,
Ps^®^ = 87934476737668055040 = 2^^3^5.7313. 19-37.73. 127,
Pg(i) = 223375374113133^7231.41.^1.241.307.467.2801,
Pg(2) = 22735537.11.13219.29.31.43.61.113.127.

He stated that he possessed a general method of finding all P^n-

Replying to Mersenne's query as to the ratio of

Pg(3) = 22^3^5^11.13219.31243.61.83.223.331.379.601.757

X 1201.7019.823543-616318177:100895598169

to the sum of its aUquot parts, Fermat^^^ stated that it is a Pq, the prime

factors of the final factor being 112303 and 898423 [on the finding of these

factors, see Ch. jXIV, references 23, 92, 94, 103]. Note that 823543 = 7^

Descartes^^^ constructed P3^2) = 572 = 21.32 by starting with 21 and
noting that (r(21) =32, o-(32) =63 = 3.21, for a defined as on p. 53.

Mersenne^^ noted that if a P3 is not divisible by 3, then 3P3 is a P4
[rule I of Descartes^^-]; if a P5 is not divisible by 5, then 5P5 is a Pq, etc.
He stated that there had been found 34 P4, 18 P5, 10 Pg, 7 P7, but no Pgso far.

In 1652, J. Broscius (Apologia,^* p. 162) cited the P4^'^ [of Descartes^"^].
The P3 120 and 672 are mentioned in the 1770 edition of Ozanam's'^
Recreations, I, p. 35, and in Hutton's translation of Montucla's^^ edition,
I, p. 39.

A. M. Legendre^^^ determined the Pm of the form 2"a/37 . . . , where a,
/3, 7, . . .are distinct odd primes, for 7n = 3, n^8; ?n=4, n = 3, 5; m = 5, n = 7.
No new P„ were found.

"*Oeuvres, 2, 1894, p. 247 (261), letter to Carcavi; Varia opera, p. 178; Pr^cia des oeuvres math,
de Fermat, par E. Brassinne, Toulouse, 1853, p. 150.

3'^Oeuvers de Fermat, 2, 1894, 255, letter to Mersenne, April 7, 1643. The editors (p. 256, note)
explained the method of factoring probably used by Fermat. The sum of the aliquot
parts of 23« is 223iV, where N = 616318177, and the sum of the aliquot parts of N is 2-7? M
iVf = 898423. As M does not occur elsewhere in Pe., it is to be expected as a factor of
the final factor of Pe.

"8Manuscript published by C. Henry, Bull. Bibl. Storia Sc. Mat. e Fis., 12, 1879, 714.

'^•Thor^ie des nombres, 3d ed., vol. 2, Paris, 1830, 146-7; German transl. by H. Maser, Leipzig,
2, 1893, 141-3. The work for n? =3 was reproduced by Lucas'^" without reference.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 37

E. Lucas^^o ga^g a table of P^ of the form 2''-\2''-l)N which includes
only 15 of the 26 Pm given above and no additional P^, m>2, except
two erroneous P5 :

2^°3^5-72.1l2.19.23.89, 2i^5-72l3.19237-73-127,

attributed elsewhere^^^ by him to Fermat. If we replace 7^ by 7 in the
former, we obtain a correct P5 listed by Carmichael 'P"^

P5(7> = 2'°3*5-7. 11219.23-89.

If in the second, we replace 5-7^ by 3^-5-7^ we obtain Fermat's P^-^K

A. Desboves^^^ noted that 120 and 672 are the only P3 of the form

2"-3-p, where p is a prime.

D. N. Lehmer^^^ gave the additional P„:

p^(i2) ^22325.7213.19,

P^(i3) = 2«3272l3.19237.73-127,

P5® =2213^527.19.23231.79.89.137.547.683.1093,

Pg(4) =2193^5^7211. 13.19.23.31.41. 137.547.1093,

Pg(5) =22^3^5.7211.13.17.19231.43.53.127.379.601.757.1801.

He readily proved that a P3 contains at least 3 distinct prime factors, a
P4 at least 4, a P5 at least 6, a Pq at least 9, a P^ at least 14.

J. Westlund324 proved that 2^3.5 and 2^3.7 are the only P3 of the form
V\'V2Vzy where the p's are primes and Pi<P2<P3. He^^^ proved that the
only P3 = Pi"p2P3P4, Pi<P2<P3<P„ is P3^'^ =293.11.31.

A. Cunningham^^^ considered P^ of the form 2^ \2^—l)F, where F is
to be suitably determined. There exists at least one such P^ for every q
up to 39, except 33, 35, 36, and one for g = 45, 51, 62. Of the 85 P^ found,
the only one published is the largest one, viz., for q = Q2, giving Pq^^^ with

F = 3^5'72ll. 13.19223.59.71.79.127.157.379.757.43331.3033169;

while none have m>6, and for m = 3 at most one has a given q. He found
in 1902 (but did not publish) the two P7 = 2^H2^^-1)P, where

F = C.192127 or 0.19^51-911,

C = 3i^-5^.7^.1M3.17-23.31-37-41.43.61.89.97-193.442151.

R. D. CarmichaeP^^ has shown that there exists no odd P^ with only
three distinct prime factors; that 2^3-5 and 2^3.7 are the only P^ with only

'20Bull. Bibl. e Storia Mat. e Fis., 10, 1877, 286. In 253-5-7, listed as a Pt, 3 is a misprint for 3».
'"Lucas, Theorie des Nombres, 1, Paris, 1891, 380. Here the factor 11^ IS^ of Fermat's P«(')

is given erroneously as lllS^, while the Pe^i^ of Descartes is attributed to Fermat.
'^Questions d'Algebre, 2d ed., 1878, p. 490, Ex. 24.
'^'Annals of Math., (2), 2, 1900-1, 103-4.
"^Annals of Math., (2), 2, 1900-1, 172-4.
'"Annals of Math., (2), 3, 1901-2, 161-3.
'"British Association Reports, 1902, 528-9.
'"American Math. Monthly, 13, Feb., 1906, 35-36.

717 8 5

38 History of the Theory of Numbers. [Chap, i

three distinct prime factors ;^^^ that those with only four distinct prime fac-
tors are^^" the P^^^^ of St. Croix^"^ and the P4^'^ of Descartes f°^ and that the
even P„ with five^^^ distinct prime factors are P3^^\ Pi^\ Pi^^ of Des-
cartes^"^' ^"^ and P^^^^ of Mersenne.^"

CarmichaeP^^'* stated and J. Westlund proved that if n>4, no P„ has
only n distinct prime factors.

Carmichael's^^^ table of multiply perfect numbers contains the misprint
1 for the final digit 0 of Descartes' Pi^\ and the erroneous entry 919636480
in place of its half, viz., P^-^^ of Mersenne.^^^ The only new P^ is

Pg(7) = 2^^3^527211. 13-17.19-3143.257.

All P,;,< 10^ were determined; only known ones were found.
CarmichaeP^^ gave an erroneous P5 and the new P^:

p^(i4)^2"3272l3-1923M27.151,

p^(i5)^2253^52l9-31.683.2731-8191,

p^(i6)^225365-19-23-137-547-683-1093-2731-8191.

Carmichael and T. E. Mason^^ gave a table which includes the above
hsted 10 P2, 6 P3, 16 P4, 8 P5, 7 Pq, together with 204 new multiply perfect
numbers P, (i = 3, . . . , 7) . Of the latter, 29 are of multiplicity 7, each
having a very large number of prime factors. No P7 had been previously
published.

[As a generalization, consider numbers n the sum of the kth. powers of
whose divisors < n is a multiple of n. For example, n = 2p, where p is a
prime 8/1 ±3 and k is such that 2*^+1 is divisible by p; cases are p = 3,
k = l; p = 5, k = 2; p = ll, k = 5; p = 13, A; = 6.]

Amicable Numbers.

Two numbers are called amicable* if each equals the sum of the aliquot
divisors of the other.

According to lamblichus^ (pp. 47-48), "certain men steeped in mistaken
opinion thought that the perfect number was called love by the Pythago-
reans on account of the union of different elements and affinity which exists
in it; for they call certain other numbers, on the contrary, amicable num-
bers, adopting virtues and social quahties to numbers, as 284 and 220, for
the parts of each have the power to generate the other, according to the rule
of friendship, as Pythagoras affirmed. WTien asked what is a friend, he
replied, 'another I,' which is shown in these numbers. Aristotle so defined
a friend in his Ethics."

«»Aimalsof Math., (2), 7, 1905-6, 153; 8, 1906-7, 49-56; 9, 1907-8, 180, for a simpler proof that

there is no Pa = Pi^p^Vi^t c> 1.
""Annals of Math., (2), 8, 1906-7, 149-158.

"'Bull. Amer. Math. Soc, 15, 1908-9, pp. 7-8. Fr. transl., Sphinx-Oedipe, Nancy, 5, 1910, 164-5.
wi^Amer. Math. Monthly, 13, 1906, 165.

»«Bull. Amer. Math. Soc, 13, 1906-7, 383-6. Fr. transl., Sphinx-Oedipe, Nancy, 5, 1910, 161-4.
»"Sphinx-Oedipe, Nancy, 5, 1910, 166.
»"Proc. Indiana Acad. Sc, 1911, 257-270.
*Amiable, agreeable, befreundete, verwandte.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AMICABLE NUMBERS. 36

In the ninth century the Arab Thabit ben Korrah^° (prop. 10) noted that
2'*/i^ and 2"s are amicable numbers if

(1) /i = 3-2"-l, f=3-2"-i-l, s = 9'2^''-'-l

are primes > 2, literally, if

/l = 2+2^ t = z-2''-\ 3 = H-2+...+2^ s = (2"+^+2'*-2)2''+^-l.

The term used for amicable numbers was se invicem amantes. In the article
in which F. Woepcke^'^ translated this Arabic manuscript into French, he
noted that a definition of these numbers, called congeneres, occurs in the
51st treatise (on arithmetic) of Ikhovan Algafa, manuscript 1105, anciens
fonds arabes, p. 15, of the National Library of Paris.

Among Jacob's presents to Esau were 200 she-goats and 20 he-goats,
200 ewes and 20 rams (Genesis, XXXII, 14). Abraham Azulai^^^ (1570-
1643), in commenting on this passage from the Bible, remarked that he had
found written in the name of Rau Nachshon (ninth century A. D.): Our
ancestor Jacob prepared his present in a wise way. This number 220 (of
goats) is a hidden secret, being one of a pair of numbers such that the parts
of it are equal to the other one 284, and conversely. And Jacob had this in
mind; this has been tried by the ancients in securing the love of kings and
dignatories.

Ibn Khaldoun^^° related "that persons who have concerned themselves
with talismans affirm that the amicable numbers 220 and 284 have an
influence to establish a union or close friendship between two individuals.
To this end a theme is prepared for each individual, one during the ascend-
ency of Venus, when that planet is in its exaltation and presents to the
moon an aspect of love or benevolence; for the second theme the ascendency
should be in the seventh. On each of these themes is written one of the
specified numbers, the greater (or that with the greater sum of its aliquot
parts?) being attributed to the person whose friendship is sought."

The Arab El Madschriti,^^! or el-Magriti, (flOOT) of Madrid related that
he had himself put to the test the erotic effect of ''giving any one the
smaller number 220 to eat, and himself eating the larger number 284."

Ibn el-Hasan^"'' (tl320) wrote several works, including the "Memory
of Friends," on the explanation of amicable numbers.

Ben Kalonymos^^^^ discussed amicable numbers in 1320 in a work
written for Robert of Anjou, a fragment of which is in Munich (Hebr. MS.
290, f. 60). A knowledge of amicable numbers was considered necessary
by Jochanan Allemanno (fifteenth century) to determine whether an
aspect of the planets was friendly or not.

^^^Baale Brith Abraham [Commentary on the Bible], Wilna, 1873, 22. Quotation suppUed by

Mr. Ginsburg.
'^oProlegomenes hist. d'Ibn Khaldoun, French transl. by De Slane, Notices et Extraits des

Manuscrits de la Bibl. Imperiale, Paris, 21, I, 1868, 178-9.
"^'Manuscript Magriti; Steinschneider, Zur pseudoepigraphischen Literatur inbesondere der

geheimen Wissenschaften des Mittelalters, Berlin, 1862, p. 37 (cf. p. 41).
'""H. Suter, Abh. Gesch. Math. Wiss., 10, 1900, 159, § 389.
»"*Hebr. Bibl., VII, 91. Steinschneider, Zeitschrift der Morgenlandischen Ges., 24, 1870, 369.

5

11

23

47

2

4

8

16

6

12

24

48

71

287

1151

40 History of the Theory of Numbers. [Chap, i

Alkalacadi,^" a Spanish Arab (tl486), showed the method of finding the
least amicable numbers 220, 284.

Nicolas Chuquet^^ in 1484 and de la Roche^^ in 1538 cited the amicable
numbers 220, 284, "de merueilleuse familiarite lung auec laultre." In 1553,
Michael StifeP^ (folios 26v-27v) mentioned only this pair of amicable num-
bers. The same is true of Cardan, ^^ of Peter Bungus^- (Mysticae numerorum
signif., 1585, 105), and of TartagUa.^^ Reference may be made also to
Schwenter."

In 1634 Mersenne^"^ (p. 212) remarked that "220 and 284 can signify
the perfect friendship of two persons since the sum of the aliquot parts of
220 is 284 and conversely, as if these two numbers were only the same thing."

According to Mersenne's^"^ statement in 1636, Fermat^^ found the
second pair of amicable numbers

17296 = 2'.23.47, 18416 = 2^-1151,

and communicated to Mersenne^°^ the general rule: Begin with the geo-
metric progression 2, 4, 8, ... , write the prod-
ucts by 3 in the line below; subtract 1 from
the products and enter in the top row. The
bottom row is 6-12-1, 12-24-1,. . .When a
mmiber of the last row is a prime (as 71) and
the one (11) above it in the top row is a prime,

and the one (5) preceding that is also a prime, then 71.4 = 284, 5-11-4 = 220
are amicable. Similarly for

1151-16 = 18416, 23-47-16 = 17296,

and so to infinity. [The rule leads to the pair 2"/i<, 2'*s, where h, t, s are
given by (1).]

Descartes^^^ gave the rule: Take (2 or) any power of 2 such that its
triple less 1, its sextuple less 1, and the 18-fold of its square less 1 are all
primes;* the product of the last prime by the double of the assumed power
of 2 is one of a pair of amicable numbers. Starting with the powers 2, 8, 64,
we get 284, 18416, 9437056, whose aliquot parts make 220, etc. Thus the
third pair is

9363584 = 2^-191-383, 9437056 = 2"-73727.

Descartes^^^ stated that Fermat's rule agrees exactly with his own.

Although we saw that Mersenne quoted in 1637 the rule in Fermat's
form and expressly attributed it to Fermat, curiously enough Mersenne^ ^^
gave in 1639 the rule in Descartes' form, attributing it to "un excellent
Geometre" (meaning without doubt Descartes, according to C. Henry^"),

''^Manuscript in Biblioth^que Nationale Paris, a commentary on the arithmetic Talkhys of
Ibn Albanna (13th cent.). Cf. E. Lucas, L'arithm^tique amusante, Paris, 1895, p. 64.

'"Quesiti et Inventione, 1554, fol. 98 v.

'^♦Oeuvres de Fermat, 2, 1894, p. 72, letter to Roberval, Sept. 22, 1636; p. 208, letter to Frenicle,
Oct. 18, 1640.

»^euvre8 de Descartes, 2, 1898, 93-94, letter to Mersenne, Mar. 31, 1638.
•Evidently the numbers (1) if the initial power of 2 be 2""^

"•Oeuvres de Descartes, 2, 1898, 148, letter to Mersenne, May 27, 1638.

"'Bull. Bibl. Storia So. Mat. e Fis., 12, 1879, 523.

Chap. I) PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 41

and derived as did Descartes the first three pairs of amicable numbers from
2, 8, 64. We shall see that various later writers attributed the rule to
Descartes.

Mersenne^^ again in 1644 gave the above three pairs of amicable num-
bers, the misprints in both^^^ of the numbers of the third pair being noticed
at the end of his book, and stated there are others innumerable.

Mersenne®^ in 1647 gave without citation of his source the rule in the
form 2-2% 2-2"/i<, where 1 = 3-2'' -1, h = 2t+l, s = ht+h-i-t are primes
[as in (1)].

Frans van Schooten,^^^ the younger, showed how to find amicable
numbers by indeterminate analysis. Consider the pair 4a:, 4yz [x, y, z odd
primes]; then

7+3a: = 4i/0, 7-\-7y+7z+Syz = 4x.

Eliminating x, we get 2 = 34-16/(2/ — 3). The case ^ = 5 gives 2;= 11, ^' = 71,
yielding 284, 220. He proved that there are none of the type 2x, 2yz, or
8x, Syz, and argued that no pair is smaller than 284, 220. For 16.x, 16yz,
he found 2=15-l-256/(i/ — 15), which for y = 47 yields the second known
pair. There are none of the type 32a;, S2yz, or type 64a:, Myz. For 128a:,
1281/2, he got 2= 127-^16384/(1/ -127), which for 2/ = 191 yields the third
known pair. Finally, he quoted the rule of Descartes.

W. Leyboum^^ stated in 1667 that ''there is a fine harmony between
these two numbers 220 and 284, that the aliquot parts of the one do make
up the other . . . and this harmony is not to be found in many other numbers."

In 1696, Ozanam''^ gave in great detail the derivation of the three known
pairs of "amiable" numbers by the rule as stated by Descartes, whose name
was not cited. Nothing was added in the later editions.'^' ^^

Paul Halcke^^" gave Stifel's^^ rule, as expressed by Descartes.^^^

E. Stone^^^ quoted Descartes' rule in the incorrect form that 2^''pq and
3-2"p are amicable if p = 3-2'*— 1 and g = 6-2'*— 1 are primes.

Leonard Euler^^^ remarked that Descartes and van Schooten found only
three pairs of amicable numbers, and gave, without details, a fist of 30 pairs,
all included in the later paper by Euler.^^^

G. W. Kraft^^^ considered amicable numbers of the type APQ, AR,
where P, Q, R are primes not dividing A. Let a be the sum of all the divi-
sors of A . Then

R+1 = {P+1){Q+1), {R-{-l)a = APQ-^AR.

Assuming prime values of P and Q such that the resulting R is prime, he
sought a number A for which A /a has the derived value. For P = 3, Q = 1 1 ,

"'Not noticed in the correction (left in doubt) in Oeuvres de Fermat, 4, 1912, p. 250 (on pp.

66-7). One error is noted in Broscius*^, Apologia, 1652, p. 154.
"'Exercitationum mathematicarum libri quinque, Ludg. Batav., 1657, liber V : sectiones triginta

miscellaneas, sect. 9, 419-425. Quoted by J. Landen.*^
""Deliciae Mathematicae, oder Math. Sinnen-Confect, Hamburg, 1719, 197-9.
*"New Mathematical Dictionary, 1743 (under amicable) .
"'De numeria amicabilibus. Nova Acta Eruditorum, Lipsiae, 1747, 267-9; Comm. Arith. Coll.,

II, 1849, 637-8.
-•»Novi Comm. Ac. Petrop., 2, 1751, ad annum 1749, Mem., 100-18.

42 History of the Theory of Numbers. [Chap, i

then A:a = S:5; he took A = 3B, S^B, 3^5, but found no solution. For
p = 5, Q = 41, we have 72 = 251, 38A = 21a; set A = 495, whence 3-576 =
38-75, where b is the sum of the divisors of B; set B = 9C, whence C:c =
13:14, C=13, yielding the amicable numbers 5-41A., 251A, where
A = 3^-7213 = 5733 [the pair VII in Euler's^'^^ ijgt and (7) in the table below].
Again, to make A/a = 3/8, set A = 35, whence a = 46 and the condition is
6 = 25, whence 5 is a perfect number prime to 3. Using 5 = 28, we get
A = 84. For use in such questions, Kraft gave a table of the sum of the
divisors of each number^ 150. He quoted the rule of Descartes.

L. Euler^*^^ obtained, in addition to two special pairs, 62 pairs [including
two false pairs] of amicable numbers of the type am, an, in which the
common factor a is relatively prime to both vi and n. He wrote jm for
the sum of all the divisors of m. The conditions are therefore

jm=jn, fa-jm = a{m-{-n).

If m and n are both primes, then 7n = n and we have a repeated perfect
number. Euler treated five problems.

(1) Euler's problem 1 is to find amicable numbers apq, ar, where p, q, r,
are distinct primes not dividing the given number a. From the first con-
dition we have r = xy — \, where x — p-\-\, y = q-\-\. From the second,

xyi a = a{2xy —x — y).

Let a/{2a— \a) equal 6/c, a fraction in its lowest terms. Then

y = bx/{cx — b), {cx — b){cy — b)=b^.

Thus x and y are to be found by expressing 6^ as a product of two factors,
increasing each by 6, and dividing the results by c.

(li) Fu-st, takea = 2". Then6 = 2^ c=l, x, 2/ = 2"**+2^ Letri-A; = m.
Then

p = 2"»(22*=+2*)-l, g = 2'"(l+2*)-l, r = 2^"'(2^''+^+2^''+2'')-l.

When these three are primes, 2"*"^^'^^ and 2'"''"^ are amicable. Euler noted
that the rule communicated by Descartes to van Schooten is obtained by
taking A:= 1, and stated that 1, 3, 6 are the only values ^ 8 of m which yield
amicable numbers (above^^^). For k = 2 or 4, Euler remarked that r is
divisible by 3; for k = 3, vi<Q, and for k = 5, mS2, p, q, or r is composite.

(I2) Take a = 2J, where /=2"+^+e is a prune. Then 2a-fa = e+l.
If e+1 divides a, we have c = l. Set e+ 1 = 2^, A;^?n, n = m+A:. Then

/=2*(2'"+^ + l)-l, a = 2"'+i, 6 = 27, b""={x-b){y-b).

For k = l, /=2'"+2+l is to be a prime, whence m+2 is a power of 2.
If w = 0, 6=/=5, and either x = y, p = q; or x, y = Q,30; p, q = 5, 29, whereas
p and q are to be distinct and prime to 10. If m = 2, /=17, 68^ is to be
resolved into distinct even factors; in the four resulting cases, p, q, r are

'"De numeris amicabilibus, Opuscula varii argumenti, 2, 1750, 23-107, Berlin; Comm. Arith., 1,
1849, 102-145. French transl. in Sphinx-Oedipe, Nancy, 1, 1906-7, Supplement
I-LXXVI.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AMICABLE NUMBERS. 43

not all prime. In the next case w = 6, /=257, Euler examined only the
case* x — 6 = 2^-257, finding q composite.

For A; = 2, Euler excluded m = 1, 3 [m = 4 is easily excluded].

(13) For k^n in (I2), 0 = 2*", where m = k—n. Then

6 = 2"+i+2"'+"-l=/
must be a prime. Thus we must take as the factors of 6^

2'"x-6 = l, 2"'2/-fe = 62,

whence z = 2" +2"+^"'", y-=hx. If m = 1, one of

/=2'»+2-l, p = 2^+'-l

has the factor 3 and yet must be a prime; hence n=l, g = 27. If m = 2,
Euler treated the cases n^5 and found (for n = 2) the pair (4) of the table.
[For 6^n^l7, / or p is composite.] For m odd and >1, / or p has the
factor 3. For m = 4, n^ 17, no solution results.

(14) For a = 2"(gr— l)(/i — 1), where the last two factors are prime, set
d = 2a-fa. Then

ig - 2^*+^) {h - 2^^+^) =d- 2"+^ + 2^""+^
Euler treated the cases n^3, d = 4, 8, 16, finding only the pair (9).

(15) Special odd values of a led (§§56-65) to seven pairs (5)-(8),
(11)-(13). The cases a = 3^.5, 32-72-13-19 were unfruitful.

(2) Euler's problem 2 is to find amicable numbers apq, ars, where p, q,
r, s are distinct primes not dividing the given number a. Since jP'j2
— ['>''] s, we may set

p = ax — l, q = ^y — l, r = /3x — 1, s = ay — l.

We set fa:a = 2b—c:h, where b and c are relatively prime. The second
condition fa- fpq = a{pq+rs) gives

ca/3x2/ = 6(a+iS) (x+2/) -26.
Multiply it by ca^. Then

[ca^x-h{a+^)][ca^y-b(a+^)] = h\a+^y-2hca^.
Given a, ^, a and hence b, c, we are to express the second member as a prod-
uct of two factors and then find x, y.

For a = l, i3 = 3, 0 = 2^ Euler obtained the pairs (a), (28). For a = 2,
^ = 3, a = 32-5-13, he got (32); for a = l, /3 = 4, a = 3^-5, (30). The ratio a:^
may be more complex, as 5 :21 or 1 :102, in (7). As noted by K. Hunrath,^^^*
the numbers (7) are not amicable. Nor are the ratios as given, although
these ratios result if we replace 8563 by 8567 = 13-659. This false pair
occurs as XIII in Euler's^^^ list.

(3) Problem 3 is derived from problem 2 by replacing s by a number /
not necessarily prime. Let h be the greatest common divisor of ff=hg
andp+l = ^x. Thenr-{-l=xy, q-{-l = gy. Also

ghxyfa=f{afr)=a(pq+fr)^a\{hx-l){gy-l)+f{xy-l)\.

*A11 the remaining cases are readily excluded.
"♦"BibUotheca Math., (3), 10, 1909-10, 80-81.

44 History of the Theory of Numbers. [Chap, i

Multiply by 6/a and replace bja by 2ab — ac [see case (1)]. Thus
exy — bhx — hgy = b{f—l), e=bf—bgh-{-cgh.

Thus L^b'^gh+be{f—l) is to be expressed as the product PQ of two factors
and they are to be equated to ex—bg, ey — bh. The case a = 2 is unfruitful.
(3i) Let a = 4. Then 6 = 4, c = l, e = 4/— 3^/i. The case/= 3 is excluded
since it gives e = 0. For/ =5, g = 2, h = S, we again get (a) and also (j3).
For/=5, ^ = 1, h = 6, we get only the same two pairs. For a prime /^ 7,
no new solutions are found. For /= 5-13, (51) results.

(32) Let a = 8, whence 6 = 8, c = L The cases /= 11, 13 are fruitless,
while /= 17 yields (16). The least composite/ yielding solutions is 11-23,
giving (44), (45), (46). This fruitful case led Euler to the more convenient
notations (§88) M = hP, N = gQ, L = PQ. The problem is now to resolve
L ff into two factors, Af , N, such that

M+bff N+bff

are integers and primes, while in r+1 = {p+l){q+l)/jf, r is a prime.

(33) Let a = 16. For/=17, we obtain the pairs (21), (22); for/=19,
(23); for/=23, (17), (19), (20); for/=47, (18); for/= 17-167, (49). Cases
/=31, 17-151 are fruitless [the last since 129503 has the factor 11, not
noticed by Euler].

(34) For a = 3^-5 or 32.7-13, 6 = 9, c = 2; the first a with/=7 yields (30).

(4) Problem 4 relates to amicable numbers agpq, ahr, where p, q, r are
primes. Eventually he took also g and h as primes. We may then set
g-\-l — km, h-\-\ = kn. For m = \, n = 3, a = 4 or 8, no amicables are found.
Form = 3, n = l, the cases a =10, A: = 8 and a = 3^-5, ^' = 8, yield (38), (55).

(5) Euler's final problem 5 is of a new type. He discussed amicable
numbers zap, zbq, where a and 6 are given numbers, p and q are unknown
primes, while z is unknown but relatively prime to a, 6, p, q. Set
JoM 6 = m:n, where m and n are relatively prime. Since(p-fl)j a = (54-l)j6,
we may set p-\-\=^nx, q-{-\=mx. The usual second condition gives

r r / K 7 / ^ — nxfa

nx\a'{z = za{nx — l)-j-zb{mx — l), C —-, 1^ r*

■^ -^ j^ {na-\-mb)x — a — b

Let the latter fraction in its lowest terms be r/s. Then z = kr, jz = k$.
Since f{kr)'^kCr, we have s'^ff. Hence we have the useful theorem:
if z:Cz = r':s', s'<\r', then r' and s' have a common factor > 1.

(5i) The unfruitful case a = 3, 6 = 1, was treated like the next.

(52) Let 0 = 5, 6=1, whence w = 6, n = l, 2:J z = 6a::llx — 6. By the
theorem in (5), x must be divisible by 2 or 3. Euler treated the cases
x = 3(3^+1), x = 2{2t+\). But this classification is both incomplete and

Chap. I] PERFECT, MULTIPLY PERFECT, AND AMICABLE NUMBERS.

45

overlapping. Since p = x — l is to be prime, x is even (since a; = 3 makes z
divisible by p = 2) . Hence x = 2P,z:fz = QiP:llP—S. By the theorem in (5) ,
QP and IIP — 3 have a common factor 2 or 3, so that P is either odd or divis-
ible by 6. For P = Ql, the ratio is that of 126 to 22Z — 1 , which as before must
have the common factor 3, whence l = 3t-\-l. Then z:fz = 4:{St-{-l) :22t-\-7,
a ratio of relatively prime numbers, whence 22t+7'^f 4(31+1), and
hence t = 2k, k = 0 or k>3. For A; = 0, we obtain the pair 220, 284.
The next value >3 of A; for which p = x — l and q = Qx—l are primes is
k = Q, giving p = 443, g = 2663, numbers much larger than those in the
(unnecessary) cases treated by Euler. Then z:jz = 4-37:271; set z = S7''d,
d not divisible by 37; the cases e = 1, 2, 3 are excluded by the theorem in (5).
For the remaining case P odd, P = 2Q-\-l, Euler treated those values ^100
of Q, and also Q = 244, for which p and q are primes and obtained the pair
in (I3), two pairs in (I5), and (14), (15).

(53) Euler treated in §§112-7 various sets a, b, and obtained (a) and nine
new pairs given in the table.

In the following table of the 64 pairs of amicable numbers obtained by
Euler, the numbering of any pair is the same as in Euler's list, but the pairs
have been rearranged so that it becomes easy to decide if any proposed
pair is one of Euler's. As noted by F. Rudio,^^^'' (37) contained the mis-
print 3^ for 3^, w^hile (7) and (34) are erroneous, 220499 being composite
(311-709); he checked that all other entries are correct.

(4) 22-23{^27^^

(9) 2M3.17{3||09

(47) 23/11-29-239
^*'^ "^ 1191449

^4»; ^ \29-47-59

(21) 2417'5119

(^)2^{83lo39(f-l««)

(18) 2^{i:?^

(27) o«/79- 11087
^^^^ ^ \383-2309

(37) s^-sgi'ig''

(15) 32.7-13-4M63<
(35) 32.5.19{7^227

5-977
5867

(38) 2-5{7:

(a)22

60659
23-29-673
5-131
17-43

^•' ^ 1647-719

(43) 2'
(60)

11-59-173
47-2609
2^-19-41
26-199
(oo\ 94/17-10303

(2) 2^

[23-47
\1151

(19) 2^{i:t2?

(25) 2»P-12671
K^Q) z ^227-2111

,3. 27/191-383

(5) 32-7-13[

(14) 32-72-13-97

5-17
107

5193
1163

(8) 3^-5-7{i?2S

251
107

(1) 22{^jll

i3) 2^(^32

,45. 23(ll-23-1871
V4^) ^ \467-1151

.4Q. 23/11-163-191
^4u; z 131.11807

,r.,. /23-41-467
^^^1 \25-19-233

(23) 2^{}9gl439

(50) 2423-47-9767
\tM) z |i583.7io3

,17s 24/23-1367
^^'^ "^153-607

(26) 2^{^|JJ^f

/90X r,8/383-9203
K^-6) z |ii5i.3067

(7) 32-72-13{|5Y
(10) 32-5- 19-37 (710^
(6) 3^-5-13gl9l9

(51) 2^^^^

•131187
-2267
(29) 2^-ll{17:263

,,,. 23/11-23-2543
^**^ ^ 1383-1907

(16) 2^(M:^^

(49) 24/17-167-13679
KV6) z I809.51071

(36) 2^-67{|72411

.24) 26/59-1103
(.Z4J L J79.827

{b2)Z^-l-\Z^^lll]f

'"^Bibliotheca Math., (3), 14, 1915, 351-4.

46 History of the Theory of Numbers. [Chap, i

(31) S^-5'13{ll:]f (54) 3«.5^{}1:^9.179 ^g^ ^,_^_^^,^^l29.5m

(33) 33.5.13.19^/2711 (32) 3^-5-13{^^:^J (12) S^.r-lVlsl^lf^^'

(41)33.7.13.23|JJ;1%367 ^g^^ 3,.-,. ^g.^gjl 1-220499 ^^^^^^

(30) 33.5{[7^1j (55) ■S^-5{',lll%^ (42) 33.5.23(11 -.J^SIT

(11) 3^.5.1l{29g89 (56) 3^.7.11M9{g97019 (57)3^.7.11M9{^3^6959^

(53) 3».7M3.53{ll4211 (53) 3s.7M3.19{4™19 (59^ 3^.7M3.19{53g6959^

Euler's final list of 61 pairs did not include the pairs a, jS, 7, although he
had obtained a four times in the body of his paper, viz., in (2), (3i), (63);
jS twice in (3i); 7 in (2). Moreover, these three unlisted pairs occur as
VIII, IX, and XIII among the 30 pairs in Euler's^^^ earlier list, a fact noted
on p. XXVI and p. LVIII of the Preface by P. H. Fuss and N. Fuss to
Euler's Comm. Arith. Coll., who failed to observe that these three pairs
occur in the text of Euler's present paper. Nor did these editors note
that the fourth mentioned case of divergence between the two lists is due
merely to the misprint^^^'' of 57 for 47 in (43) of the present list, so that
the correctly printed pair XXVIII of the list of 30 is really this (43) and
not a new pair, as supposed by them.

From the fact that Euler obtained in his posthumous tract®^ on amicable
numbers the pairs a, jS (once on p. 631 and again on p. 633 and finally on
p. 635), the editors inferred, p. LXXXI of the Preface, that the tract differs
in analysis from the long paper just discussed. But no new pairs are found,
while the cases treated on pp. 631-2 are merely problems 1 and 2 of Euler's
preceding paper. It is different with p. 634, where Euler started with two
numbers like 71 and 5-11 which, by his table, have the same sum, 72, of
divisors, and required a number a relatively prime to them such that 71a
and 55o are amicable. The single condition is 72J a=(71+55)o, whence
ja:a = 7A. Thus a has the factor 4. If a = 46, where b is odd, then
Ch = h = l, and the pair 284, 220 results. The case a = 86 is impossible. This
method was used in a special way by Kraft^^^ who limited the numbers
from which one starts to a prime and a product of two primes.

In the Encyclopedie Sc. Math., I, 3i, p. 59, note 320, it is stated that this
posthumous tract contains four pairs not in Euler's list of 61, two pairs being
those of Fermat^^^ and Descartes.^^^ But these were fisted as (2) and (3)
by Euler and were obtained by him in case (li) and attributed to Descartes.

E. Waring^^^ noted that 2'*x, 2''yz are amicable if

2"'?/z_2"+^ + l 2^"

2"-l ' i/-2"+l

where x^ y, z are primes and ?/ — 2"H-1 divides 2^**. He cited the first two
such pairs of amicable numbers.

3"«G. Enestrom, Bibliotheca Math., (3), 9, 1909, 263.
3«*Meditationes algebraicae, 1770, 201; ed. 3, 1782, 342-3.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 47

The first three pairs were given in an anonymous work.^^®

In 1796, J. P. Gruson^°° (p. 87) gave the usual rule (1) leading to the
three first known amicable pairs (verwandte Zahlen).

A. M. Legendre^^^ attributed the rule (1) to Descartes.

G. S. KliigeP^^ gave a process leading to the choice of P and Q, left
arbitrary by Kraft.^^^ ^^ ^ave A:a = R+l:PQ-\-R = 2R-P-Q. Thus
P-(-Q= \R{2A—a)—a\ /A, while PQ is given by Kraft's second equation.
Hence P and Q are the roots of a quadratic equation. For example, if

A = 4, then

8P, SQ = R-7±VR^-Q2R-QS.

The positive root of a;^ — 62a: — 63 = 0 lies between 60 and 61. Thus we
try primes ^ 61 for R, such that i^ — 7 is divisible by 8. The first available
R is 71, giving P=ll, Q — 5 and the amicable pair 220, 284. In general,
the quantity a^R^+2^R-\-y under the radical sign can be made equal to the
square of ai^+P ip arbitrary) by choice of R.

John Gough^^^ considered amicable numbers ax, ayz, where x, y, z are
distinct primes not dividing a. Let q be the sum of the aliquot divisors

of a. Then

a+q-\-qx = ayz, x+l = {y+l){z+l).

If q^a/i, the first gives ayz< (l+a:)a/4, while 2y-2z>x-\-l by the second,
Thusg'>a/4. Let a = r", where r is a prime > 1 . Then Q'=(a — l)/(r' — 1),
which with g>a/4 implies a(5— r)>4, r = 2 or 3. He proved that Tt^S.
whence r = 2, the case treated by van Schooten.^^^

J. Struve^^^ cited his Osterprogramm, 1815, on amicable numbers.

A. M. Legendre^^° discussed the amicable numbers of the type (li) of
Euler^^^ (with Euler's m, k replaced by m—iJi,,fx). Legendre noted that
r = 2^'""''^ (2*^+1)^ — 1 is of the form s^ — 1 and hence composite, if k is even;
also that, if A: = 3, p = 9-2'"+3-l, g = 9-2"'-l, one of which is of the form
s^ — 1. He considered the new case k = 7 and found for m = l that p = 33023,
q = 257, r = 8520191, stating that if r be a prime we have the amicable num-
bers 2^pq, 2V. This is in fact the case.^^^ For ^ = 1, we have the ancient
rule (1); he proved that for n^l5 it gives only the known three pairs of
amicable numbers.

Paganini^'^^, at age 16, announced the amicable numbers 1184 = 2^37,
1210 = 2.5.11"^, not in the list by Euler^^'*, but gave no indication of the
method of discovery.

^^'EncyclopMie methodique. . .Amusemens des Sciences Math, et Phys., nouv. 6d., Padoue,
1793, I, 116. Cf. Les amusemens math., Lille, 1749, 315.

»"Th6orie des nombres, 1798, 463.

«8Math. Worterbuch, 1, 1803, 246-252 [5, 1831, 55].

«»New Series of the Math. Repository (ed., Th. Leyboum), vol. 2, pt. 2, 1807, 34-39. He cited
Button's Math. Diet., article Amicable Numbers, taken from van Schooten^^'.

""Theorie des nombres, ed. 3, 1830, II, §472, p. 150. German transl. by H. Maser, Leipzig,
1893, II, p. 145.

"iTchebychef, Jour, de Math., 16, 1851, 275; Werke, 1, 90. T. Pepin, Atti Ace. Pont. Nuovi
Lincei, 48, 1889, 152-6. Kraitchik, Sphinx-Oedipe, 6, 1911, 92. Also by Lehmer's Fac-
tor Table or Table of Primes.

'"B. Nicol6 I. Paganini, Atti deUa R. Accad. Sc. Torino, 2, 1866-7, 362. Cf. Cremona's Ital.
transl. of Baltzer's Mathematik, pt. III.

48 History of the Theory of Numbers. (Chap, i

P. Seelhoff^^^ treated Euler's^^ problems 1 and 2 by Euler's methods
(though the contrary is implied), and gave about 20 pairs of amicable
numbers due to Euler, with due credit for only three pairs. The only new-
pairs (pp. 79, 84, 89) are

Q2721Q in oQf83-1931 ^ef 139-863

6 i A^-Ay'^'^|i62287 "^1167.719.

E. Catalan^^^ stated empirically that if ??i is the sum of the divisors
<n of n, and n2 is the sum of the divisors <ni of ?ii, etc., then n, nj, n2, . . .
have a limit X, where X is unity or a perfect number.

J. Perrott"^ [Perott] noted that there is no limit for n = 220, since

^1 = 713= . . . =284, n2 = n4= . . . =220.

H. LeLasseur^^*^ found that for n< 35 the numbers (1) are all odd primes,
and hence give amicable numbers, only when n = 2, 4, 7.

Josef Bezdicek^^^ gave a translation into Bohemian of Euler,^^ without
credit to Euler, and a table of 65 pairs of amicable numbers.

Aug. Haas"^ proved that, if M and A^ are amicable numbers,

l/S-+l/si=l,
m n

where m and n range over all divisors of M and iV, respectively. For,

2w = Sn = M+iV, so that

m~ M ~ M ' n~ N ~ N

If M = N, N is perfect and the result becomes that of Catalan. ^"'^

A. Cunningham^'^ considered the sum s{n) of the divisors <n of ?i and
wrote s^{n) for s]s(??)}, etc. For most numbers, s^(n) = l when A; is suffi-
ciently large. There is a small class of perfect and amicable numbers, and
a small class of numbers n (even when n< 1000) for which s''{n) increases
beyond the practical power of calculation [cf. Catalan^'^].

A. Gerardin^^" proved that the only pairs 2^-5a;, 2-yz of amicable num-
bers, where x, y, z are odd primes, are Euler's (a), (^3) ; the only pairs 2*-23x,
2^yz are Euler's (17), (19), (20). He cited the Exercices d'arithm^tique of
Fitz-Patrick and Chevrel; also Dupuis' Table de logarithmes, which gives
24 pairs of amicable numbers.

G^rardin^^^ proved that the only pair Sxy, S2z is Euler's (60). He made
an incomplete examination of 16-53a;, IQyz, but found no new pairs.

3"Archiv Math. Phys., 70, 1884, 75-89.

"*Bull. Soc. Math. France, 16, 1887-8, 129. Mathesis, 8, 1888, 130.

'"76id., 17, 1888-9, 155-6.

"•Lucas, Theorie dcs nombres, 1, 1891, 381.

"'Casopis mat. a fys., Praze (Prag), 25, 1896, 129-142, 209-221.

"8/6id., 349-350.

"«Proc. London Math. Soc, 35, 1902-3, 40.

""Matheshs, 6, 1906, 41^4.

"'Sphinx-Oedipe, Nancy, 1906-7, 14-15, 53.

Chap. I] PERFECT, MULTIPLY PERFECT, AND AmICABLE NUMBERS. 49

G^rardin^^^ proved that the three numbers (1) with n = m-f 2 are not all
primes if 34< m^ 60, the cases m = 38 and 53 not being decided. Replacing
m by m+1 and A; by 2^+1 in case (li) of Euler^^'*, we get the pair 2"pg,
2"r, where n = m+2g-]-2,

p = 2"*+2''+^P-l, 5 = 2"*+^P-l, ^ = 22'"+2''+3p2_i^

with P = 2^^'*"^ + l. For 9^ = 0, we have the case (1) just mentioned; all
values m^200 are excluded except m = 38, 74, 98, 146, 149, 182, 185, 197.
The case gr= 1 is excluded since i/ or 2 is a difference of two squares. For
g = 2, all values m ^ 60 are excluded except m= 29, 34, 37, 49. For g = 3, all
values <100 are excluded except m = 8, 15, 23, 92.

0. Meissner,^^^ using the notation of Cunningham,^^^ noted that n and
s{n) are amicable if s^(n)=n and raised the question of the existence of
numbers n for which s''{n)—n for k^S, so that n, s{n),. . .,s*~^(n) would
give amicable numbers of higher order. He asked if the repetition of the
operation s, a finite number (k) of times always leads to a prime, a perfect
or amicable number; also if k increases with n to infinity. On these ques-
tions, see Dickson^^^ and Poulet.^^^

A. Gerardin^^^ stated that the only values n<200 for which the
numbers (1) are all primes are the three known to Descartes.

L. E. Dickson^^^ obtained the two new pairs of amicable numbers

2*-12959-50231, 2*- 17- 137-262079; 2*- 10103-735263, 2^-17-137-2990783,

by treating the type IQpq, 16-17-137r, where p, q, r are distinct odd primes.
These are amicable if and only if

p = m+9935, g = w+9935, r = 4(w+n) +88799, wn = 2^3*7-23-73.

Although Euler^^ mentioned this type (33) in §95, he made no discussion
of it since r always exceeds the limit 100000 of the table of primes accessible
to him. An examination of the 120 distinct cases led only to the above
two amicable pairs.

Dickson^^® proved that there exist only five pairs of amicable numbers
in which the smaller number is <6233, viz., (1), (a), (^), (60) in Euler's^^*
table, and Paganini's^^^ pair. In the notation of Cunningham,^^^ the chain
n, s{n), s^{n), . . .is said to be of period k if s^(n) =n. The empirical theorem
of Catalan'^* is stated in the corrected form that every non-periodic
chain contains a prime and verified for a wide range of values of n. In
particular, if n<6233, there is no chain of period 3, 4, 5, or 6. For k odd
and > 1, there is no chain arii, an2, . . . , aUk of period k in which /ii, . . . , n^
have no common factor and each rij is prime to a> 1.

'^^Sphinx-Oedipe, 1907-8, 49-56, 65-71 ; some details are inaccurate, but the results correct.
'S'Archiv Math. Phys., (3), 12, 1907, 199; Math.-Naturw. Blatter, 4, 1907, 86 (for k=3).
'** Assoc, frang. avanc. sc, 37, 1908, 36-48; I'intenn^diaire des math., 1909, 104.
'8*Amer. Math. Monthly, 18, 1911, 109.
"•Quart. Jour. Math., 44, 1913, 264-296.

50 History of the Theory of Numbers. [Chap, i

P. Poulet'^' discovered the chain of period five,

71 = 12496 = 24-11.71, s(n)= 2^- 1947, s\n) = 2^-967, s\n) =2^-23-79,

sHn) =2^.1783,

with s^{n) =n; and noted that 14316 leads a chain of 28 terms.
Generalizations of Amicable Numbers.

Daniel Schwenter^^ noted in 1636 that 27 and 35 have the same sum of
ahquot parts. Kraft^^^ noted in 1749 that this is true of the pairs 45, 3-29;
39, 55; 93, 145; and 45, 13-19. In 1823, Thomas Taylor^^^ called two such
numbers imperfectly amicable, citing the pairs 27, 35; 39, 55; 65, 77; 51,
91; 95, 119; 69, 133; 115, 187; 87, 247. George Peacock^°o used the same
term.

E. B. Escott^"^ asked if there exist three or more numbers such that each
equals the sum of the [aliquot] divisors of the others.

A. G^rardin^°^ called numbers with the same sum of aliquot parts
nombres associes, citing 6 and 25; 5-19, 7-17, and 11-13, and many more sets.
An equivalent definition is that the n numbers be such that the product of
n — 1 by the sum of the aliquot divisors of any one of them shall equal the
sum of the aliquot divisors of the remaining n — 1 numbers.

L. E. Dickson^°^ defined an amicable triple to be three numbers such
that the sum of the aliquot divisors of each equals the sum of the remaining
two numbers. After developing a theory analogous to that by Euler^®* for
amicable numbers, Dickson obtained eight sets of amicable triples in which
two of the numbers are equal, and two triples of distinct numbers:

293-3370, 5- 16561a, 99371o (a = 25.3-13),

3-896, 11-296, 3596 (6 = 2i*.5-19-31-151).

^L'intermddiaire des math., 25. 1918, lOO-l.
♦""Encyclopaedia Metropolitana, London, I, 1845, 422.
«"L'interm6diaire des math., 6, 1899, 152.
♦""Sphinx-Oedipe, 1907-8, 81-83.
♦MAmer. Math. Monthly, 20, 1913, 84-92.

CHAPTER II.

FORMULAS FOR THE NUMBER AND SUM OF DIVISORS. PROBLEMS OF

FERMAT AND WALLIS.

Formula for the Number of the Divisors of a Number.

Cardan^ stated that a product P oi k distinct primes has 1+2+2^+ . .
-\-2^~'^ aUquot parts (divisors <P).

Michael StifeP proved this rule and found^ the number of divisors of
2*3^52p, where P = 7-11.13-17-19-23-29, by first noting that there are
1+2+ . . .+64 divisors <P oi P according to Cardan's rule and hence
128 divisors of P. The factor 5^ gives rise to 128+128 more divisors, so
that we now have 384 divisors. The factor 3^ gives 3.384 more, so that we
have 1536. Then the factor 2* gives 4.1536 more.

Mersenne* asked what number has 60 divisors; since 60 = 2-2-3-5, sub-
tract unity from each prime factor and use the remainders 1, 1, 2, 4 as
exponents; thus 3^-2*-7-5 = 5040 (so much lauded by Plato) has 60 divisors.
It is no more difficult if a large number of aliquot parts is desired.

I. Newton^ found all the divisors of 60 by dividing it by 2, the quotient
30 by 2, and the new quotient 15 by 3. Thus the prime divisors are 1, 2, 2,
3, 5. Their products by twos give 4, 6, 10, 15. The products by threes
give 12, 20, 30. The product of all is 60. The commentator J. Castillionei,
of the 1761 edition, noted that the process proves that the number of all
divisors of a'"6'*. . .is (m+l)(n+l) . . .if a, 6, . . .are distinct primes.

Frans van Schooten^ devoted pp. 373-6 to proving that a product of k
distinct primes has 2'''— 1 aliquot parts and made a long problem (p. 379)
of that to find the number of divisors of a given number. To find (pp.
380-4) the numbers having 15 aliquot parts, he factored 15+1 in all ways
and subtracted unity from each factor, obtaining abed, a^bc, a%^, a^b, a^^.
By comparing the arithmetically least numbers of these various types, he
found (pp. 387-9) the least number having 15 aliquot parts.

John Kersey'^ cited the long rule of van Schooten to find the number of
aliquot parts of a number and then gave the simple rule that Oi" . . . a^" has
(6i+l) . . . (e„+l) divisors in all if ai, . . . , a„ are distinct primes.

John Wallis^ gave the last rule. To find a number with a prescribed
number of divisors, factor the latter number in all possible ways; if the

iPractica Arith. & Mensurandi, Milan, 1537; Opera, IV, 1663.

*Arithmetica Integra, Norimbergae, 1544, lib. 1, fol. 101.

'Stifel's posthumous manuscript, fol. 12, preceding the printed text of Arith. Integra; cf. E.
Hoppe, Mitt. Math. Gesell. Hamburg, 3, 1900, 413.

*Cogitata Physico Math., II, Hydravhca Pnevmatica, Preface, No. 14, Paris, 1644. (Quoted
by Winsheim, Novi Comm. Ac. Petrop., II, ad annum 1749, Mem., 68-99). Also letter
from Mersenne to Torricello, June 24, 1644, Bull. Bibl. Storia Sc. Mat., 8, 1875, 414-5.

•Arithmetica UniversaUs, ed. 1732, p. 37; ed. 1761, I, p. 61. De Inventione Divisorum.

•Exercitationum Math., Lugd. Batav., 1657.

^The Elements of Algebra, London, vol. 1, 1673, p. 199.

•A Treatise of Algebra, London, 1685, additional treatise, Ch. III.

61

52 History of the Theory of Numbers. [Chap, ii

factors are r, s, . . ., the required number is p''~^q'~^ . . ., where p, q,. . are
any distinct primes. WTien the number of divisors is odd, the number
itself is a square, and conversely. The number of ways A^ = a^b^ . . . can be
expressed as a product of two factors is A = |(a+l)(j3+l) . . .or \-\-k,
according as N is not or is a square.

Jean Prestet^ noted that a product of k distinct primes has 2'' divisors,
while the ?ith power of a prime has n+1 divisors. The divisors of a^h^c^
are the 12 divisors of or}?, their products by c and by c^, the general rule
not being stated explicitly.

Pierre R^mond de Montmort^° stated in words that the number of
divisors of Oi**. . .a„*" is (ci+l) . . .(e„+l) if the a's are distinct primes.

Abb^ Deidier^^ noted that a product of k distinct primes has

^+^+(2) + (3)+ •

divisors, treating the problem as one on combinations (but did not sum the
series and find 2*"). To find the number of divisors of 2*3^5^ he noted that
five are powers of 2 (including unity). Since there are three divisors of 3^,
multiply 5 by 3 and add 5, obtaining 20. In view of the two divisors of
5^, multiply 20 by 2 and add 20. The answer is 60.

E. Waring^- proved that the number of divisors of a"'?)". . .is (m+1)
(n+1) . . .if a, 6, . . are distinct primes, and that the number is a square if
the number of its divisors is odd.

E. Lionnet^^ proved that if a, b, c, . . .are relatively prime in pairs, the
number of divisors of abc. . .equals the product of the number of divisors
of a by the number for b, etc. According as a number is a square or not,
the number of its divisors is odd or even.

T. L. Pujo^^ noted the property last mentioned.

Emil Hain^^ derived the last theorem from a"* = (<i . . . t„y, where <i, . . . , <„
denote the divisors of a.

A. P. Minin^^ determined the smallest integer with a given number of
divisors.

G. Fontene'" noted that, if 2"3^. . .mV (a^/S^ . . . ^n^v) is the least
number with a given number of di\4sors, then I'+l is a prime, and /x+1 is
a prime except for the least number 2^3 ha\'ing eight di\'isors.

Formula for the Sum of the Divisors of a Number. '

R. Descartes,^^ in a manuscript, doubtless of date 1638, noted that, if p
is a prim6, the sum of the aliquot parts of p" is (p"— l)/(p — 1). If 6 is the

"Nouv. Elemens des Math., Paris, 1689, vol. 1, p. 149.

loEssay d'analyse sur les jeux de hazard, ed. 2, Paris, 1713, p. 55. Not in ed. 1, 1708.
"Suite de I'arithm^tique des g^om^tres, Paris, 1739, p. 311.
i^Medit. Algebr., 1770, 200; ed. 3, 1782, 341.
"Nouv. Ann. Math., (2), 7, 1868, 68-72.
"Les Mondes, 27, 1872, 653-4.
"Archiv Math. Phys., 55, 1873, 290-3.
"Math. Soc. Moscow (in Russian), 11, 1883-4, 632.
"Nouv. Ann. Math., (4), 2, 1902, 288; proof by Chalde, 3, 1903, 471-3.
*'"De partibus ahquotis numerorum," Opuscula Posthuma Phys. et Math., Amstelodami,
1701, p. 5; Oeuvres de Descartes (ed. Tannery and Adams, 1897-1909), vol. 10, pp. 300-2.

23
3

13

Chap. II] FORMULAS FOR NUMBER AND SUM OF DiVISORS. 53

sum of the aliquot parts of a, the sum of the ahquot parts of ap is 6p+a+6.
If b is the sum of the ahquot parts of a and if x is prime to a, the sum of the
aUquot parts of ax"" is

— ^n — [=^'+^K-j^)-^^\'

Descartes^^ stated a result which may be expressed by the formula

(1) <j{nm)=(T{n)(T{m) (n, m relatively prime),

where (T{n) is the sum of the divisors (including 1 and n) of w. Here he
solved n : (T(n) = 5 : 13. Thus n must be divisible by 5. Enter 5
in column A and (r(5) = 6 in column B. Then enter the factor A B
2 in column A and (r(2) =3 in column B. Having two threes
in column B, we enter 9 in column A and cr(9) = 13 in B. Every 5
number except 13 in column B is in column A. Hence the 2
product 5-2-9 = 90 is a solution n. Next, to solve n : a- (n) = 5 : 14, 9
we enter also 13 in column A and 14 in B, and obtain the solu-
tion 90-13. If ?i is a perfect number, 5n: (7(5n) = 5: 12 and, if n?^6, 15n:
(r(15n) = 5:16.

Descartes^^ stated that he possessed a general rule [illustrated above]
for finding numbers having any given ratio to the sum of their aliquot parts.

Fermat^^ had treated the same problem. Replying to Mersenne's
remark that the sum of the aliquot parts of 360 bears to 360 the ratio 9 to 4,
Fermat^^ noted that 2016 has the same property.

John Wallis^^ noted that Frenicle knew formula (1).

Wallis^^ knew the formula

(2) ^(a•6^...) = 211^1-*^^....

a— 1 0—1

Thus these formulae were known before 1685, the date set by Peano,^^ who
attributed them to Wallis.^^

G. W. Kraft^^ noted that the method of Newton^ shows that the sum of
the divisors of a product of distinct primes P, . . ., S is (P+1) . . .(S+1).
He gave formula (1) and also (2), a formula which Cantor^" stated had
probably not earlier been in print. To find a number the sum of whose
divisors is a square, Kraft took PA, where P is a prime not dividing A.
If (r(A)=a, then (r(PA) = (P-f-l)a will be the square of (P+l)5 if P =

^^"De la fagon de trouver le nombres de parties aliquotes in ratione data," manuscript Fonds-
frangais, nouv. acquisitions, No. 3280, ff. 156-7, Bibliothfeque Nationale, Paris. Pub'
Ushed by C. Henry, BuU. Bibl. Storia Sc. Mat. e Fis., 12, 1879, 713-5.

^Oeuvres, 2, p. 149, letter to Mersenne, May 27, 1638.

K)euvre8 de Fermat, 2, top of p. 73, letter to Roberval, Sept. 22, 1636.

"Oeuvres, 2, 179, letter to Mersenne, Feb. 20, 1639.

''^ommercium Epistolicum, letter 32, April 13, 1658; French transl. in Oeuvres de Fermat, 3,
553.

"Commercium Epist., letter 23, March, 1658; Oeuvres de Fermat, 3, 515-7.

"Formulaire Math., 3, Turin, 1901, 100-1.

"Novi Comm. Ac. Petrop., 2, 1751, ad annum 1749, 100-109.

"Geschichte Math., 3, 595; ed. 2, 616.

54 History of the Theory of Numbers. [ChapII

a/S^ — 1; for A = 14, take B = 2, whence P = 5. Again, the sum of the
aUquot parts of 3P~ is (2+-P)^. The numbers AP and BPQ have the same
sum of divisors if a(P+l) = 6(P+1)(Q+1), i. e., if Q = a/6-l; takmg
a = 24, 6 = 6, we have Q = 3, a prime, .4 = 14, B = 5 (by his table of the sum
of the divisors of 1,. . ., 150); this problem had been solved otherwise by
Wolff."

L. Euler^^ gave a table of the prime factors of o-(p), a(p^), and <t(p^) for
each prime p<1000; also those of aip") for various a's for p^23 (for
instance, a ^36 when p = 2). He proved formulas (1) and (2) here and in
his^ posthumous tract, where he noted (p. 514) all the cases in which
a{n) =a-(?70 = 60.

E. Waring^2 proved formula (2). He^ noted that if P = arir. . .and
Q = a'^h^ . . . , where m — a,n — ^,... are large, then a{PQ)/a{P) is just greater
than Q. If A = {1-1)\, <t{IA)/(t{A)^1-^1. If a'br..=A and (x+l)
(2/+ 1) . . . is a maximum, then a'"''"^ = 6""^^ = . . . For a, 6, . . . distinct primes,
a{A) is not a maximum. He cited numbers with equal sums of divisors:
6 and 11, 10 and 17, 14 and 15 and 23.

L. Kronecker^^ derived the formulas for the number and sum of the
divisors of an integer by use of infinite series and products.

E. B. Escott^^ listed integers whose sum of divisors is a square.

Problems of Fer\la.t and Wallis on Sums of Divisors.

Fermat'*^ proposed January 3, 1657, the two problems: (i) Find a cube
which when increased by the sum of its aUquot parts becomes a square;*
for example, 7^ + ( 1 + 7 + 7^) = 20^. (ii) Find a square which when increased
by the sum of its aliquot parts becomes a cube.

John WalUs^^ replied that unity is a solution of both problems and pro-
posed the new problem: (m) Find two squares, other than 16 and 25, such
that if each is increased by the sum of its ahquot parts the resulting sums
are equal.

Brouncker*^ gave 1/n^ and 343/n^ as solutions (!) of problem (i).

"Elementa Analyseos, Cap. 2, prob. 87.

«Opuscula varii argumenti, 2, Berlin, 1750, p. 23; Comm. Arith., 1, 102 (p. 147 for table to 100).

Opera postuma, I, 1862, 95-100. F. Rudio, Bibl. Math., (3), 14, 1915, 351, stated that

there are fully 15 errors.
"Comm. Arith., 2, 512, 629. Opera postuma, I, 12-13.
«Meditationea Algebr., ed. 3, 1782, 343. (Not in ed. of 1770.)
"Vorlesungen iiber Zahlentheorie, I, 1901, 265-6.
^Amer. Math. Monthly, 23, 1916, 394.

*Erroneou8ly given as "cube" in the French tr., Oeuvres de Fermat, 3, 311.
'"OeuvTes, 2, 332, "premier d6fi aux mathdmaticiens;" also, pp. 341-2, Fermat to Digby, June

6, 1657, where 7' is said to be not the only solution. These two problems by Fermat

were quoted in a letter by the Astronomer Jean H6v4hus, Nov. 1, 1657, pubhshed by C.

Henry, Bull. Bibl. Storia Sc. Mat. e Fis., 12, 1879, 683-5, along with extracts from the

Commercium EpistoUcum. Cf. G. Wertheim, Abh. Geschichte Math., 9, 1899, 558-561,

570-2 ( = Zeitschr. Math. Phys., 44, Suppl. 14).
"Commercium Epistohcum de Wallis, Oxford, 1658; Walhs, Opera, 2, 1693. Letter II, from

WaUis to Brouncker, Mar. 17, 1657; letter XVI, Walhs to Digby, Dec. 1, 1657. Oeuvres

de Fermat, 3, 404, 414, 427, 482-3, 503-4, 513-5.
**Commercium, letter IX, Wallis to Digby; Fermat'e Oeuvres, 3, 419.

Chap. II] PkOBLEMS ON SUMS OF DiVISORS. 55

Frenicle^^ expressed his astonishment that experienced mathematicians
should not hesitate to present, for the third time, unity as a solution.

Wains'*^ tabulated <r{x^) for each prime a:<100 and for low powers of
2, 3, 5, and then excluded those primes a: for which (T(rc^)has a prime factor
not occurring elsewhere in the table. By similar eliminations and successive
trials, he was led to the solutions^^ of (i) :

a=3^5-lM3-41-47, 6=2-3-5-13-41-47; 7a, 7b,

adding that they are identical with the four numbers given by Frenicle.*''
Note that o-(a) is the square of 2^3^5-7-lM3-17-29-61, while a{b) is the square
of 2^3V7-13-17-29. Wallis^^ gave the further solutions of a{x^) = y^:

a:=17-3147-191, ?/=2^°325-13-17-29-37,

2-3-5-13-17.314M91, 2^^33527. i3.;^7.29237^

3'5-lM3-17-31-4M91, 2'23^5-7-lM3-17-29237-61,

and the products of each x by 7.

Wallis^^ gave solutions of his problem (m) :

2^3.37, 2-19-29; 223-1M9-37, 2'7-29.67;

29-67, 2-3-5-37; 2^7.29.67, 3-5-1M9-37.

Frenicle*^ gave 48 solutions of WalUs' problem (m), including 2-163
11-37; 3-11-19, 7-107; 2-5-151, 3^-67; also 83 sets of three squares having the
same sum of divisors, for example, the squares of

2^11.37-151, 3^67-163, 5-11-37-151, (7 = 3^7^19-31-67-1093;

also various such sets of n squares (with prime factors <500) for n^l9,
for example, the squares of ac, ad, 4:bd, 46c, 5bd, and 56c, where

a = 2-5-29-47-67-139, 6 = 13-37-191-359, c = 7.107, d = 3-ll-19.

Frans van Schooten^" made ineffective attempts to solve problems
(i), (n).

Frenicle^^ gave the solution

a: = 225-7.11-37-67-163-191-263-439-499, t/ = 327^3- 19-31^67- 109

of problem (n), a{x^)=y^; also a new solution of a{x^)=y^:
a; = 255-7-31-73-241-243-467, i/ = 2i23253ii. 13217.37.41. 113.193.257.

^'Letter XXII, to Digby, Feb. 3, 1658. Cf. Leibnitii et BernouUii Commercium philos. et

math., I, 1795, 263, letter from Johann Bernoulli to Leibniz, Apr. 3, 1697.
"Letter XXIII, to Digby, Mar. 14, 1658.
"The same tentative process for finding this solution a was given by E.Waring, Meditationes

Algebraicae, 1770, pp. 216-7; ed. 3, 1782, 377-8. The solution 6 = 751530 was quoted

by Lucas, Thiorie des nombres, 1891, 380, ex. 3.
**Solutio duorum problematum circa numeros cubos . . . 1657, dedicated to Digby [lost work].

See Oeuvres de Fermat, p. 2. 434, Note; WaUis."
"Letter XXVIII, March 25, 1658; WaUis, Opera, 2, 814; Wallia".
««Letter XXIX, Mar. 29, 1658; WaUis^^.
"Letter XXXI, Apr. 11, 1658.
"Letter XXXIII, Feb. 17, 1657 and Mar. 18, 1658.
"Letter XLIII, May 2, 1658.

56 History of the Theory of Numbers. [Chap, ii

Wallis^'^ for use in problem (ii) gave a table showing the sum of the
divisors of the square of each number < 500. Excluding numbers in whose
divisor sum occurs a prime entering the table only once or twice, there are
left the squares of 2, 4, 8, 3, 5, 7, 11, 19, 29, 37, 67, 107, 163, 191, 263, 439, 499.
By a very long process of exclusion he found only two solutions within the
limits of the table, viz., Frenicle's" and

(rj(7.11-29.163-191439)2[ = ]3.7-13-19-31-67(^

Jacques Ozanam" stated that Fermat had proposed the problem to find
a square which with its aliquot parts makes a square (giving 81 as the answer)
and the problem to find a square whose aliquot parts make a square. For
the latter, Ozanam found 9 and 2401, whose aliquot parts make 4 and
400, and remarked that he did not believe that Fermat ever solved these
questions, although he proposed them as if he knew how.

Ozanam^ noted that the sum of 961 = 31^ and its aliquot parts 1 and 31
is 993, which equals the sum of the aliquot parts of 1 156 = 34". As examples
of two squares with equal total sums of divisors [WaUis' problem (m)], he
cited 16 and 25, 326^ and 407^, while others may be derived by multiplying
these by an odd square not divisible by 5. The sum of all the divisors of
9^ is 11^ that of 20^ is 31l The numbers 99 and 63 have the property that
the sum 57 of the aliquot parts of 99 exceeds the sum 41 of the aliquot
parts of 63 by the square 16; similarly for 325 and 175.

E. Lucas^^ noted that the problem to find all integral solutions of

(1) l-\-x+z^-\-x^ = y^
is equivalent to the solution of the system

(2) l+x = 2w2, l+x2 = 2t;2, y = 2uv,

and stated that the complete solution is given by that of 2y^— x^ = l.
E. Gerono^^ proved that the only solutions of (1) are

(x, 2/) = (-l, 0), (0, ±1), (1, ±2), (7, ±20).

E. Lucas^^ stated that there is an infinitude of solutions of Fermat's
problem (i); the least composite solution is the cube of 2-3-5-13'41-47, the
sum of whose divisors is the square of 2^3^5^7- 13- 17-29. [This solution was
given by Frenicle.^®] For the case of a prime, the problem becomes (1).

A. S. Bang^^ gave for problem (i) the first of the three answers by Wallis;*'
for (it), (7(43098^) = 1729^ for {in), 29-67, 2-3-5-37 of Wallis^* and the first
two by Frenicle;^^ all without references.

"A Treatise of Algebra, 1685, additional treatises, Ch. IV.

"Letter to De Billy, Nov. 1, 1677, published by C. Henry, Bull. Bibl. Storia Sc. Mat. e Fia., 12,

1879, 519. Reprinted in Oeuvres de Fermat, 4, 1912, p. 140.
"Recreations Math6matiques et Phys., new ed., 1723, 1724, 1735, etc., Paris, I, 41-43.
"Nouv. Corresp. Math., 2, 1876, 87-8.
••Nouv. Ann. Math., (2), 16, 1877, 230-4.
"Bull. Bibl. Storia Sc. Mat. e Fis., 10, 1877, 287.
"Nyt Tidsskrift for Mat., 1878, 107-8; on problems in 1877, 180.

Chap. II] PROBLEMS ON SUMS OF DiVISORS. 57

E. Fauquembergue,^^ after remarking that (1) is equivalent to the sys-
tem (2), cited Fermat's^" assertion that the first two equations (2) hold
only for a: = 7 [aside from the evident solutions a: = ± 1, 0], which has been
proved by Genocchi.^^

H. Brocard^^ thought that Fermat's assertion that 7^ is not the only
solution of problem (i) implied a contradiction with Genocchi.^^ G. Vacca
{ihid., p. 384) noted the absence of contradiction as (i) leads to equation (1)
only if a: be a prime.

C. Moreau®^ treated the equation, of type (1),

While he used the language of extracting the square root of X = x*+ . . .
written to the base x, he in effect put X={x^-\-a)^, 0<a<x. Then a^ =
x+1, 2ax^ = x^-\-x^, whence 2a = a^, a = 2, x = 3, y = ll.

E. Lucas®^ stated that {x^-\-y^)/{x+y) =^ has the solutions

(3,-1, 11), (8, 11, 101), (123, 35, 13361),. . .

Moret-Blanc^^ gave also the solutions (0, 1, 1), (1, 1, 1).
E. Landau^^ proved that the equation

— T=y^

x — 1
is impossible in integers (aside from x = 0, ?/ = =fc 1) for an infinitude of values
of n, viz., for all n's divisible by 3 such that the odd prime factors of n/3, if
any, are all of the form 6y— 1 (the least such n being 6). For, setting
n = 3m, we see that y^ is the product of x^+x+1 and F = x^"'~^-{- . . . +a:^+l.
These two factors are relatively prime since x^=l gives F=m (mod x^+
a: + 1 ) . Hence x^+x+lis Si square, which is impossible for a; f^ 0 since it lies
between x^ and (a:+l)^.

Brocard^^ had noted the solution a: = 1, y=m, if n = mP.

A. Gerardin^^ obtained six new solutions of problem (i) :

a: = 2.47.193.239.701, 2/ = 2^3l5M3M7.97.149.

x = 2.5.23.41.83.239, y = 2\S\5\7.1S\29.53.

x = 3.13.23.47.83.239, y = 2^^3^517.13117.53.

X = 2.3.13.23.83.193.701, y = 2^3^5^7.13.17.53.97.149.

a; = 3.5.13.41.193.239.701, 2/ = 2^3l5l7.13M7.29.97.149.

a; = 2.5.13.43.191.239.307, ?/ = 2i^32.5MlM7.29.37.53.113.197.241.257.

Also <t{N^)=S^ for Ar = 3-7-ll-29-37, ^ = 3-7-13-19-67.

"Nouv. Ann. Math., (3), 3, 1884, 538-9.

'"Oeuvres, 2, 434, letter to Carcavi, Aug., 1659.

"Nouv. Ann. Math., (3), 2, 1883, 30&-10. Cf. Chapter on Diophantine Equations of order 2.

"L'intermMiaire des math., 7, 1900, 31, 84.

"Nouv. Ann. Math., (2), 14, 1875, 335.

»Ibid., 509.

«76id., (2), 20, 1881, 150.

"L'interm^diaire des math., 8, 1901, 149-150.

"Ibid., 22, 1915, 111-4, 127.

58 History of the Theory of Numbers. [Chap.ii

G^rardin^^ gave five new solutions of (i) :

X = 3.11.31.443.499, i/ = 2^3.5M3.37.61.157.

x = 2.3^31.443.449, 2/ = 2^3.5ni. 13.37.61.157.

a; = 1 1 . 17.41 .43.239.307.443.499,

2/ = 2^2 3^5'.7.11. 13^29^.37.61. 157.
x = 2.11. 17.23.41.211.467.577.853,

t/ = 2^''.3^5l7.13M7.292.53.61. 113.193.197.
x = 3ni. 13.23.83.193.701,

?/ = 293'537.11. 13.17.53.61.97.149,
the last following from his*^^ fourth pair in \'iew of

a{SnV): a{2'S') = 2'3.nm^: 233.52 = 2=11-612; 5=.

A. Cunningham and J. Blaikie^^ found solutions of the form x = 2'p of
s{x) =g^, where s{n) is the sura of the divisors <n of n.

product of aliquot parts.

Paul Halcke'^^ noted that the product of the aliquot parts of 12, 20, or
45 is the square of the number; the product for 24 or 40 is the cube; the
product for 48, 80 or 405 is the biquadrate.

E. Lionnet"^ defined a perfect number of the second kind to be a number
equal to the product of its aliquot parts. The only ones are p^ and pq,
where p and q are distinct primes.

"L'interm^diaire des math., 24, 1917, 132-3.

"Math. Quest. Educ. Times, (2), 7, 1905, 68-9.

"Dehciae Math, oder Math. Sinnen-Confect, Hamburg, 1719, 197, Exs. 150-2.

"Nouv. Ann. Math., (2), 18, 1879, 306-8. Lucas, Th6orie des nombres, 1891, 373, Ex. 6

I

CHAPTER III.

FERMAT'S AND WILSON'S THEOREMS, GENERALIZATIONS AND

CONVERSES; SYMMETRIC FUNCTIONS OF

1,2 P-\ MODULO P.

Fermat's and Wilson's Theorems; Immediate Generalizations.

The Chinese^ seem to have known as early as 500 B. C. that 2^—2 is
divisible by the prime p. This fact was rediscovered by P. de Fermat^
while investigating perfect numbers. Shortly afterwards, Fermat^ stated
that he had a proof of the more general fact now known as Fermat's theorem:
If p is any prime and x is any integer not divisible by p, then x^~^ — 1 is
divisible by p.

G. W. Leibniz^ (1646-1716) left a manuscript giving a proof of Fermat's
theorem. Let p be a prime and set x = a+6+c+. . .. Then each multi-
nominal coefficient appearing in the expansion of x^ — 2a^ is divisible by p.
Take a = 6 = c=...=l. Thus a;^ — a: is divisible by p for every integer x.

G. Vacca^ called attention to this proof by Leibniz.

Vacca^ cited manuscripts of Leibniz in the Hannover Library showing
that he proved Fermat's theorem before 1683 and that he knew the theorem
now known as Wilson's^^ theorem: If p is a prime, l + (p — 1)! is divisible
by p. But Vacca did not explain an apparent obscurity in Leibniz's state-
ment [cf. Mahnke'^].

D. Mahnke'' gave an extensive account of those results in the manuscripts
of Leibniz in the Hannover Library which relate to Fermat's and Wilson's
theorems. As early as January 1676 (p. 41) Leibniz concluded, from the
expressions for the ^th triangular and yth. pyramidal numbers, that

(2/+l)2/=2/'-2/=0 (mod 2), {y+2){y+l)y=y'-y=0 (mod 3),

and similarly for moduU 5 and 7, whereas the corresponding formula for
modulus 9 fails for y = 2, — thus forestalling the general formula by Lagrange.^*
On September 12, 1680 (p. 49), Leibniz gave the formula now known as
Newton's formula for the sum of like powers and noted (by incomplete
induction) that all the coefficients except the first are divisible by the
exponent p, when p is a prime, so that

a''+h''+c''-{- . . . = {a+h+c+ . . .Y (mod p).

Taking a = b= . . . =1, we obtain Fermat's theorem as above.'* That the
binomial coefficients in (1 + 1)^ — 1 — 1 are divisible by the prime p was

^G. Peano, Formulaire math., 3, Turin, 1901, p. 96. Jeans.^^"

''Oeuvres de Fermat, Paris, 2, 1894, p. 198, 2°, letter to Mersenne, June (?), 1640; also p. 203,

2; p. 209.
"Oeuvres, 2, 209, letter to Frenicle de Bessy, Oct. 18, 1640; Opera Math., Tolosae, 1679, 163.
*Leibnizens Math. Schriften, herausgegeben von G. J. Gerhardt, VII, 1863, 180-1, "nova

algebrae promotio."
»Bibliotheca math., (2), 8, 1894, 46-8.
•Bolletino di BibUografia Storia Sc. Mat., 2, 1899, 113-6.
'Bibliotheca math., (3), 13, 1912-3, 29-61.

69

60 History of the Theory of Numbers. [Chap, hi

proved in 1681 (p. 50). Mahnke gave reasons (pp. 54-7) for believing
that Leibniz rediscovered independently Fermat's theorem before he
became acquainted, about 1681-2, with Fermat's Varia opera math, of
1679. In 1682 (p. 42), Leibniz stated that (p-2)!=l (mod p) if p is a
prime [equivalent to Wilson's theorem], but that {p—2)l=m (mod p), if
p is composite, m ha\dng a factor > 1 in common wdth p.

De la Hire^ stated that if k-'"^^ is divided by 2(2r+l) we get A; as a
remainder, perhaps after adding a multiple of the divisor. For example,
if kr' is divided by 10 we get the remainder k. He remarked that Carr^
had observed that the cube of any number /:<6 has the remainder k when
divided by 6.

L. Euler^ stated Fermat's theorem in the form: If n+1 is a prime divid-
ing neither a nor h, then a" — 6" is divisible by n+1. He was not able to
give a proof at that time. He stated the generaUzation : If e = p'"~Hp — 1)
and if p is a prime, the remainder obtained on dividing a* by p"" is 0 or 1
[a special case of Euler^^]. He stated also that ii m, n, p,. . . are distinct
primes not dividing a and if A is the 1. c. m. of m — 1, n — 1, p — 1, . . ., then
o"* — 1 is divisible by mnp . . . [and a* — 1 by m'' n\ . .ii k = A rrC~^n^~^ . . .].

Euler^° first published a proof of Fermat's theorem. For a prime p,

2'' = (l + l)^ = l+p-h(^)H-...+p+l = 2+mp,
3P = (l+2)P = l+A:p+2^ 3^-3- (2^-2) = A:p,

(1+0)"= 1+np+aP, (l+o)P-(l+a)-(aP-a)=np.

Hence if a^—a is divisible by p, also (1+a)" — (1+a) is, and hence also
(a+2)''-(a+2),. . ., (a+6)P-(a+6). For a = 2, 2" - 2 was proved divisible
by p. Hence, wTiting x for 2+6, we conclude that x^—x is divisible by p
for any integer x.

G. W. Kraft^^ proved similarly that 2" — 2 = 7np.

L. Euler's^- second proof is based, hke his first, on the binomial theorem.
If a, 6 are integers and p is a prime, (a+6)"— a" — 6" is divisible by p. Then,
if a^ — a and 6^ — 6 are di\'isible by p, also (a+6)" — a — 6 is di\4sible by p.
Take h = \. Thus (a+1)"— a— 1 is divisible by p if a^—a is. Taking
a = 1, 2, 3, ... in turn, we conclude that 2''— 2, 3"— 3, . . . , c^ — c are divisible
by p.

L. Euler^^ preferred his third proof to his earlier proofs since it avoids
the use of the binomial theorem. If* p is a prime and a is any integer not

*Hist. Acad. Sc. Paris, annee 1704, pp. 42-4; ra4m., 358-362.

»Comm. Ac. Petrop., 6, 1732-3, 106; Coram. Arith., 1, 1849, p. 2. [Opera postuma, I, 1862,

167-8 (about 1778)].
^••Comm. Ac. Petrop., 8, ad annum 1736, p. 141; Comm. Arith., 1, p. 21.
"Novi Comm. Ac. Petrop., 3, ad annos 1*50-1, 121-2.
"Novi Comm. Ac. Petrop., 1, 1747-8, 20; Comm. Arith., 1, 50. Also, letter to Goldbach,

Mar. 6, 1742, Corresp. Math. Phys. (ed. Fuss), I, 1843, 117. An extract of the letter is

given in Nouv. Ann. Math., 12, 1853, 47.
"Novi Comm. Ac. Petrop., 7, 1758-9, p. 70 (ed. 1761, p. 49); 18, 1773, p. 85; Comm. Arith., 1,

260-9, 518-9. Reproduced by Gauss, Disq. Arith., art. 49; Werke, 1, 1863, p. 40.

Chap. Ill] FerMAt's AND WiLSON's THEOREMS. 61

divisible by y, at most p — 1 of the positive residues < p, obtained by dividing
1, a, a^, . . . by p, are distinct. Let, therefore; a" and a", where ix^v, have the
same residue. Then a""" — 1 is divisible by p. Let X be the least positive
integer for which a^ — \ is divisible by p. Then \,a,a^,..., a^~^ have dis-
tinct residues when divided by p, so that X^p — L IfX = p — 1, Fermat's
theorem is proved. If X<p — 1, there exists a positive integer k ik<p)
which is not the residue of a power of a. Then k, ak, a^k, . . ., a^~^k have
distinct residues, no one the residue of a power of a. Since the two sets
give 2X distinct residues, we have 2X^ p — 1. If X< (p — 1)/2, we start with
a new residue s and see that s, as, a^s, . . ., a^~^s have distinct residues, no one
the residue of a power of a or of a^k. Hence X^ (p — 1)/3. Proceeding in
this manner, we see that X divides p — L Thus d^~^ — 1 is divisible by a'' — 1
and hence by p.

L. Euler^^ soon gave his fundamental generalization of Fermat's theorem
from the case of a prime to any integer N:

Euler's theorem: If n=(f){N) is the number of positive integers not
exceeding N and relatively prime to N, then x" — 1 is divisible by N for
every integer x relatively prime to N.

Let V be the least positive integer for which x" has the residue 1 when
divided by N. Then the residues of 1, a:, a:^, ... , x"'^ are distinct and prime
to N. Thus v^n. If v<n, there is an additional positive integer a less
than A'' and prime to N. Then, when a, ax, ax^, . . ., ax"'^ are divided by N,
the residues are distinct from each other and from those of the powers of x.
Thus, 2v^n. Similarly, if 2v<n, then Zv^n. It follows in this manner
that V divides n.

J. H. Lambert^^ gave a proof of Fermat's theorem differing shghtly from
the first proof by Euler.^" If h is not divisible by the prime p, 6^"^ — 1 is
divisible by p. For, set 6 = c+L Then

6^-^-1 =-l+c''-i + (p-l)c^-2+...+l

= -l+c^-'-c^-2 +0^"^- . . . +1+Ap,

where A is an integer. The intermediate terms equal

Hence

c+1 c+1

-fA-/, /='

P p ' P(c+1)

The theorem will thus follow by induction if / is shown to be integral.
[Take p>2, so that p — 1 is even.] Then c^"^ — 1 is divisible by c+l, and
by the hypothesis for the induction, by p. Since c-\-l = h is relatively
prime to p, / is an integer.

"Novi Comm. Ac. Petrop., 8, 1760-1, p. 74; Comm. Arith., 1, 274-286; 2, 524-6.
"Nova Acta Eruditorum, Lipsiae, 1769, 109.

62 History of the Theory of Numbers. [Chap, hi

E. Waring^^ first published the theorem that [Leibniz®] l + (p — 1)! is
divisible by the prime p, ascribing it to Sir John Wilson^^ (1741-1793).
Waring (p. 207; ed. 3, p. 356) proved that if a^ — a is divisible by p, then
(a+1)''— a — 1 is, since {a+iy = a^-\-pA-\-l, "a, property first invented by
Dom. Beaufort and first proved by Euler."

J. L. Lagrange^^ was the first to publish a proof of Wilson's theorem. Let

(x+l)(x+2) . . . (x+p-l) =x''-^+AiX^-'+ . . . -h^p-i.

R eplace x by x + 1 and multiply the resulting equation by x + 1 . Comparing
with the original equation multiplied by x+p, we get

{x+p){x^-'+. . . +A,_,) = {x+ir+Ai{x+ir-' + . . . +^p_i(x+l).

Apply the binomial theorem and equate coefl5cients of like powers of x.
Thus

Let p be a prime. Then, for 0<k<p, (j) is an integer divisible by p.
Hence Ai, 2A2, . . . , {p—2)Ap_2 are divisible by p. Also,

(P-1)4,..= (P + (PI})A:+(P-2)^+... = 1+^+A,+ ...+^,.2.

Thus 1+Ap_i is divisible by p. By the original equation, Ap_i = (p — 1)!,
so that Wilson's theorem follows.

Moreover, if x is any integer, the proof shows that

xP-^-l-(x+l)(x+2)...(x+p-l)

is divisible by the prime p. If x is not divisible by p, some one of the
integers x+1,. . .,x+p — 1 is divisible by p. Hence x''"^ — 1 is divisible by
p, giving Fermat's theorem.

Lagrange deduced Wilson's theorem from Fermat's. By the formula^*
for the differences of order p — 1 of P~\ . . ., n^~^,

(1) (p-i)\=p^-'-{p-i){p-iy-'+(^p~^){p-2r-'

-(^3^)(p-3)^-^+. . .+(-1)^-^

Dividing the second member by p, and applying Fermat's theorem, we
obtain the residue

"Meditationes algebraicae, Cambridge, 1770, 218; ed. 3, 1782, 380.

"On his biography see Nouv. Corresp. Math., 2, 187.6, 110-114; M. Cantor, Bibliotheca math.,

(3), 3, 1902, 412; 4, 1903, 91.
"Nouv. M6m. Acad. Roy. BerUn, 2, 1773, ann^e 1771, p. 125; Oeuvres, 3, 1869, 425. Cf. N.

Nielsen, Danske Vidensk. Selsk. Forh., 1915, 520.
"Euler, Novi Comm. Ac. Petrop., 5, 1754-5, p. 6; Comm. Arith., 1, p. 213; 2, p. 532; Opera

postuma, Petropoli, 1, 1862, p. 32.

Chap. Ill] FeRMAt's AND WiLSON's THEOREMS. 63

Finally, Lagrange proved the converse of Wilson's theorem: If n divides
l + (n— 1)!, then n is a prime. For n = 4m+l, w is a prime if (2-3. . .2my
has the remainder —1 when divided by n. For n = 4m — 1, if (2m — 1)! has
the remainder =±=1.

L. Euler^" also proved by induction from a: = n to n+1 that

(2) xl = a'-x{a-ir+(^iya-2r-(^f){a-Sr+...,

which reduces to (1) ior x = p — l, a = p; and more generally,

(3) a^_n{a-ir+(^){a-2y- . . . +(-l)^Q (a-A:r+ . . . =|^, ^^

x<n
x = n.

D'Alembert^^ stated that the theorem that the difference of order m of a*"
is m ! had been long known and gave a proof.

L. Euler^^ made use of a primitive root a of the prime p to prove Wilson's
theorem (though his proof of the existence of a was defective). When
l,a,a^, . . ., oF~^ are divided by p, the remainders are 1, 2, 3, . . . , p — 1 in some
order. Hence a(p-i)(p-2)/2 j^^s the same remainder as (p — 1) !. Taking p>2,
we may set p = 2n+l. Since a" has the remainder —1, then a"a^"^'*~^\ and
hence also (p — 1)!, has the remainder —1.

P. S. Laplace^^ proved Fermat's theorem essentially by the first method
of Euler^° without citing him: If a is an integer <p not divisible by the
prime p,

^l = \a-l^lY = \\{a-iy+p{a-iy-'+ . . . +l[ ,
a a a

aV-^-\=-\{a-lY-\-l-a+hp{a-V)\ =^—^\{a-iy-^-l+hp] .
a Cv

Hence by induction a^~^ — l is divisible by p. For a>p, set a = np+q and
use the theorem for q.

He gave a proof of Euler's^^ generalization by the method of powering:
if n = p''p{\ . ., where p, Pi,... are distinct primes, and if a is prime to n,
then d° — l is divisible by n, where

-"(^)(^) ■='^'

q = p''-\p-l), r = pr-\Pi-l)P2''-\p2-l).. ..

Set a'^ = x. Then a' — l=x'" — 1 is divisible by x — 1. Using the binomial
theorem and a^~^ — l = hp, we find that aj — 1 is divisible by p".

"Novi Comm. Ac. Petrop., 13, 1768, 28-30.

"Letter to Turgot, Nov. 11, 1772, in unedited papers in the Biblioth^que de I'lnstitut de
France. Cf. BuU. Bibl. Storia Sc. Mat. e Fis., 18, 1885, 531.

"Opuscula analytica, St. Petersburg, 1, 1783 [Nov. 15, 1773], p. 329; Comm. Arith., 2, p. 44;
letter to Lagrange (Oeuvres, 14, p. 235), Sept. 24, 1773; Euler's Opera postuma, I, 583.

"De la Place, Th^orie abr^g^e des nombres premiers, 1776, 16-23. His proofs of Fermat's
and Wilson's theorems were inserted at the end of Bossut's Algdbre, ed. 1776, and
reproduced by S. F. Lacroix, Trait6 du Calcul Diff. Int., Paris, ed. 2, vol. 3, 1818, 722-4,
on p. 10 of which is a proof of (2) for o=a; by the calculus of differences.

64 History of the Theory of Numbers. [Chap, ill

From the (p — l)th order of differences for x""^ — 1,

{x+p-ir-'-i-{p-i)\{x-\-p-2r-'-i\ + (^p~^y,{x-{-p-sr-'-i\

Set x = l and use Fermat's theorem. Hence l + (p — 1)! is divisible by p.

E. Waring/^ 1782, 380-2, made use of

x' = xix-l). . .{x-r-{-l)-\-Pxix-l). . .(x-r+2)

+Qxix-1) . . .(x-r+3)+ . . . +Hx(x-l)+Ix,

where P = H-2+ • • . -f (r — 1), Q = PA^—B, etc., B denoting the sum of the
products of 1, 2,..., r — 1 two at a time, and A^ = l+2+ . . . +(r— 2).
Then

r+2'+ . . .+x^ = -^{x+l)x{x-l) . . .ix-r+l)+-{x+l)x. ..{x-r+2)
r+1 r

+-^(x+l)x. ..{x-r+3)+. . . +^ix+l)x{x-l)-\-Ux+l)x.

Take r = x and let x+1 be a prime. By Fermat's theorem, V, 2"^, . . ., x'
each has the remainder unity when divided by x+1, so that their sum has
the remainder x. Thus l+x\ is divisible by x+1.

Genty^^ proved the converse of Wilson's theorem and noted that an
equivalent test for the primahty of p is that p divide (p— n)!(n — 1)! —
( - 1)". For n = (p+ 1)/2, the latter expression is \ (^zi) !^ 2± i [Lagrange^^].

Franz von Schaffgotsch^^ was led by induction to the fact (of which he
gave no proof) that, if n is a prime, the numbers 2, 3, . . . , n — 2 can be paired
so that the product of the two in any pair is of the form xn+1 and the two
of a pair are distinct. Hence, by multipUcation, 2-3...(n — 2) has the
remainder unity when divided by n, so that (n — 1)! has the remainder
n — 1. For example, if n = 19, the pairs are 2-10, 4-5, 3-13, 7-11, 6-16,
8-12, 9-17, 14-15. Similarly, for n any power of a prime p, we can so
pair the integers <n — l which are not divisible by p. But for n=15, 4
and 4 are paired, also 1 1 and 1 1 . Euler^^ had already used these associated
residues (residua sociata).

F. T. Schubert^^" proved by induction that the nth order of differences
of r, 2",....isn!.

A. M. Legendre-^ reproduced the second proof by Euler^^ of Fermat's
theorem and used the theory of differences to prove (2) for a = x. Taking
a; = p — 1 and using Fermat's theorem, we get (p — 1)!=(1 — 1)" — 1 (mod p).

"Histoire et m6m. de I'acad. roy. sc. insc. de Toulouse, 3, 1788 (read Dec. 4, 1783), p. 91.

"Abhandlungen d. Bohmischen Gesell. Wiss., Prag, 2, 1786, 134.

"Opusc. anal., 1, 1783 (1772), 64, 121; Novi Comm. Ac. Petrop., 18, 1773, 85, §26; Comm.

Arith. 1, 480, 494, 519.
""Nova Acta Acad. Petrop., 11, ad annum 1793, 1798, mem., 174-7.
"Th6orie des nombres, 1798, 181-2; ed. 2, 1808, 166-7.

Chap. Ill] FeRMAt's AND WiLSON's THEOREMS. * 65

C. F. Gauss^^ proved that, if n is a prime, 2, 3, . . . , n— 2 can be associated
in pairs such that the product of the two of a pair is of the form xn+1.
This step completes Schaffgotsch's^^ proof of Wilson's theorem.

Gauss^^ proved Fermat's theorem by the method now known to be
that used by Leibniz^ and mentioned the fact that the reputed proof by
Leibniz had not then been published.

Gauss^*^ proved that if a belongs to the exponent t modulo p, a prime,
then a-a^-a^ . . .a^^i — lY'^^ (mod p). In fact, a primitive root p of p
may be chosen so that a=p^^~^^'\ Thus the above product is congruent
to p*, where

Thus p*=(p~2~}''^^ = ( — 1)'"*"^ (mod p). When a is a primitive root, a,
a^,. . ., aF~^ are congruent to 1, 2, . . . , p — 1 in some order. Hence (p — 1) !=
( — 1)^. This method of proving Wilson's theorem is essentially that of
Euler.22

Gauss^^ stated the generalization of Wilson's theorem: The product of
the positive integers < A and prime to A is congruent modulo ^ to — 1 if
A = 4, p"* or 2p^, where p is an odd prime, but to + 1 if ^ is not of one of
these three forms. He remarked that a proof could be made by use of
associated numbers^^ with the difference that a;^=l (mod A) may now
have roots other than ± 1 ; also by use of indices and primitive roots^° of a
composite modulus.

S. F. Lacroix^^ reproduced Euler's^^ third proof of Fermat's theorem
without giving a reference.

James Ivory^^ obtained Fermat's theorem by a proof later rediscovered
by Dirichlet.^" Let N be any integer not divisible by the prime p. When
the multiples N, 2N, SN, . . ., {p — l)N are divided by p, there result p dis-
tinct positive remainders <p, so that these remainders are 1, 2, . . ., p — 1
in some order .^^ By multiplication, N^~^Q = Q-\-mp, where Q = (p — 1)!.
Hence p divides iV^~^ — 1 since it does not divide Q.

Gauss^^ used the last method in his proof of the lemma (employed in his
third proof of the quadratic reciprocity law): If k is not divisible by the
odd prime p, and if exactly /x of the least positive residues of k, 2k,. . .,
l{p-l)k modulo p exceed p/2, then k^p-'^^^^= ( - 1)" (mod p) . [Cf . Grunert.^^]

''^Disquisitiones Arith., 1801, arts. 24, 77; Werke, 1, 1863, 19, 61.

2*Disq. Arith., art. 51, footnote to art. 50.

soDisq. Arith., art. 75.

^iDisq. Arith., art. 78.

32Compl4ment des 416mens d'alglbre, Paris, ed. 3, 1804, 298-303; ed. 4, 1817, 313-7,

"New Series of the Math. Repository (ed. Th. Leybourn), vol. 1, pt. 2, 1806, 6-8.

"A fact known to Euler, Novi Comm. Acad. Petrop., 8, 1760-1, 75; Comm. Arith., 1, 275;

and to Gauss, Disq. Arith., art. 23. Cf. G. Tarry, Nouv. Ann. Math., 18, 1899,

149, 292.
^''Comm. soc. reg. so. Gottingensis, 16, 1808; Werke, 2, 1-8. Gauss' Hohere Arith., German

transl. by H. Maser, Berhn, 1889, p. 458.

66 History of the Theory of Numbers. [Chap, hi

J. A. Gninert^® considered the series

K n] = n-- (^) (71-1)-+ Q (n-2r- . . .,

to which Euler's (3) reduces for a = n, x = m, and proved that

[m, n]=n\[m — l, n — l] + [w — 1, n]\ .
This recursion formula gives

[m,n] = 0 (m = 0, l,...,n-l); [72, n]=n\ [cf. (2)],

Any [m, n] is di\isible by n\. As by the proof of Lagrange,^^ [m, n] + ( — 1)"
is di\isible by w + 1 if the latter is a prime >n. Again,

which for x = 0, h=l, gives [m, m]=ml.

W. G. Horner^" proved Euler's theorem by generaUzing Ivory's^^ method.
If ri, . . . , r^ are the integers <m and prime to m, then riN, . . . , r^N have the
r's as their residues modulo m.

P. F. Verhulst^^ gave Euler's proof^^ in a sUghtly different form.

F. T. Poselger^^ gave essentially Euler's^° first proof.

G. L. Dirichlet^° derived Fermat's and Wilson's theorems from a com-
mon source. Call m and n corresponding numbers if each is less than the
prime p and if mn=a (mod p), where a is a fixed integer not di\dsible by p
(thus generahzing Euler's-^ associated numbers). Each number 1, 2, . . .,
p — 1 has (5ne and but one corresponding number. If a:"=a (mod p) has no
integral solution, corresponding numbers are distinct and

(p-l)!=a^-^)''2 (modp).

But if A; is a positive integer <p such that ^'^=a (mod p), the second root
is p — A', and the product of the numbers 1, . . ., p — 1, other than k and p—k,
has the same residue as a^^~^^^^, whence

(p-l)!=-a^-i^/2(j^Q^p)

The case a = 1 leads to Wilson's theorem. By the latter, we have

a(p-i)/2=±i (modp),

"Math. Abhandlungen, Erste Sammlung, Altona, 1822, 67-93. Some of the results were
quoted by Gnmert, Archiv Math. Phys., 32, 1859, 115-8. For an interpretation in
factoring of [m, n], see Minetola'" of Ch. X.

"Annals of Phil. (Mag. Chem. . . .), new series, 11, 1826, 81.

>8Corresp. Math. Phys. (ed. Qu^telet), 3, 1827, 71.

"Abhand. Ak. Wiss. Berhn (Math.), 1827, 21.

"Jour, fiir Math., 3, 1828, 390; Werke, 1, 1889, 105. Dirichlet," §34.

Chap. Ill] FeRMAT's AND WiLSON's THEOREMS. 67

the sign being + or — according as A;^=a (mod p) has or has not integral
solutions (Euler's criterion). Squaring, we obtain Fermat's theorem.
Finally, Dirichlet rediscovered the proof by Ivory .^^ [Cf. Moreau.-^^^]
J. Binet^^ also rediscovered the proof by Ivory .^^
A. Cauchy^^ gave a proof analogous to that by Euler.^"
An anonymous writer^^ proved that if n is a prime the binomial coeffi-
cient (n — l)k has the residue ( — 1)*' modulo n, so that

{l+xr-'-l=-x+x^- . . .+x''-\ {l+x)\{l+xy-^-l\^x{x''-^-l),

modulo n. Thus Fermat's theorem follows by induction on x as in the
proof by Euler.^^

V. Bouniakowsky^ gave a proof of Euler's theorem similar to that by
Laplace. ^^ If a^h is divisible by a prime p, aP^-'ifo^""' is divisible by p",
provided p>2 when the sign is plus. Hence if p, p' ,. . . are distinct primes,
o'±6' is divisible by iV = p"p"*'. . . , where t = p''~^p"''~^ . . . , if a=*=6 is divisible
by pp' . . . , provided the p's are > 2 if the sign is plus. Replace a by its
(p — l)th power and 6 by 1 and use Fermat's theorem; we see that a' — l is
divisible by N if e=(f}{N). The same result gives a generalization of
Wilson's theorem^

U?)-l)!t^'*"+l=0(modp").

He gave {ibid., 563-4) Gauss'^" proof of Wilson's theorem.

J. A. Grunert^^ used the known fact that, if 0<k<p, then k, 2k,. . .,
(p — l)k are congruent to 1, 2, . . ., p — 1 in some order modulo p, a prime,
to show that kx=l (mod p) has a unique root x. Wilson's theorem then
follows as by Gauss. If {ibid., p. 1095) we square Gauss' formula,^^ we get
Fermat's theorem.

Giovanni de Paoli^® proved Fermat's and Euler's theorems. In

(x+iy=x^-\-i-{-pS,,

where p is a prime, S^ is an integer. Change x to x — 1, . . . , 2, 1 and add the
resulting equations. Thus

x-l

x^-x^p^S,.

Replace x by a:"*, divide by x"^ and set y = x^~'^. Thus

r - 1 = pXm, X^=XSz"'/x'' = integer.

Replace m by 2m,..., {p — l)m, add the resulting equations, and set

Y„=l +Xrn+X2m-\- ■ • . +X(,^i),n. Thus

r"-l=p(y"-l)F^ = p^X^7^.

"Jour, de I'^cole polytechnique, 20, 1831, 291 (read 1827). Cauchy, Comptes Rendus Paris,

12, 1841, 813, ascribed the proof to Binet.
«Exer. de math., 4, 1829, 221; Oeuvres, (2), 9, 263. R^sumg analyt., Turin, 1, 1833, 10.
«Jour. fiir Math., 6, 1830, 100-6.

"M6m. Ac. Sc. St. P^tersbourg, Sc. Math. Phys. et Nat., (6), 1, 1831, 139 (read Apr. 1, 1829).
"Kliigel's Math. Worterbuch, 5, 1831, 1076-9.
"Opuscoli Matematici e Fisici di Diversi Autori, Milano, 1, 1832, 262-272.

68 History of the Theory of Numbers. [Chap, hi

Change m to mp, . . . , T/zp""^. Thus

2/-^ - 1 = p(^-^ - 1) F^, = p^X^y^F^,,

Hence x^^^ — 1 is divisible by N for iV" = p" and so for any N.

For X odd, x^ — 1 is divisible by 8, and x*'" — 1 by 2(x^*"— 1). As above,
he found that x' - 1 is divisible by 2* for t = m-2'-^, i> 2. Thus, if iV = 2'n,
n odd, X*— 1 is divisible by N for A: = 2*"^0(n).

A. L. Crelle^^ employed a fixed quadratic non-residue v of the prime p,
and set j^=ry, vf=Vj (mod p). By multipUcation of

ip-jf=rj, vf=v^ (mod p) (i = 1, • • • »^^)

and use of v^^~'^^'^= — \, we get

-](p-l)!f2=nr,v,= (p-l)! (modp).

F. Minding^* proved the generaUzed Wilson theorem. Let P be the
product of the tt integers a, /3, . . ., <A and relatively prime to A. Let
A = 2''p"'g"r* . , . , where p, q,r,. . . are distinct odd primes, and m> 0. Take
a quadratic non-residue t of p and determine a so that a=t (mod p), o=l
(mod 2qr. . .). Then a is an odd quadratic non-residue of A. Let ax=a
(mod A). For ^9^x, a, let i3?/=a (mod A). Then y^^a, x, jS. In this way
the TT numbers a, j8, . . . can be paired so that the product of the two in any
pair is =a (mod A), whence P=a''^^ (mod A).

First, let A = 2''p^ Then a'=-l (mod p"^), s = p"*-^(p-l)/2, whence
P=-l (mod^) if M = Oor L But, if m>1,

a^={-iy =l(modp'"), a^=/ =l(mod2''), P= + l(modA).

Next, let m>l, n>l, in A. Raising the above a*=— 1 to the power
2''"V~^(? — !)• • •> we get a'^^=-\-l (mod p"). A like congruence holds
moduli g", r^ . . ., and 2", whence P=4-l (mod A).

Finally, let A = 2", /x>L Then a=— 1 is a quadratic non-residue of
2" and, as above, P= ( — 1)^ (mod A),l = 2""^. The proof of Fermat's theorem
due to Ivory^^ is given by Minding on p. 32.

J. A. Grunert*^ gave Horner's^^ proof of Euler's theorem, attributing
the case of a prime to Dirichlet instead of Ivory .^^ A part of the generalized
Wilson theorem was proved as follows: Let ri,. . ., r, denote the positive
integers <p and prime to p. Let a be prime to p. In the table

riflVg, r2a^rg, . . . , rqa\

«'Abh. Ak. Wiss. Berlin (Math.), 1832, 66. Reprinted."

"Anfangsgriinde der Hoheren Arith., 1832, 75-78.

"Math. Worterbuch, 1831, pp. 1072-3; Jour, fiir Math. 8, 1832, 187.

Chap. Ill] FeKMAT's AND WiLSON's THEOREMS. 69

a single term of a row is =1 (mod p). If this term be TkO^rk, replace it
by (p—rk)a\^-l. Next, if r^^a^^ =f1, r„aVi=±l, then rk-^ri=p and
one of the r„ is replaced by p—r^. Hence we may separate riO, . . ., r^a
into q/2 pairs such that the product of the two of a pair is = ± 1 (mod p) .
Taking a = 1, we get ri . . .rg= ± 1 (mod p). The sign was determined only
for the case p a prime (by Gauss' method).

A. Cauchy^*^ derived Wilson's theorem from (1), page 62 above.
*Caraffa^^ gave a proof of Fermat's theorem.

E. Midy^^ gave Ivory's^^ proof of Fermat's theorem,

W. G. Horner^^ gave Euler's^^ proof of his theorem.

G. Libri^^ reproduced Euler's proof^^ without a reference.

Sylvester^^ gave the generalized Wilson theorem in the incomplete form
that the residue is ± 1.

Th. Schonemann^^ proved by use of symmetric functions of the roots
that if s"+6i2;""^+ ... =0 is the equation for the pth powers of the roots
of x^+aiX^~^-{- ... =0, where the a's are integers and p is a prime, then
hi=af (mod p). If the latter equation is (x — 1)'' = 0, the former is
2'*-(nP+pQ)2"-^+. ..=0, and yet is evidently (2:-l)'* = 0. Hence
71^=71 (mod p).

W. Brennecke^^ elaborated one of Gauss'^^ suggestions for a proof of the
generalized Wilson theorem. For a>2, x^=l (mod 2°) has exactly four
incongruent roots, =•= 1, ='= (l+2"~^), since one of the factors x=^l, of differ-
ence 2, must be divisible by 2 and the other by 2""^. For p an odd prime,
let ri, . . ., r^ be the positive integers <p" and prime to p", taking ri = l,
r^ = p"— 1. For 2^s^)u — 1, the root x of r^x^l (mod p") is distinct from
Ti, r^, r^. Thus 7-2, ... , r^_i may be paired so that the product of the two
of a pair is =1 (mod p"). Hence ri . . .r^= — 1 (mod p"). This holds also
for modulus 2p". For a > 2,

(2-i-i)(2»-i+l)=-l, ri. . .r^=-\-l (mod 2").

Finally, let N=p''M, where M is divisible by an odd prime, but not by p.
Then m=(f>{M) is even. The integers <N and prime to p are

rj>rj+p'^, rj+2p%.. ., r,.+(M-l)p» (i = l,. . ., m).

For a fixed j, we obtain m integers <iV and prime to N. Hence if \N\
denotes the product of all the integers < N and prime to iV,

\N\^{n. . .r^)'^=l (mod p").
ForiV = pV.-., \N\=1 (mod O,--, whence jiVt^l (modiV).

"R6suin6 analyt., Turin, 1, 1833, 35.

"Elem. di mat. commentati da Volpicelli, Rome, 1836, I, 89.

"De quelques propri^t^s des nombres, Nantes, 1836.

"London and Edinb. Phil. Mag., 11, 1837, 456.

"M6m. divers savants ac. sc. Institut de France (math.), 5, 1838, 19.

"Phil. Mag., 13, 1838, 454 (14, 1839, 47); Coll. Math. Papers, 1, 1904, 39.

"Jour, fiir Math., 19, 1839, 290; 31, 1846, 288. Cf. J. J. Sylvester, Phil. Mag., (4), 18, 1859, 281.

"Jour, fiir Math., 19, 1839, 319.

70

History of the Theory of Numbers.

[Chap. HI

A. L. Crelle^^ proved the generalized Wilson theorem. By pairing each
root <T of x-=l (mod s) with the root s—a, and each integer a<s, prime to
s and not a root, with its associated number a', where aa'=\ (mod s), we
see that the product of all the integers <s and prime to s is = + 1 or —1
(mod s) according as the number n of pairs of roots o-, s—o- is even or odd.
To find n, express s in every way as a product of two factors u, v, whose
g. c. d. is 1 or 2; in the respective cases, each factor pair gives a single root
(T or two roots. Treating four subcases at length it is shown that the num-
ber of factor pairs is 2^" in each case, where k is the number of distinct odd
primes dividing s ; and then that n is odd if s = 4, p"* or 2p", but even if n
is not of one of these three forms.

A. Cauchy^^" proved Fermat's theorem as had Leibniz.'*

V^^ (S. Earnshaw?) proved Wilson's theorem by Lagrange's method and
noted that, if Sr is the sum of the products of the roots of AqX"'+Aix"'~^-\- . . .
= 0 (mod p) taken r at a time, then AoSi — { — iyAi is divisible by p.

Paolo Gorini^" proved Euler's theorem 6'=1 (mod A), where t=(f>(A),
by arranging in order of magnitude the integers (A) p', p", . . . , p^'^ which
are less than A and prime to A. After omitting the numbers in (A) which
are di\'isible by h, we obtain a set (B) q',. . ., q^^\ Let 5^"^ be the least of
the latter which when increased by A gives a multiple of h :

(C)

g(-)+A = p^'^^6.

V

(a-1)

i(0

The numbers* (A) coincide with those in sets (B) and (D) :

(D) p%p"b,...,p^-%.

Hence by multiplication and cancellation of p',

(F) q'...qH''-^ = p^''\..p^

To each number (B) add the least multiple of A which gives a sum divisible
by b, say (G) q'+g'A,..., q^^+g^^A. The least of these is q^''^-\-A =
p^^^h, by (C). Each number (G) is <6A and all are distinct. The quo-
tients obtained by di\'iding the numbers (G) by h are prime to A and hence
included among the p^^V-j P^'\ whose number is t—a-\-l=l, so that
each arises as a quotient. Hence

(H) n(g«+^«A)=PA+g'. . .g^'^ = p'

Combine this with (F) to eliminate the p's.

pW

-a+l

q'. . .g«6''-W-"+i = PA+5'. . .q

(0

■Q

We get

6'-l = QA.

"Jour, fur Math., 20, 1840, 29-56. Abstract in Bericht Akad. Wiss. Berlin, 1839, 133-5.

»8aM6m. Ac. Sc. Paris, 17, 1840, 436; Oeuvres, (1), 3, 163-4.

"Cambr. Math. Jour., 2, 1841, 79-81.

"Annali di Fisica, Chimica e Mat. (ed., G. A. Majocchi), Milano, 1, 1841, 255-7.

*To follow the author's steps, take A = 15, 6 = 2, whence « = 8, i = 4, (A) 1, 2, 4, 7, 8, 11, 13, 14;

(B) 1, 7, 11, 13; (C) 1 + 15 = 8-2, ?(<>) =8, a = 5; (D) 2, 4, 8, 14; (F) 171113 2« = 8111314;

(G) 1 + 15,7 + 15, 11+15;13 + 15, each g = l; the quotients of the latter by 2 are 8, 11, 13,

14, viz., last four in (A); (H) P.15 + 1.7.11.13=8.11.13.14.2«; the second member ifl

1-71113 2" by (F). Hence 171113 (28-l) = 15P.

Chap. Ill] FeRMAT's AND WiLSON's THEOREMS. 71

E. Lionnet^^ proved that, if p is an odd prime, the sum of the mth powers
of 1,. . ., p — 1 is divisible by p for 0<m<p — l. Hence the sum P^ of
the products of 1, ... ,p — 1 taken w at a time is divisible by p [Lagrange^^].
Since

(l + l)(l+2)...(H-p-l) = l+Pi+P2+...H-Pp-2+(p-l)!,

l + (p — 1)! is divisible by p.

E. Catalan^^ gave the proofs by Ivory^^ and Horner.^^ C. F. Arndt^^ gave
Horner's proof; and proved the generalized Wilson theorem by associated
numbers. O. Terquem^^ gave the proofs by Gauss^^ and Dirichlet.^°

A. L. Crelle^^ republished his proof'*'' of Wilson's theorem, as well as
that by Gauss^° and Dirichlet.^° Crelle^^ gave two proofs of the generalized
Wilson theorem, essentially that by Minding^^ and that given by himself.^^
If fj, is the number of distinct odd prime factors of z, and 2^" is the highest
power of 2 dividing z, and r is a quadratic residue of z, then (p. 150) the
number n of pairs of roots ±x of x^=r (mod z) is 2""^ if m = 0 or 1, 2" if
m = 2, 2"'^^ if w>2. Using the fact (p. 122) that the quadratic residues of
z are the e=(f){z)/(2n) roots of r*=l (mod z), it is shown (p. 173) that, if v
is any integer prime to z, y*'^^^'''*=l (mod z), "a, perfection of the Euler-
Fermat theorem."

L. Poinsot^^ failed in his attempt to prove the generalized Wilson
theorem. He began as had Crelle.^^ But he stated incorrectly that the
number n of pairs of roots =^x of x^^l (mod s) equals the number v of
ways of expressing s as a product of two factors P, Q whose g. c. d. is 1 or 2.
For each pair =^x, it is implied that x—1 and x+1 uniquely determine P, Q.
For s = 24, n = y = 4; but for the root x = 7 (or for x = 17), a: ± 1 yield
P, Q = 3, 8, and 6, 4. To correct another error by Poinsot, let n be the number
of distinct odd prime factors of s and let 2"* be the highest power of 2 dividing
s; then y = 2''-^ 2", 3-2''-^ or 2"+^ according as w = 0, 1, 2, or ^3, whereas
[Crelle*^^] n = 2''-\ 2''-\ 2^ 2"+^ No difficulty is met (pp. 53-5) in case the
modulus is a power of a prime. He noted (p. 33) that if Vi, r2, . . . are the
integers <N and prime to N, and tt is their product, they are congruent
modulo N to tt/ti, Tr/ra, ..., whence T=Tr''~^ (mod N), where v=(f){N).
Thus, by Euler's theorem, 7r^= 1. This does not imply that 7r= =*= 1 as cited
by Aubry,!" pp. 30O-I.

Poinsot (p. 51) proved Euler's theorem by considering a regular polygon
of N sides. Let x be prime to N and < N. Join any vertex with the xth ver-
tex following it, the new vertex with the a:th vertex following it, etc., thus
defining a regular (star) polygon of N sides. With the same x, derive

"Nouv. Ann. Math., 1, 1842, 175-6.
«/6td., 462-4.

«Archiv Math. Phys., 2, 1842, 7, 22, 23.
"Nouv. Ann. Math., 2, 1843, 193; 4, 1845, 379.
«Jour. fur Math., 28, 1844, 176-8.
«8/bid., 29, 1845, 103-176.

«^Jour. de Math., 10, 1845, 25-30. German exposition by J. A. Grunert, Archiv Math. Phys.,
7, 1846, 168, 367.

72 History of the Theory of Numbers. [Chap. hi

similarly a new A^-gon, etc., until the initial polygon is reached.®^ The
number )U of distinct polygons thus obtained is seen to be a divisor of <t>{N),
the number of polygons corresponding to the various a:'s. If in the initial
polygon we take the x^th vertex following any one, etc., we obtain the
initial polygon. Hence of and thus also x"^^^ has the remainder unity when
divided by N. [When completed this proof differs only shghtly from that
by Euler."]

E. Prouhet^^ modified Poinsot's method and obtained a correct proof
of the generalized Wilson theorem. Let r be the number of roots of x^=l
(mod N), and w the number of ways of expressing iV as a product of two
relatively prime factors. If AT = 2'"pi" . . . p/", where the p's are distinct
odd primes, evidently w; = 2*' if m>0, 1^ = 2""^ if m = 0. By considering
divisors of a: =*= 1, it is proved that r = 2u' if ttz = 0 or 2, r = w; if w = 1, r = 4iy if
m>2. Hence r = 2" if m = 0 or 1, 2"+^ if m = 2, 2"+^ if m> 2. By Crelle,^^
the product P of the integers <A'' and prime to N is =( — 1)''''^ (mod N).
Thus for jLt>0, P= + l unless m = 0 or l,/i = l, viz., N = p^ or 2p'; while, for
^ = 0, N = 2"', m>2, we have r = 4, P=-\-l.

Friderico Arndt'^° elaborated Gauss'^^ second suggestion for a proof of
the generalized Wilson theorem. Let gf be a primitive root of the modulus
p" or 2p", where p is an odd prime. Set y=0(p"). Then g, g^,. . ., g" are
congruent to the numbers less than the modulus and prime to it. If P is
the product of the latter, P^g''-'^^^'^ But g"^=-l. Hence P=-l.
Next, if n>2, the product of the incongruent numbers belonging to an
exponent 2"""* is =1 (mod 2"). Next, consider the modulus M = AB,
where A and B are relatively prime. The positive integers < M and prime
to M are congruent modulo M to Ayi-\-Bxj, where the 0:^ are <A and prime
to A, the yi are <B and prime to B. But, if a=0(A),

a

7ri = 'n.{Ayi+BXj)=B''xi. . .Xa=Xi. . .x^ (mod A),

3 = 1

P=riTr2. ..^{x^.. .xJ'^^^Hniod A).

By resolving M into a product of powers of primes and applying the above
results, we determine the sign in P=±l (mod M).

J. A. Grunert^^ proved that if a prime n+l>2 divides no one of the
integers ai, . . ., a„, nor any of their differences, it divides aia2. . .a„+l, and
stated that this result is much more general than Wilson's theorem (the
case aj=j). But the generalization is only superficial since ai,. . ., a„ are
congruent modulo n+1 to 1,..., n in some order. His proof employed
Fermat's theorem and certain complex equations involving products of
differences of n numbers and sums of products of n numbers taken m at
a time.

J. F. Heather^^ gave without reference the first results of Grunert.^^

osCf. P. Bachmann, Die Elemente der Zahlentheorie, 1892, 19-23.

«»Nouv. Ann. Math., 4, 1845, 273-8.

"Jour, fvir Math., 31, 1846, 329-332.

"Archiv Math. Phys., 10, 1847, 312.

"The Mathematician, London, 2, 1847, 296.

Chap. Ill] FeRMAT's AND WiLSON's THEOREMS. 73

A. Lista'^^ gave Lagrange's proof of Wilson's theorem.

V. Bouniakowsky'^^ gave Euler's^^ proof.

P. L. Tchebychef^^ concluded from Fermat's theorem that

(a:-l)(x-2). . .(x-p+l)-a;^-i+l=0 (mod p)

is an identity if p is a prime. Hence if Sj is the sum of the products of 1, . . . ,
p — 1 taken j at a time, Sj=0 (i<p — 1), Sp_i= — 1 (mod p), the last being
Wilson's theorem.

Sir F. PoUock'^^ gave an incomplete statement and proof of the general-
ized Wilson theorem by use of associated numbers. Likewise futile was
his attempt to extend Dirichlet's^" method [not cited] of association into
pairs with the product = a (mod m) to the case of a composite m.

E. Desmarest" gave Euler's^^ proof of Fermat's theorem.

0. Schlomilch^^'' considered the quotient

{„p_ (») („_i)p+ («) („_2)p- . . . f/n!.

J. J. Sylvester'^* took x = l, 2,. . ., p — 1 in turn in

{x-l){x-2) . . . (x-p+l) =x^-'+A,x^-^+ . . . +A,_i,

where p is a prime. Since x^~^=l (mod p), there result p — 1 congruences
linear and homogeneous in Ai, . . . , Ap_2, Ap-i+1, the determinant of whose
coefficients is the product of the differences of 1, 2, . . . , p — 1 and hence not
divisible by p. Thus Ai=0,..., Ap_i+1=0, the last giving Wilson's
theorem.

W. Brennecke'^^ proved Euler's theorem by the methods of Horner^^
and Laplace, ^^ noting that

{a^-y=l (mod p^), (a^-i)^'=l (mod p^), ....

He gave the proof by Tchebychef ^^ and his own proof."

J. T. Graves^" employed nx=n+l (mod p), where p is a prime, and
stated that, for n = l,..., p — 1, then x=2,..., p in some order. Also
x=p ior n = p — l. Hence 2-3. . .(p — l)=p — 1 (mod p).

H. Durege^^ obtained (2) for a = x and Grunert's^^ results on the series
[m, n] by use of partial fractions for the reciprocal o( x(x — l) . . .{x — n).

E. Lottner^^ employed for the same purpose infinite trigonometric and
algebraic series, obtaining recursion formulae for the coefficients.

"Periodico Mensual Cienciaa Mat. y Fis., Cadiz, 1, 1848, 63.

T*BuU. Ac. Sc. St. P6tersbourg, 6, 1848, 205.

"Theorie der Congruenzen, 1849 (Russian); in German, 1889, §19. Same proof by J. A.

Serret, Cours d'algebre sup^riem-e, ed. 2, 1854, 324.
^«Proc. Roy. Soc. London, 5, 1851, 664.
"TMorie des nombres, Paris, 1852, 223-5.
""Jour, fur Math., 44, 1852, 348.

"Cambridge and Dublin Math. Jour., 9, 1854, 84; Coll. Math. Papers, 2, 1908, 10.
"Einige Satze aus den Anfangsgriinden der Zahlenlehre, Progr. Realschule Posen, 1855.
soBritish Assoc. Report, 1856, 1-3.
"Archiv Math. Phys., 30, 1858, 163-6.
"/bid., 32, 1859, 111-5.

74 History of the Theory of Numbers. [Chap, hi

J. Toeplitz^ gave Lagrange's proof of Wilson's theorem.

M. A. Stern^ made use of the series for log (1 — x) to show that

1+x+xH. . . =-^ = e'+*'/2+^/3+...^
l—x

Multiply together the series for e', e'*^^, etc. By the coeflBcient of x^.

p! P' (p-2)!' •••

Take p a prime. No term of s has a factor p in the denominator. Hence

(1-s) • (p-l)! = ^-tfcli^ = integer.
P

V. A. Lebesgue^^ obtained Wilson's theorem by taking x = p — l in

p X Hk+l) . . . {k-\-p-2) =x(x+l) . . . (x+p-1).
k=i

If P is a composite number ?^4, (P — 1)! is di\'isible by P. He (p. 74)
attributed Ivory's^^ proof of Fermat's theorem to Gauss, without reference.

G. L. Dirichlet^^ gave Horner's" and Euler's^^ proof of Euler's theorem
and derived it from Fermat's by the method of powering. His proof (§38)
of the generalized Wilson theorem is by associated numbers, but is some-
what simpler than the analogous proofs.

Jean Plana" used the method of powering. Let N = p^pi' .... For M
prime to N, M^~'^ = 1 +pQ. Hence

Thus for e = (p{p^pi'), M" — ! is divisible bj' p'' and p/' and hence by their
product, etc. Plana gave also a modification of Lagrange's proof of Wilson's
theorem by use of (2) ; take x=a = p — l, subtract the expansion of (1 — 1)""^
and write the resulting series in reverse order:

(p-l)!+l = (^2^)(2^-^-l)-(V)(3^-^-l)+...

-(^:D](p-2)^-^-lt + 1(p-i)''-'-if-
H. F. Talbot^^ gave Euler's^^ proof of Fermat's theorem.
J. Blissard^^" proved the last statement of Euler.^
C. Sardi^^ gave Lagrange's proof of Wilson's theorem.
P. A. Fontebasso^*^ proved (2) for x = a by finding the first term of the
ath order of differences ofy'',{y+hy,{y-\-2hy,. . . and then setting y = 0,h = l.

^'Archiv Math. Phys., 32, 1859, 104.

"Lehrbuch der Algebraischen Analysis, Leipzig, 1860, 391.

"Introd. thdorie des nombres, Paris, 1862, 80, 17.

"Zahlentheorie (ed. Dedekind), §§19, 20, 127, 1863; ed. 2, 1871; ed. 3, 1879, ed. 4, 1894.

8'Mem. Acad. Turin, (2), 20, 1863, 148-150.

"Trans. Roy. Soc. Edinburgh, 23, 1864, 45-52.

ss^'Math. Quest. Educ. Times, 6, 1866, 26-7.

"Giomale di Mat., 5, 1867, 371-6.

•"Saggio di una introd. arit. trascendente, Treviso, 1867, 77-81.

Chap. Ill] FeRMAT's AND WilSON's THEOREMS. 75

C. A. Laisant and E. Beaujeux^^ used the period ai . . .a„ of the periodic
fraction to base B for the irreducible fraction pi/q, where q is prime to B.
li P2,. . ., Pn are the successive remainders,

Bpi = aiq+p2, Bp2 = a2q+P3,. . ., Bpr, = anq+Pi.

Starting with the second equation, we obtain the period a2. . .a„ai for P2/q-
Similarly for ps/q,. . ., Pn/q- Thus the f=(p{q) irreducible fractions with
denominator q separate into sets of n each. Hence /=A;n. Since 5'*=!,
B^=l (modg).

L. Ottinger^- employed differential calculus to show that, in

P={a+d){a+2d).. . \a+ip-l)d\ =aP-i+Ci^~V-2d+C2^-V-3d2_|__ ^

3=1 q~ri-

Cr being the sum of the products of 1, 2, . . . , A; taken r at a time. Hence, if
p is a prime, C?~^ (r = 1, . . ., p — 2) is divisible by p, and

P=aP-i+c^-2d. ..{p-l)d (mod p).

For a = d = l, this gives 0=l + (p — 1)! (mod p).

H. Anton^^ gave Gauss' ^^ proof of Wilson's theorem.

J. Petersen^^ proved Wilson's theorem by dividing the circumference of
a circle into p equal parts, where p is a prime, and marking the points
1, . . ., p. Designate by 12. . .p the polygon obtained by joining 1 with 2,
2 with 3,. . ., p with 1. Rearranging these numbers we obtain new poly-
gons, not all convex. While there are p! rearrangements, each polygon can
be designated in 2p ways [beginning with any one of the p numbers as first
and reading forward or backward], so that we get (p — 1)!/2 figures. Of
these ^(p — 1) are regular. The others are congruent in sets of p, since by
rotation any one of them assumes p positions. Hence p divides (p — 1)!/2
-(p-l)/2 and hence (p-2)!-l. Cf. Cayley^o^.

To prove Fermat's theorem, take p elements from q with repetitions in
all ways, that is, in q^ ways. The q sets with elements all alike are not
changed by a cyclic permutation of the elements, while the remaining q^ — q
sets are permuted in sets of p. Hence p divides q^—q. [Cf. Perott,^^®
Bricard.i"]

F. Unferdinger^^ proved by use of series of exponentials that

2''-(';')(^-ir+(2)(^-2r-...+(-ir(^)(2-mr

' "Nouv. Ann. Math., (2), 7, 1868, 292-3.
"Archiv Math. Phys., 48, 1868, 159-185.
''Ibid., 49, 1869, 297-8.

"Tidsskrift for Mathematik, (3), 2, 1872, 64-65 (Danish).
"^Sitzungsberichte Ak. Wisa. Wien, 67, 1873, II, 363.

76 History of the Theory of Numbers. [Chap, hi

is zero ii n<m, but, if ti^tt^, equals

where

For n = m, the initial sum equals Em = rn\.

P. Mansion^® noted that Euler's theorem may be identified with a
property of periodic fractions [cf. Laisant^^]. Let N be prime to R. Taking
R as the base of a scale of notation, divide 100. . .by A^ and let gi . . .g„ be
the repetend. Then (72" — l)/iV = Q'i. . .5„. Unless the n remainders r^
exhaust the integers <N and prime to A^, we divide r/ 00. . .by A^, where
r/ is one of the integers distinct from the r,-, and obtain n new remainders r/.
In this way it is seen that n divides (p{N), so that N divides R'^'-^ — l. [At
bottom this is Euler's^* proof.]

P. Mansion^^ reproduced this proof, made historical remarks on the
theorem and indicated an error by Poinsot.^^

Franz Jorcke^^ reproduced Euler's^^ proof of Wilson's theorem.

G. L. P. V. Schaewen^^ proved (2) with a changed to —p, by expanding
the binomials.

Chr. ZeUer^o" proved that, for n ?^ 4,

is divisible by n unless n is a prime such that n — 1 divides x, in which case
the expression is = — 1 (mod n) .

A. Cayley^°^ proved Wilson's theorem as had Petersen.^^
E. Schering^^^ took a prime to m = 2'pi''\ . .p'", where the p's are dis-
tinct odd primes and proved that x^=a (mod m) has roots if and only if
a is a quadratic residue of each Pi and if a = l (mod 4) when 7r = 2, a=l
(mod 8) when 7r>2, and then has \l/{m) roots, where \p{m)=2'', 2""^^ or
2"''"^, according as 7r<2, 7r = 2, or 7r>2. Let a be a fixed quadratic residue
of m and denote the roots by ^aj (j = l,. . ., 4'/2). Set a.- =m—aj. The
<}>{m)—\f/{ni) integers <m and prime to m, other than the ay, a/, may be
denoted by aj, a/ (i = |iA+lj- • •? 20)j where aja'j=a (mod m). From the
latter and —aja/=a (i = l, . . ., ^/2), we obtain, by multiplication,
^i^(m) = (_j)}*(m)^^ .r^ (mod w),

••Messenger Math., 5, 1876, 33 (140); Xouv. Corresp. Math., 4, 1878, 72-6.

"Th6orie des nombres, 1878, Gand (tract).

•*Uber Zahlenkongruenzen, Progr. Fraustadt, 1878, p. 31.

"Die Binomial Coefficienten, Progr. Saarbriicken, 1881, p. 20.
looBull. des sc. math, astr., (2), 5, 1881, 211^.

"'Messenger of Math., 12, 1882-3, 41; CoU. Math. Papers, 12, p. 45.
iwActa Math., 1, 1882, 153-170; Werke, 2, 1909, 69-86.

Chap. Ill] FeRMAt's AND WiLSON's THEOREMS. 77

where the Vj are the integers <m and prime to m. Taking a=l, we have
the generahzed Wilson theorem. Applying a like argument when a is a
quadratic non-residue of m [Minding^^], we get

^J^(m)^^^_ .r^=(_l)^'^('») (mod m).

This investigation is a generaUzation of that by Dirichlet.*"

E. Lucas^"^ wrote Xp for x{x-\-l) . . .{x-\-p — l), and F^ for the sum of
the products of 1, . . . , p taken g at a time. Thus

^ ~rA p-i^ ~r • • • ~rA p-i^ — Xp.

Replacing p by 1, . . ., n in turn and solving, we get

where

(-l)"-^+'A„-p+i =

•plp2 pn— p+1

1 r^ Y'*~p

0 o...iri

the subscript p — 1 on the F's being dropped. After repeating the argument
by Tchebychef^^, Lucas noted that, if p is an odd prime, A„_p+i=l or 0
(mod p), according as p — 1 is or is not a divisor of n.

G. Wertheim^°^ gave Dirichlet's^^ proof of the generalized Wilson
theorem; also the first step in the proof by Arndt.^°

W. E. HeaP''^ gave without reference Euler's^'* proof.

E. Catalan^°^ noted that if 2n+l is composite, but not the square of a
prime, n\ is divisible by 2n+l; if 2n+l is the square of a prime, (n!)^ is
divisible by 2n+l.

C. Garibaldi^"^ proved Fermat's theorem by considering the number N
of combinations of ap elements p at a time, a single element being selected
from each row of the table

en ^12. . .eia

^pl ^p2 • • • ^pa.

From all possible combinations are to be omitted those containing elements
from exactly n rows, for n = l, . . ., p — 1. Let An denote the number of
combinations p at a time of an elements forming n rows, such that in each
combination occur elements from each row. Then

--iV-tO^-

"'BuU. Soc. Math. France, 11, 1882-3, 69-71; Mathesis, 3, 1883, 25-8.

i^Elemente der Zahlentheorie, 1887, 186-7; Anfangsgriinde der Zahlenlehre, 1902, 343-5

(331-2).
"'Annals of Math., 3, 1887, 97-98.

»««M6m. soc. roy. so. LiSge, (2), 15, 1888 (Melanges Math., Ill, 1887, 139).
"^Giornale di Mat., 26, 1888, 197.

78 History of the Theory of Numbers. [Chap, hi

Take each e^ = 1 ; then N = a^ smce the number of the specified combina-
tions becomes the sum of all products of p factors unity, one from each row
of the table. Thus

0"= ( ^j=a (mod p).

p-i

R. W. Genese^°^ proved Euler's theorem essentially as did Laisant.'^

M. F. Daniels^^^ proved the generahzed Wilson theorem. If ^(n)
denotes the product of the integers <n and prime to n, he proved by induc-
tion that ^(p')= — 1 (mod p') for p an odd prune. For, if pi, . . ., p„ are
the integers < p' and prime to it, then pi +jp', . . ., Pn +ip' (i = 0, 1 , . . . , p — 1)
are the integers < p'"^^ and prime to it. He proved similarly by induction
that 1/^(2') = + ! (mod 2') if 7r>2. Evidently iA(2) = l (mod 2), »//(4)=-l
(mod 4). If m = a''b^ . . . and n = l^, where I is a new prime, then \p(m)=e
(mod m), \l/{n) = r) (mod n) lead by the preceding method to \l/{mn) = e'^^"^
(mod m), viz., 1, unless n = 2. The theorem now follows easily.

E. Lucas^^^ noted that, if x is prime to n = AB . . ., where A, B,. . . are
powers of distinct primes, and if 0 is the 1. c. m. of (f){A), (l>{B),. . ., then
x'^= 1 (mod n). In case A = 2^', A:> 2, we may replace (j){A) by its half. To
get a congruence holding whether or not x is prime to n, multiply the former
congruence by x", where a is the greatest exponent of the prime factors of n.
Note that <}>-\-<T<n [Bachmann^^^' "^]. CarmichaeP^^ wrote X(n) for 0.

E. Lucas^^^ found A^~^x^~^ in two ways by the theory of differences.
Equating the two results, we have

(p-i)!=(p-ir^-(^7^)(p-2ri+...-(^:^)i

Each power on the right is = 1 (mod p) . Thus

(p-l)!=(l-l)p-i-l=-l (modp).

P. A. MacMahon^^^ proved Fermat's theorem by showing that the
number of circular permutations of p distinct things n at a time, repetitions
allowed, is

h<l>(d)p^^',

ft

where d ranges over the divisors of n. For n a prime, this gives

p"+(n — l)p=0, p"=p (mod n). ^^

Another specialization led to Euler's generalization.

E. Maillet^^^ applied Sylow's theorem on subgroups whose order is
the highest power p'' of a prime p dividing the order m of a group, viz.,

"^British Association Report, 1888, 580-1.

""Lineaire Congruenties, Diss. Amsterdam, 1890, 104-114.

""BuU. Ac. Sc. St. P6tersbourg, 33, 1890, 496.

">Mathesis, (2), 1, 1891, 11; Th^orie des nombres, 1891, 432.

""Proc. London Math. Soc, 23, 1891-2, 305-313.

"'Recherches sur les substitutions, Th§se, Paris, 1892, 115.

Chap. Ill] FeRMAT's AND WiLSON's THEOREMS. 79

'm = pN{l+np), when h = l. For the sjonmetric group on p letters, m = p\
and N = p — \, so that (p — 1)!= — 1 (mod p). There is exhibited a special
group for which m = pa^, N = a, whence a^=a (mod p).

G. Levi"* failed in his attempt to prove Wilson's theorem. Let b and
a={p — l)h have the least positive residues ri and r when divided by p.
Then r+ri = p. Multiply h/p = q+ri/p by p — 1. Thus ri(p — 1) has the
same residue as a, so that

Ci T

ri(p-l)=r+mp, - = q{p-l)+m+-

He concluded that ri(p — l)=r, falsely, as the example p = 5, 6 = 7, shows.
He added the last equation to r+ri = p and concluded that ri = l, r = p — l,
so that (a+l)/p is an integer. The fact that this argument is independent
of Levi's initial choice that 6 = (p — 2) ! and his assumption that p is a prime
shows that the proof is fallacious.

Axel Thue"^ obtained Fermat's theorem by adding

a''-{a-iy = l+kp, {a-iy-{a-2y = l+hp, ..., P-0^=1

[PaoU*^]. Then the differences A^i^(j) of the first order of F{x)=x^~'^ are
divisible by p for J = 1,. . ., p-2; likewise A^/^(l),. . .,^''-^F{l), By adding

A^+i/r(o)=A^F(l)-A^(0) (i = l,. . ., p-2),

we get

-A^-^/?'(0) = 1+AV(1)-A2/?'(1)+. . .+A^-2F(1), (p-l)!+l=0(modp).

N. M. Ferrers"® repeated Sylvester's"^^ proof of Wilson's theorem.
M. d'Ocagne"^ proved the identity in r:

(r+l)^+i+^^i^SPfcl^PV(^+l)'^'"''(-0*'=r'+' + l,

where g = [(A;+l)/2] and P^"^ is the product of n consecutive integers of
which m is the largest, while P^ = L Hence if /c+1 is a prime, it divides
(j,_[_j)A:+i_^fc+i_2^ and Fermat's theorem follows. The case k = p — l
shows that if p is a prime, q={p — l)/2, and r is any integer,

S P%-.^i PV(^+l)''"''(-^)*=0 (mod g!).
t=i

T. del Beccaro"^ used products of linear functions to obtain a very com-
pUcated proof of the generalized Wilson theorem.

A. Schmidt"^ regarded two permutations of 1, 2, . . ., p as identical if
one is derived from the other by a cyclic substitution of its elements. From
one of the (p — 1)! distinct permutations he derived a second by adding

"*Atti del R. Istituto Veneto di Sc, (7), 4, 1892-3, pp. 1816-42.

"'Archiv Math, og Natur., Kristiania, 16, 1893, 255-265.

'"Messenger Math., 23, 1893-4, 56.

"^Jour. de I'^cole polyt., 64, 1894, 200-1.

"8Atti R. Ac. Lincei (Fis. Mat.), 1, 1894, 344-371.

""Zeitschrift Math. Phys., 40, 1895, 124.

80 History of the Theory of Numbers. [Chap, hi

unity to each element and replacing p+1 by 1. Let m be the least number
of repetitions of this process which will yield the initial permutation. For
p a prime, m = l or p. There are p — 1 cases in which m = \. Hence
(p — 1) ! — (p — 1) is divisible by p. Cf . Petersen.^^
Many proofs of (3), p. 63, have been given. ^^°

D. von Sterneck^-^ gave Legendre's proof of Wilson's theorem.

L. E. Dickson^-^ noted that, if p is a prime, p(p — 1) of the p! substitu-
tions on p letters have a linear representation x'=ax-\-h, a^O (mod p),
while the remaining ones are represented analytically by functions of degree
> 1 which fall into sets of p^(p — 1) each, viz., aJ{x-^h)-\-c, where a is prime
top. Hencep!—p(p — l) is a multiple of p^(p — l), and therefore (p — 1)!+1
is a multiple of p.

C. Moreau^-^ gave without references Schering's^°^ extension to any
modulus of Dirichlet's^° proof of the theorems of Fermat and Wilson.

H. Weber^'^ deduced Euler's theorem from the fact that the integers
Km and prime to m form a group under multiplication, whence every
integer belongs to an exponent dividing the order 0(m) of the group.

E. Cahen^-^ proved that the elementary symmetric functions of 1,. . .,
p — 1 of order <p — 1 are divisible by the prime p. Hence

(a:-l)(a:-2). . .(a:-p+l)=xP-^+(p-l)! (modp),

identically in x. The case x = l gives Wilson's theorem, so that also Fer-
mat's theorem follows.

J. Perott^-^ gave Petersen's^^ proof of Fermat's theorem, using q^ ''con-
figurations" obtained by placing the numbers 1, 2,..., q into p cases,
arranged in a line. It is noted that the proof is not vaUd for p composite;
for example, if p = 4, g = 2, the set of configurations derived from 1212 by
cyclic permutations contains but one additional configuration 2121.

L. Kronecker^^^ proved the generalized Wilson theorem essentially as
had Brennecke.^^

G. Candido^^^ made use of the identity

aP+6P= (a+6)P-pa6(a+6)P-2+ . . .

^^_^).p(p-2r+10...(p-r-l) .,,_^ ^^^

1-2. . .r

Take p a prime and 6= —1. Thus a^ — a=(a — 1)^— (a — 1) (mod p).

"«L'mterm6diaire des math., 3, 1896, 2&-28, 229-231; 7, 1900, 22-30; 8, 1901, 164. A. Capelli

Giornale di Mat., 31, 1893, 310. S. Pincherle, ibid., 40, 1902, 180-3.
"iMonatshefte Math. Phys., 7, 1896, 145.
»»Annals of Math., (1), 11, 1896-7, 120.
i"Nouv. Ann. Math., (3), 17, 1898, 296-302.
i^Lehrbuch der Algebra, II, 1896, 55; ed. 2, 1899, 61.
^"£l6ment3 de la throne des nombres, 1900, 111-2.
>»'Bull. des Sc. Math., 24, I, 1900, 175.
i"Vorlesungen uber Zahlentheorie, 1901, I, 127-130.
"'Giomale di Mat., 40, 1902, 223.

Chap. Ill] FeRMAT's AND WiLSON's THEOREMS. 81

P. Bachmann^^^ proved the first statement of Lucas."*' He gave as a
"new" proof of Euler's theorem (p. 320) the proof by Euler,^^ and of the
generaUzed Wilson theorem (p. 336) essentially the proof by Arndt.^°

J. W. Nicholson^^^ proved the last formula of Grunert.^^

Bricard^^^ changed the wording of Petersen's^^ proof of Fermat's theorem.
Of the q^ numbers with p digits written to the base q, omit the q numbers
with a single repeated digit. The remaining q^—q numbers fall into sets
each of p distinct numbers which are derived from one another by cyclic
permutations of the digits.

G. A. Miller^^^ proved the generalized Wilson theorem by group theory.
The integers relatively prime to g taken modulo g form under multiplica-
tion an abelian group of order (f){g) which is the group of isomorphisms of a
cyclic group of order g. But in an abelian group the product of all the ele-
ments is the identity if and only if there is a single element of period 2.
It is shown that a cyclic group is of order p", 2p* or 4 if its group of isomor-
phisms contains a single element of period 2.

V. d'Escamard^^^ reproduced Sylvester's''^ proof of Wilson's theorem.

K. Petr^^* gave Petersen's®^ proof of Wilson's theorem.

Prompt^^® gave an obscure proof that 2^~^ — 1 is divisible by the prime p.

G. Arnoux^^® proved Euler's theorem. Let X be any one of the
v=4>{m) integers a, /3, 7, . . ., prime to m and <m. We can solve the con-
gruences

aa'=/3/3'=77'= . . . =\ (mod m).
Here a', jS', . . .form a permutation of a, |S, . . . . Thus

In particular, for X = l, we get (a/3. . .)^=1. Hence for any X prime to m,
V=\ (mod m). [Of. Dirichlet/" Schering,i°2 C. Moreau.i^^]

R. A. Harris^^^" proved that (aj8 . . .)^ = 1 as did Arnoux^^^, but inferred
falsely that a./3 . . . = ± 1.

A. Aubry^^'^ started, as had Waring in 1782, with

where yp = a:(a; — 1). . .(x— p+1). Then

x'»+i-a;'^= F„+i+A7„+ . . . -I-MF3+F2.
Summing for x = 1, . . . , p — 1 and setting Sk = l*+2*+ . . . + (p — 1)*, we get

_\n±l\_ \n\ , ,MJ3J , \2\

n+2 w+1

«»Niedere Zahlentheorie, I, 1902, 157-8. ""Amer. Math. Monthly, 9, 1902, 187, 211.

"iNouv. Ann. Math., (4), 3, 1903, 340-2.

"2Annals of Math., (2), 4, 1903, 188-190. Cf. V. d'Escamard, Giornale di Mat., 41, 1903,

203-4; U. Scarpis, ihid., 43, 1905, 323-8.
»"Giomale di Mat., 43, 1905, 379-380. i=^Casopis, Prag, 34, 1905, 164.

^"Remarques sur le theorSme de Fennat, Grenoble, 1905, 32 pp.
"'Arithm^tique Graphique; Fonctions Arith., 1906, 24.
i»««Math. Magazine, 2, 1904, 272. "'L'enseignement math., 9, 1907, 434-5, 440.

82 History of the Theory of Numbers. [chap. hi

where \k\ =p{p — l) . . .(p — k). Hence, if p is a prime and n<p — 1,
Sn+i—Sn—0. But Si^O. Hence s„=0(n<p — 1), Sp_i= — (p — 1)!. Thus
Wilson's theorem follows from Fermat's.

Without giving references, Aubry (p. 298) attributed Horner's" proof
of Euler's theorem to Gauss; the proof (pp. 439-440) by Paoli^^ (and
Thue^^^) of Fermat's theorem to Euler^^; the proof (p. 458) by Laplace^^ of
Euler's theorem by powering to Euler.

R. D. CarmichaeP^^ noted that, if L is the 1. c. m. of all the roots z of
0(2) = a, and if a: is prime to L, then a:°= 1 (mod L). Hence except when n
and n/2 are the only numbers whose </)-function is the same as that of n,
^•pM = ^ holds for a modulus M which is some multiple of n. A practical
method of finding M is given.

R. D. CarmichaeP^^ proved the first result by Lucas.^^°

J. A. Donaldson^^° deduced Fermat's theorem from the theory of
periodic fractions.

W. A. Lindsay"^ proved Fermat's theorem by use of the binomial
theorem.

J. I. Tschistjakov"^ extended Euler's theorem as had Lucas. ^^°

P. Bachmann^^^ proved the remarks by Lucas,^^° but replaced <f>+(r<n
by 71^0 +(7, stating that the sign is > if n is divisible by at least two distinct
primes.

A. Thue^^ noted that a different kinds of objects can be placed into n
given places in o" ways. Of these let 11'^ be the number of placings such
that each is converted into itself by not fewer than n applications of the
operation which replaces each by the next and the last by the first. Then
U2 is divisible by n. If n is a prime, 1/1 = a""— a and we have Fermat's
theorem. Next, a''=2[/a, where d ranges over the divisors of n. Finally,
if p, 5, . . . , r are the distinct prime factors of n,

C/^=S(-l)?a"/^=0 (mod n),

where D ranges over the distinct divisors oi pq. . .r, while 0 is the number
of prime factors of D. Euler's theorem is deduced from this.

H. C. PockUngton^^^ repeated Bricard's^^^ proof.

U. Scarpis^^^ proved the generalized Wilson theorem by a method similar
to Arndt's.^° The case of modulus 2^" (X>2) is treated by induction.
Assume that Ilr=l (mod 2^), where ri, . . ., r„ are the v=4>{2^) odd integers
<2^. Then rj, . . ., r„ ri+2^, . . ., r„+2'' are the residues modulo 2^"+^ and
their product is seen to be =1 (mod 2''"''^). Next, let the modulus be

"«BuU. Amer. Math. Soc, 15, 1908-9, 221-2.

"'/bid., 16, 1909-10, 232-3.

""Edinburgh Math. Soc. Notes, 1909-11, 79-84.

"i/bwf., 78-79.

"^Tagbl. XII Vers. Russ. Nat., 124, 1910 (Russian).

i«Niedere Zahlentheorie, II, 1910, 43-44.

'*^Skrifter Videnskaba-Selskabet, Christiania, 1910, No. 3, 7 pp.

>«Nature, 84, 1910, 531.

i«Periodico di Mat., 27, 1912, 231-3.

Chap. Ill] FeEMAT's AND WiLSON's ThEOKEMS. 83

n = pi' . . .p^'* {h>2), n9^2p^. Then a system of residues modulo n, each

h

prime to n, is given by S A,r„ with

i=l

A

' w)

n \</>(pi°0

}

where r^ ranges over a system of residues modulo pi"', each prime to p,.
Let P be the product of these SA,rj. Since AiAj is divisible by n if iT^j,

h <p(n/pi°-i\

p_2Ai^W(nr,)^ ^ (modn).
t=i

Thus P— 1 is divisible by each p°^ and hence by n.

*Illgner^^^ proved Fermat's theorem.

A. Bottari^^^ proved Wilson's theorem by use of a primitive root [Gauss^°].

J. Schumacher^^^ reproduced Cayley's^°^ proof of Wilson's theorem.

A. Arevalo^^° employed the sum /S„ of the products taken n at a time of
1, 2, . . . , p — 1. By the known formula

it follows by induction that Sn is divisible by the prime p if n<p — 1. In
the notation of Wronski, write a^^*" for

a{a+r).. . \a+ip-l)r\ =a''-\-Sia''-''r+ . . .+Sp_iar^-\

For a = r = l, we have p! = l+*Si+. . .-\-Sp^i, whence >Sp_i= — 1 (mod p),
giving Wilson's theorem. Also, a^^''=a^—a'r^~^. Dividing by a and taking
r = l, we have

(a+l)(^-^^/^=a^-i-l (modp).

The left member is divisible by p if o is not. Hence we have Fermat's
theorem. Another proof follows from Vandermonde's formula

(x+ay^'= S (J)x^p-''^^'a^^'=x''^'+a''^' (mod p),
(xi + . . . +xy'-=x,^/'+ . . . +a^/^ a^/''=a-P^

Remove the factor a and set r = 0; we obtain Fermat's theorem.

Prompt^^^ gave Euler's^^ proof of his theorem and two proofs of the type
sketched by Gauss of his generalization of Wilson's theorem; but obscured
the proofs by lengthy numerical computations and the use of unconven-
tional notations.

F. Schuh^^^ proved Euler's theorem, the generalized Wilson theorem,
and discussed the symmetric functions of the roots of a congruence for a
prime modulus.

"^Lehrsatz uber x"— x, Uaterrichts Blatter fiir Math. u. Naturwisa., Berlin, 18, 1912, 15.

'"II Boll. Matematica Gior. Sc.-Didat., 11, 1912, 289.

'"Zeitschrift Math.-naturwiss. Unterricht, 44, 1913, 263-4.

""Revista de la Sociedad Mat. Espafiola, 2, 1913, 123-131.

"'Demonstrations nouvelles des th^orlmes de Fermat et de Wilson, Paris, Gauthier-Villars,

1913, 18 pp. Reprinted in Tinterm^diaire des math., 20, 1913, end.
"^Suppl. de Vriend der Wiskunde, 25, 1913, 33-59, 143-159, 228-259.

84 History of the Theory of Numbers. [Chap, hi

G. Frattini^^ noted that, if F{a, j3, . . . ) is a homogeneous symmetric
poljTiomial, of degree g with integral coefficients, in the integers a, /3, . . .
less than m and prime to m, and if F is prime to 7??, then k°= 1 (mod m) for
ever>' integer A- prime to m. In fact,

F(a, jS,. . .) = F{ka, k^,.. .) = k^F{a, 0,...) (mod m).

Taking F to be the product a^. . ., we have Euler's theorem. Another
corollary is

u\l+j)=l + (p-l)l (modp),

for p a prime, which implies Wilson's theorem.

*J. L. Wildschlitz-Jessen^^^ gave an historical account of Fermat's and
Wilson's theorems.

E. Piccioh^" repeated the work of Dirichlet.'*°

The Generalization F{a,N) = 0 (mod N) of Fermat's Theorem.
C. F. Gauss^^° noted that, if N=pi^ . . .p/* (p's distinct primes),

»=1 »■<;■ x<i<k

is divisible by N when a is a prime, the quotient being the number of irre-
ducible congruences modulo a of degree N and highest coefficient unity.
He proved that
(1) a^=2F(a, d), F{a,\)=a,

where d ranges over all the divisors of N, and stated that this relation read-
ily leads to the above expression for F (a, N). [See Ch. XIX on inversion.]

Th. Schonemann^^^ gave the generalization that if a is a power p" of a
prime, the number of congruences of degree A^ irreducible in the Galois field
of order a is N~'^F{a, N).

An account of the last two papers and later ones on irreducible con-
gruences will be given in Ch. VIII.

J. A. Serret^^^ stated that, for any integers a and iV, F{a, N) is divisible
by N. For N=p\ p a prime, this implies that

a</>(pO = l (modpO,

when a is prime to p, a case of Euler's theorem.

S. Kantor^^^ showed that the number of cycHc groups of order N in any
birational transformation of order a in the plane is N~^F{a, N) . He obtained
(1) and then the expression for F(a, N) by a lengthy method completed for
special cases.

iwPeriodico di Mat., 29, 1913, 49-53.

i^Nyt Tidsskrift for Mat., 25, A, 1914, 1-24, 49-68 (Danish).

i"Periodico di Mat., 32, 1917, 132-4.

"oPosthumous paper, Werke, 2, 1863, 222; Gauss-Maser, 611.

"iJour. fiir Math., 31, 1846, 269-325. Progr. Brandenburg, 1844.

i"Nouv. Ann. Math., 14, 1855, 261-2.

"'AnnaU di Mat., (2), 10, 1880, 64-73. Comptes Rendus Paris, 96, 1883, 1423.

Chap. Ill] GENERALIZATIONS OF FeRMAT's THEOREM. 85

Ed. Wey^^^^ E. Lucas^^^ and Pellet^^^ gave direct proofs that F{a, N) is
divisible by N for any integers a, N.

H. Picquet^^^ noted the divisibility of F{Zm — l, N) by iV in an enumera-
tion of certain curvilinear polygons of N sides, at the same time inscribed
and circumscribed in a given cubic curve. He. gave a proof of the divisi-
bility of F{a, N) by N, requiring various subcases. He stated that the
function F{a, N) is characterized by the two relations

(2) F{a, np") ^F{a''\ n) -F{a''"\ n), F^a, p')=a^'-a''"\

where a is any integer, n an integer not divisible by the prime p.
A. Grandi^®^ proved that F{a, N) is divisible by N by writing it as

^N _ ^N/p, _ j ^^N/p, _ ^Nlp,p,-^ j^ ^^N/p, _ ^N/p,v,^ + . . . [

+ \ {a^/p^P'-a^/PiP^p>) -f- ... J -I- ... .
Each of these binomials is divisible by pi' since

G. Koenigs^^* considered a uniform substitution z' =4>{z) and its nth
power z" =4)n{z). Those roots of 2— 0^(2) =0 which satisfy no like equation
of lower index are said to belong to the index n. If x belongs to the index
n, so do also (^i{x) for i—\,..., n — 1. Thus the roots belonging to the
index n are distributed into sets of n. If a is the degree of the polynomials
in the numerator and denominator of 0(s), the number of roots belonging
to the index n is F{a, n), which is therefore divisible by n.

MacMahon's^^^ paper contains in a disguised form the fact that F(a, N)
is divisible by N. Proofs were given by E. Maillet"^ by substitution
groups, and by G. Cordone.^^^

Borel and Drach^'^" made use of Gauss' result that F{p, N) is divisible
by N for every prime p and integer N, and Dirichlet's theorem that there
exist an infinitude of primes p congruent modulo N to any given integer a
prime to N, to conclude that F(a, N) is divisible by N.

L. E. Dickson^^^ proved by induction (from k to k-{-l primes) that
F{a, N) is characterized by properties (2) and concluded by induction that
F{a, N) is divisible by N. A like conclusion was drawn from

\F{a, N)\'-F{a, N)=Fia, qN) (mod q),
where g is a prime. He gave the relations

F{a, nN) = Fia"", n) - i F(a^/^-, n) + S Fia"^^"'"', n)-...

+ {-TyF{a^^'''-'", n)l
F{a,N)=i:<l>id),

"Casopis, Prag, 11, 1882, 39.

""Comptes Rendus Paris, 96, 1883, 1300-2.

»«/6td., p. 1136, 1424. Jour, de I'^cole polyt., cah. 54, 1884, 61, 85-91.

i"Atti R. Istituto Veneto di Sc, (6), 1, 1882-3, 809.

i"Bull. des sciences math., (2), 8, 1884, 286.

"•Rivista di Mat., Torino, 5, 1895, 25.

""Introd. th^orie dea nombres, 1895, 50.

"^Annals of Math., (2), 1, 1899, 35. Abstr. in Comptes Rendus Paris, 128, 1899, 1083-6.

86 History of the Theory of Numbers. [Chap, hi

where d ranges over those divisors of a^ — 1 which do not divide d° — l for
0<t;<iV; while, in the former, Pi,. . ., Pa are the distinct prime factors of
N, and n is prime to N.

L. Gegenbauer^^- wrote F(o, n) in the form S/i(c^)a"'''', where d ranges
over the divisors of n, and nid) is the function discussed in Chapter XIX
on Inversion. As there shown, 2ju(d) =0 if n> 1. This case fix) =ijl{x) is
used to prove the generaUzation : If the function /(x) has the property that
2/((i) is divisible by n, then for every integer a the function l!>f{d)a'''^ is
divisible by n, where in each sum d ranges over the divisors of n. Another
special case, f{x) =4>{x), was noted by MacMahon.^^^

J. Westlund^^^ considered any ideal Am. o. given algebraic number field,
the distinct prime factors Pi, . . . , P^ of ^, the norm n(^) of ^, and proved
that if a is any algebraic integer,

^nU) _^gn{A)ln{Pi) _|_2^n(^)/n(PiPj) _ 4- ( — n'^'>(^)/«(Pi. . -Pi)

is always divisible by A.

J. Vdlyi^^^ noted that the number of triangles similar to their nth pedal
but not to the dih. pedal {d<n) is

Xin) =^P{n) -^^(^) +2'A(-^) - ■ ■ .,

Vp/ ^PlP2^

if Pi> P2, • • • are the distinct prime factors of n, and yp{k)=2^{2^ — \). He
proved that x(^) is divisible by n, since if the nth pedal to ABC is the first
one similar to ABC, a like property is true of the first pedal, . . ., (n — l)th
pedal, so that the x(^) triangles fall into sets of n each of period n. [Note
that x(n)=P(4, n)-F(2, n).]

A. Axer^^^ proved the following generalization of Gegenbauer's"^ theorem:
If G(ri, . . . , r/i) is any polynomial with integral coefficients, and if, when d
ranges over all the divisors of n,

2/(rf)G(ri"^. . ., rC'^)=Q (mod n)

for a particular function G = Gq and a particular set of values Txq, . . . , r/,o,
not a set of solutions of Gq, and for which Go is prime to n, then it holds for
every G and every set ri, . . . , r^.

Further Generalizations of Fermat's Theorem.

For the generalization to Galois imaginaries, see Ch. VIII.

For the generalization by Lucas, see Ch. XVII, Lucas,^^ Carmichael.^'

On :x^= 1 (mod n) for x prime to n, see Cauchy,^^ Moreau,^^ Epstein,"'
of Ch. VII.

0. H. MitchelP'^ considered the 2* products s of distinct primes dividing
k = pi...pf and denoted by r/A;) the number of positive integers
X,<k which are divisible by s but by no prime factor of k not dividing s.

i^Monatshefte Math. Phys., 11, 1900, 287-8.

i"Proc. Indiana Ac. Sc, 1902, 78-79.

"«Monatshefte Math. Phys., 14, 1903, 243-2.53.

»"MonatBhefte Math. Phys., 22, 1911, 187-194.

"»Amer. Jour. Math., 3, 1880, 300; Johns Hopkins Univ. Circular, 1, 1880-1, 67, 97.

Chap. Ill] GENERALIZATIONS OF FeRMAt's THEOREM. 87

The products of the various X^ by any one of them are congruent modulo k
to the Xg in some order. Hence

X/^w=ie^ (modifc),

where R^ is the corresponding one of the 2' roots of x^^x (mod k). The
analogous extension of Wilson's theorem is HXs^^Rs (mod k), the sign
being minus only when k/a = p'', 2p' or 4 and at the same time a/s is odd.
Here <r = np/^ if s = np,. Cf. Mitchell,^" Ch. V.

F. RogeP^^ proved that, if p is a prime not dividing n,

n-i = l+(f)(7i-l) + (|)(n-l)2+... + (f)(n-l)Hp, A: = ^,

where p is divisible by every prime lying between k and p+l.

Borel and Drach^^° investigated the most general polynominal in x divis-
ible by m for all integral values of x, but not having all its coefficients
divisible by m. If m = p''q^, . . . , where p, q,. . .are distinct primes, and if
P{x), Q{x),. . . are the most general polynomials divisible by p", q^,. . .,
respectively, that for m is evidently

{P{x)+p'^f{x)\\Q{x)+q'g{x)\....

For a<p+l, the most general P{x) is proved to be

iMx)Mx), Mx) =p''-\x^-x)\

where the/'s are arbitrary polynomials. For a<2(p+l), the most general
P{x) is

s/,<A,+ ste, rp,=ct>{x){x^-xy-Y-''-\

k=l k=l

where 4>{x) = {x^—xy—p^~^{x^—x), and the/'s, g's are arbitrary poly-
nomials. Note that ^^(x) -p'''-'^<f>lx) is divisible by p^'+^+K Cf. Nielsen.^^^
E. H. Moore^^^ proved the generalization of Fermat's theorem:

Xi''"*-^ X p*""^

XiP
Xi

m p— 1 p— 1

= n H . . . H {Xk+Ck+iXk+i+ . . . +c^xj (mod p).

F. Gruber^^^ showed that, if n is composite and ai, . . . , a< are the ^=0(n)
integers < n and prime to n, the congruence

(1) x' — l = (x— fli). . .(x— a«) (mod n)

is an identity in x if and only if n = 4 or 2p, where p is a prime 2*+l.

"•Archiv Math. Phys., (2), 10, 1891, 84-94 (210).

""Introduction th^orie des nombres, 1895, 339-342.

">BuU. Amer. Math. Soc, 2, 1896, 189; cf. 13, 1906-7, 280.

"»Math. Nat. Berichte aus Ungarn, 13, 1896, 413-7; Math, term^s ertesito, 14, 1896, 22-25.

88

History of the Theory of Numbers.

[Chap. Ill

E. Malo^^ employed integers -4/ and set u = afz,

Since f^ d='Eu''/k {k = n, m+n, 2m-\-n,

e=

w

l-u"

=ScOpX''-Ma:.

2^x^=2^^'^'

P

k

p k

p-ltkt

where k takes the values n, w+n, . . .which are ^p/fi. If no prime factor
of such a k occurs in the denominator of the expansion of cop/p, the latter
is an integer; this is the case if p is a prime and /x= 2. For w = n = l, ix = 2,

^(»-)-(2)-(3)-

+

■ax

a-3.

.0-2

we get o3p = a^—a and hence Fermat's theorem.

L. Kronecker^^ generalized Fermat's and Wilson's theorems to modular
systems.

R. Le Vavasseur^^ obtained a result evidently equivalent to that by
Moore^^^ for the non-homogeneous case Xm = l'

M. Bauer^^^ proved that if n = p'm, where m is not divisible by the odd
prime p, and Oi, . . ., a< are the t=<l>{n) integers <n and prime to n,

{x-ai) . . .(a:-a,) = (xP-i-l)'/<P-'Hmod p'),

identically in a:. If p = 2 and 7r> 1, the product is identically congruent to
{x'^ — iy^^. Hence he found the values of d, n for which (1) holds modulo d,
when d is a divisor of n. If p denotes an odd prime and q a prime 2*+ 1, the
values are

d

2q

4

P

2

n

2q

4

p-, 2p»

2^2"5lg2...

M. Bauer^*'' determined how n and N must be chosen so that x" — 1
shall be congruent modulo A^ to a product of linear functions. We may
restrict N to the case of a power of a prime. If p is an odd prime, a;" — !
is congruent modulo p° to a product of linear functions only when p=l
(mod n), a arbitrary, or when n = p'm, a = l, p = l (mod m). For p = 2,
only when n = 2^, a = l, or n = 2, a arbitrary. For the case n a prime, the
problem was treated otherwise by Perott.^^^

M. Bauer^^^ noted that, if n = 'p'm, where m is not divisible by the odd
prime p,

n(a:-i) = (xP-x)"/P (mod p').

t=i

>8»L'interm6diaire des math., 7, 1900, 281, 312.
^"Vorlesungen uber Zahlentheorie, I, 1901, 167, 192, 220-2.

'"Comptes Rendus Paris, 135, 1902, 949; Mdm. Ac. Sc. Toulouse, (10), 3, 1903, 39-48.
•"Nouv. Ann. Math., (4), 2, 1902, 256-264.

"'Math. Nat. Berichte aus Ungarn, 20, 1902, 34-38; Math. 6s Phys. Lapok, 10, 1901, 274-8
(pp. 145-152 relate to the "theory of Fermat's congruence"; no report is available).
"8Amer. Jour. Math., 11, 1888; 13, 1891.
'"Math. 68 Phys. Lapok, 12, 1903, 159-160.

Chap. Ill] GENERALIZATIONS OF FeRMAT's ThEOREM. 89

Richard Sauer^^'^ proved that, \i a,h, a — h are prime to k,

a^+a^-^6+a^-V+ • • • +?)*'=1 (mod k), <P = (p{k),

since a*""^^— 6*"^^=a— 6. Changing alternate signs to minus, we have a
congruence valid if a, 6 are prime to k, and if 0+6 is not divisible by k.
If p is an odd prime dividing a=F6,

is divisible by p, but not by p^.

A. Capelli^^^ showed that, if a, 6 are relatively prime.

ah

=[V]+[V]+i'

where [x] is the greatest integer ^ x.

M. Bauer^^^ proved that, if p is an odd prime and m = p" or 2p^, every
integer x relatively prime to m satisfies the congruence

(a;p-i _ l)p"- = (x+A^i) . . . {x-\-ki) (mod m),

where /bi, . . ., ki denote the l=<l){m) integers <m and prime to m>2. If
m is not 4, p" or 2p", every integer a: prime to m satisfies the congruence

(x^^-^y^-iy^(x+ki) . . . (x+ki) (mod m).

L. E. Dickson^^^ proved Moore's^^^ theorem by invariantive theory.

N. Nielsen^^^ proved that, if ^{x) is a polynomial with integral coeffi-
cients not having a common factor > 1, and if for every integral value of x
the value of ^{x) is divisible by the positive integer m, then

p-i
^{x) = (f>{x) o)p{x)+ S rrip-s A, cos(x), o)n{x)=x{x-\-l) . .{x+n-1),

8= 1

where 4>(x) is a polynomial with integral coefficients, the Ag are integers,
p is the least positive integer for which p ! is divisible by m, and mp_s is
the least positive integer I for which s\l is divisible by m. Cf. Borel and
Drach.i8°

H. S. Vandiver^^^ proved that, if V ranges over a complete set of incon-
gruent residues modulo m = pi . . .pl^, while U ranges over those F's
which are prime to m,

A;

ll{x-V)^^tXx''^-xT"'% n(a;-C7)=Si,(a;P«-'-l)*'('")/(p»-^>,

modulo w, where t^ = {mlpg^^y, e = </)(p/») . For w = p", the second congruence
is due to Bauer.^^^' ^^^

""Eine polynomische Verallgemeinerung des Fermatschen Satzes, Diss., Giessen, 1905.

»"Dritter Internat. Math. Kongress, Leipzig, 1905, 148-150.

»»Archiv Math. Phys., (3), 17, 1910, 252-3. Cf. Bouniakowsky^s of Ch. XI.

"'Trans. Amer. Math. Soc, 12, 1911, 76; Madison Colloquium of the Amer. Math. Soc, 1914,

39-40.
"<Nieuw Archief voor Wiskunde, (2), 10, 1913, 100-6.
i»Annals of Math., (2), 18, 1917, 119.

90 History of the Theory of Numbers. [Chap, hi

Further Generalizations of Wilson's Theorem; Related Problems.

J. Steiner-°° proved that, if Ak is the sum of all products of powers of
Gi, 02,..., Op-it of degree k, and the o's have incongruent residues p^O
modulo p, a prime, then A^,. . ., Ap_2 are divisible by p.

He first showed by induction that

z =2i.p^i-\-AiA.p^2~T' ■ ■ ■ \Ap-2-^i\Ap^i,
Xk={x-ai). . .{x-ttk), ^i = Oi+. . .+ap_i,

^2 = 01^ + 0102+ . . . +0iOp_2 + O2^+O2O3+ . . . +oJ_2,

For example, to obtain x^ he multipUed the respective tenns of

V=(X — Oi)(x — 02) + (01+02) (x — 0i)+0i^

by X, (a:-03)+a3, (x— 02)+02, (x — oO+Oi. Let Oi,..., Op_i have the
residues 1,. . ., p — l in some order, modulo p. For x — 02 divisible by p,
x^~^=Ap_i = a{~^ (mod p), so that Ap_2Xi and hence also Ap_2 is divisible
by p. Then for x=a3, ^p_3X2 and ^p_3 are divisible by p. For x = 0,
ai = l, the initial equation yields Wilson's theorem.

C. G. J. Jacobi"''^ proved the generahzation : If Oi,. . ., a„ have distinct
residues f^ 0, modulo p, a prime, and Pr^m is the sum of their multipUcative
combinations with repetitions m at a time, Pnm is divisible by p for w = p— n,
p-n+1,..., p-2.

Note that Steiner's Ah is Pp-k.k- We have

][ J^ I Pfil ■ Pn2

(x-oi) . . . (x-o„) "x""^x"+i^x"+2"^ • • •' ' """,=;

(1) 7:r^7v^^^^.=i+9h+^2+--: P..= :^a;^-'/Dj,

Dj = {cLj - Oi) . . . (Oj - a,_i) (oy - Oy+i) . . . (o, - 0 J , 0=2 Oy /D, {k<n-l).

j=i

Let n+m-l = k+^{p-\). Then o^+^-^^o/ (mod p). Hence if
A;<Cn — 1

' Di . . .Dr,Pn,„=D, . . .Dj:a)/D„ P^^^O (mod p).

The theorem follows by taking /3 = 1 and ^' = 0, 1, . . ., n— 2 in turn.

H. F. Scherk^°- gave two generaUzations of Wilson's theorem. Let p be
a prime. By use of Wilson's theorem it is easily proved that

n!

where x is an integer such that px=l (mod n!). Next, let C/ denote the
sum of the products of 1, 2, . . . , ^ taken r at a time with repetitions. By use
of partial fractions it is proved that

(p-r-l)!C;_,_i+(-l)'-=0(modp) (r<p-l).

It is stated that

""Jour, fiir Math., 13, 1834, 356; Werke 2, p. 9.
""/bid., 14, 1835, 64-5; Werke 6, 252-3.

'"Bericht iiber die 24. Versammlung Deutscher Naturforscher und Aerzte in 1846, Kiel,
1847, 204-208.

(p-n-l)!^(-ir^^(modp),

Chap. Ill] Genekalizations OP Wilson's Theorem. 91

C;.r-iCr-' + {-iy^O, C:,-m\^0 (modp), ^ = ^-

H. F. Scherk^''^ proved Jacobi's theorem and the following: Form the
sum Pnh of the multiplicative combinations with repetitions of the hth class
of any n numbers less than the prime p, and the sum of the combinations
without repetitions out of the remaining p—n — 1 numbers <p; then the
sum or the difference of the two is divisible by p according as h is odd or even.

Let Cl denote the sum of the combinations with repetitions of the hth
class oi 1, 2,. . ., k; Al the sum without repetitions. If 0<h<p — l,

Ci^O (mod p), j = p-k,.. ., p-2; Cl+,^Cl

For h = p-l, Ci;ik=n+1 for k = l,..., p. For h = m{p-l)+t, Cl=Ci
when k<p+l. For l<h<k, the sum of Cl and A^ is divisible by
A;^(fc+1)^; likewise, each C and A if /i is odd. For h<2k, Cl—Al is divisible
by 2A:H-1. The sum of the 2nth powers of 1, . . . , /c is divisible by 2k-\-l.

K. HenseP'^ has given the further generalization: If ai, . . . , a,^, 61, . . . , 6,
are n-\-v = p — l integers congruent modulo p to 1, 2, . . . , p — 1 in some order,
and

^l/{x) = (x-b,)... (rr-6J =x'-B,x'-'+ . . .=^B„

then, for any j, Pnj^i — iy'Bj^ (mod p), where jo is the least residue of j
mod p — 1 and Bh = 0 {k>v).

For Steiner's Z„, Z„^(a;)=a:^-i-l (mod p). Multiply (1) by
a:"(x^-^-l). Thus

X''rP{x)^X'-'+PnlX^-'+ . . .+Pnp-2X + Pnp-l-l + ^"^~^"^

X

+^"^^^"^"'+... (modp).

X

Replace \f/{x) by its initial expression and compare coefficients. Hence

p^j^i-iyBj{j=i,...,v).

Taking v=j = p — 2 and choosing 2,..., p — 1 for 61,..., 6„ we get
1= — (p — 1)! (mod p).

Converse of Fermat's Theorem.

In a Chinese manuscript dating from the time of Confucius it is stated
erroneously that 2""^ — 1 is not divisible by n if n is not prime (Jeans^^^).

Leibniz in September 1680 and December 1681 (Mahnke,^ 49-51) stated
incorrectly that 2'*— 2 is not divisible by n if n is not a prime. If n = rs,
where r is the least prime factor of n, the binomial coefficient (") was shown
to be not divisible by n, since n — 1,..., n— r+1 are not divisible by r,
whence not all the separate terms in the expansion of (1 + 1)" — 2 are

^o^Ueber die Theilbarkeit der Combinationssummen aus den natiirlichen Zahlen durch Prim-

zahlen, Progr., Bremen, 1864, 20 pp.
^"Archiv Math. Phys., (3), 1, 1901, 319; Kronecker's Zahlentheorie 1, 1901, 503.

92 History of the Theory of Numbers. [Chap, hi

divisible by n. From this fact Leibniz concluded erroneously that the
expression itself is not divisible by n.

Chr. Goldbach^^° stated that {a-\-by — a^ — b^ is divisible by p also when
p is any composite number. Euler (p. 124) points out the error by noting
that 2^^ — 2 is divisible by neither 5 nor 7.

In 1769 J. H. Lambert^'* (p. 112) proved that, if ^"•-l is divisible by a,
and d" — 1 by 6, where a, b are relatively prime, then d' — l is divisible by
ab if c is the 1. c. m. of m, n (since divisible by d"* — 1 and hence by a) . This
was used to prove that if g is odd [and prime to 5] and if the decimal fraction
for l/g has a period oi g — 1 terms, then ^ is a prime. For, if ^ = a6 [where
a, b are relatively prime integers > 1], 1/a has a period of m terms, m^a — \,
and 1/6 a period of n terms, n^b — l, so that the number of terms in the
period for 1/^ is ^ (a — 1)(6 — 1)/2<(7 — 1. Thus Lambert knew at least
the case /c = 10 of the converse of Fermat's theorem (Lucas^"' ^^').

An anonymous writer ^^^ stated that 2n+l is or is not a prime according
as one of the numbers 2"=*= 1 is or is not divisible by n. F. Sarrus^^^ noted
the falsity of this assertion since 2^'^° — 1 is divisible by the composite num-
ber 341.

In 1830 an anonymous writer^ noted that a"~^ — 1 may be divisible by n
when n is composite. In a^~^ = /cp+1, where p is a prime, set k = \q. Then
^(P-i)«=l (jjjojj pqy Ti^us oP«-i = l if a«-i = l (mod pq), and the last will
hold if g — 1 is a multiple of p — 1 ; for example, ifp = ll,g' = 31,a = 2, whence
2340=1 (mod 341).

V. Bouniakowsky^^3 proved that if A^ is a product of two primes and if
iV— 1 is divisible by the least positive integer a for which 2"=1, whence
2^~^=1 (mod N), then each of the two primes decreased by unity is divisible
by a. He noted that 3^=1 (mod 91 = 7-13).

E. Lucas^^^ noted that 2''~^=1 (mod n) for 71 = 37-73 and stated the true
converse to Fermat's theorem: If a"" — ! is divisible by p for x = p — l, but
not for x<p — lf then p is a prime.

F. Proth^^* stated that, when a is prime to n, n is a prime if a*= 1 (mod n)
for a:= (n — 1)/2, but for no other divisor of (n — 1)/2; also, if a''=l (mod n)
for x = n — l, but for no divisor <\/n of n — 1. If 71 = 7^-2*^+1, where m
is odd and < 2*", and if a is a quadratic non-residue of n, then n is a prime
if and only if a^"~^^/^= — 1 (mod n). If p is a prime >^\/n, n = mp+l is a
prime if a"~^ — 1 is divisible by n, but a^'^l is not.

*F. Thaarup^^' showed how to use a"~^=l (mod ti) to tell if n is prime.
E. Lucas^^^ proved the converse of Fermat's theorem: If a^=l (mod ti)
for a: = 71 — 1, but not for x a proper divisor oi n — 1, then n is a prime.

""Corresp. Math. Phys. (ed. Fuss), I, 1843, 122, letter to Euler, Apr. 12, 1742.

"'Annales de Math. (ed. Gergonne), 9, 1818-9, 320.

^"Ibid., 10, 1819-20, 184-7.

"»M6m. Ac. Sc. St. P6tersbourg (math.), (6), 2, 1841 (1839), 447-69; extract in Bulletin, 6, 97-8.

"*Assoc. frang. avanc. sc, 5, 1876, 61; 6, 1877, 161-2; Amer. Jour. Math., 1, 1878, 302.

"'Comptes Rendus Paris, 87, 1878, 926.

"•Nyt Tidsskr. for Mat., 2A, 1891, 49-52.

*"Th6orie des nombres, 1891, 423, 441.

Chap. Ill] CONVERSE OF FeRMAt's THEOREM. 93

G. Levi^^* was of the erroneous opinion that P is prime or composite
according as it is or is not a divisor of 10^"^ — 1 [criticized by Cipolla,^^^
p. 142].

K. Zsigmondy^^^ noted that, if g is a prime =1 or 3 (mod 4), then 2q+l
is a prime if and only if it divides (2*+l)/3 or 2^ — 1, respectively; 4g+l is
a prime if and only if it divides (2^*+l)/5.

E. B. Escott^^^ noted that Lucas'^^^ condition is sufficient but not
necessary.

J, H. Jeans^^® noted that if p, q are distinct primes such that 2^=2
(mod g), 2^=2 (mod p), then 2^^ =2 (mod pq), and found this to be the case
for pg = 11-31, 19-73, 17-257, 31-151, 31-331. He ascribed to Kossett the
result 2"-^=l (mod n) for n = 645.

A. Korselt^^^ noted this case 645 and stated that a^=a (mod p) if and
only if p has no square factor and p — 1 is divisible by the 1. c. m. of pi — 1, . . . ,
p„ — 1, where pi, . . ., p„ are the prime factors of p.

J. FraneP^^ noted that 2^^ =2 (mod pq), where p, q are distinct primes,
requires that p — 1 and g — 1 be divisible by the least integer a for which
2''=1 (mod pq). [Cf. Bouniakowsky.^^^]

L. Gegenbauer222« noted that 2^''-^=l (mod pq) if p = 2'-l = /cpr+l
and q = KT-\-l are primes, as for p = Sl, q = ll.

T. Hayashi^^^ noted that 2''— 2 is divisible by n = 11-31. If odd primes
p and q can be found such that 2^=2, 2^=2 (mod pq), then 2^'— 2 is divisible
by pq. This is the case if p — 1 and q — 1 have a common factor p' for which
2"''=! (mod pq), as for p = 23, g = 89, p' = ll.

Ph. Jolivald224 asked whether 2^-^=1 (mod N) if N = 2''-l and p is a
prime, noting that this is true if p = ll, whence iV = 2047, not a prime.
E. Malo^^^ proved this as follows:

AT-l =2(2^-1-1) =2pw, 2^-^ = (2^)2- = (Ar+l)2-=i (modiV).

G. Ricalde^^^ noted that a similar proof gives a^~''+^=l (mod N) if
N = a^—1, and a is not divisible by the prime p.

H. S. Vandiver^^^ proved the conditions of J. FraneP^^ and noted that
they are not satisfied if a< 10. Solutions for a = 10 and a = 11 are ^3 = 11-31
and 23-89, respectively.

H. Schapira^^^ noted that the test for the primality of N that a^=l

»8Monat8hefte Math. Phys., 4, 1893, 79.

*i«L'mtenn4diaire des math., 4, 1897, 270.

220Messenger Math., 27, 1897-8, 174.

''"L'interm^diaire des math., 6, 1899, 143.

^Ibid., p. 142.

=«""Monatshefte Math. Phys., 10, 1899, 373.

'^'Jour. of the Physics School in Tokio, 9, 1900, 143-4. Reprinted in Abhand. Geschichte Math.

Wiss., 28, 1910, 25-26.
*"L'interm4diaire des math., 9, 1902, 258.
^lUd., 10, 1903, 88.
*^Ibid., p. 186.

*"Amer. Math. Monthly, 9, 1902, 34-36.
»»Tchebychef's Theorie der Congruenzen, ed. 2, 1902, 306.

94

History of the Theory of Numbers.

[Chap. Ill

(mod N) ioT q = N—l, but for no smaller q, is practical only if it be known
that a small number a is a primitive root of N.

G. Arnoux--^" gave numerical instances of the converse of Fermat's
theorem.

M. Cipolla^^^ stated that the theorem of Lucas^^' impUes that, if p is
a prime and A: = 2, 4, 6, or 10, then kp-\-l is a prime if and only if 2^'^=1
(mod kp-\-l). He treated at length the problem to find a for which a^~^ = 1
(mod P), given a composite P; and the problem to find P, given a. In
particular, we may take P to be any odd factor of (a^" — l)/(a^ — 1) if p
is an odd prime not dividing a^ — 1. Again, 2^~^= 1 (mod P) for P = F^F^ ■ . .
F„ m>n> . . .>s, if and only if 2'>m, where P, = 2^''4-l is a prime. If
p and q = 2p — \ are primes and a is any quadratic residue of q, then a^«~^ = 1
(mod pq) ; we may take a = 3 if p = 4n+3 ; a = 2\i p = 4n+ 1 ; both a = 2 and
a = 3if p = 12A:+l;etc.

E. B. Escott^^° noted that e"~^ = l (mod n) if e'' — 1 contains two or more
primes whose product n is =1 (mod a), and gave a list of 54 such n's.

A. Cunningham^^^ noted the solutions n = FsF^F^QF7, n = F^. . .P15, etc.
[cf. CipoUa], and stated that there exist solutions in which n has more than
12 prime factors. One with 12 factors is here given by Escott.

T. Banachiewicz^^^ verified that 2^—2 is divisible by N for N composite
and < 2000 only when N is

341 = 11-31, 561=3-1M7, 1387 = 19-73, 1729 = 7-13-19, 1905 = 3-5-127.

Since 2^—2 is evidently divisible by N for every N = Fk = 2^ +1, perhaps
Fermat was thus led to his false conjecture that every Fk is a prime.

R. D. CarmichaeP^^ proved that there are composite values of n (a
product of three or more distinct odd primes) for which e"~^=l (mod n)
holds for every e prime to n.

J. C. Morehead^^ and A. E. Western proved the converse of Fermat's
theorem.

D. Mahnke^ (pp. 51-2) discussed Leibniz' converse of Fermat's theorem
in the form that n is a prime if a:"~^=l (mod n) for all integers x prime to n
and noted that this is false when n is the square or higher power of a prime
or the product of two distinct primes, but is true for certain products of
three or more primes, as 3-11-17, 5-13-17, 5-17-29, 5-29-73, 7-13-19.

R. D. CarmichaeP^^ used the result of Lucas^^" to prove that a^~^ = l
(mod P) holds for every a prime to P if and only if P — 1 is divisible by
X(P). The latter condition requires that, if P is composite, it be a product
of three or more distinct odd primes. There are found 14 products P of

«8« Assoc, frang., 32, 1903, II, 113-4.

"•Annali di Mat., (3), 9, 1903-4, 138-160.

""Messenger Math., 36, 1907, 175-6; French transl., Sphinx-Oedipe, 1907-8, 146-8.

"'Math. Quest. Educat. Times, (2), 1^, 1908, 22-23; 6, 1904, 26-7,55-6.

»«Spraw. Tow. Nauk, Warsaw, 2, 1909, 7-10.

"'Bull. Amer. Math. Soc, 16, 1909-10, 237-8.

^Ibid., p. 2.

"»Amer. Math. Monthly, 19, 1912, 22-7.

Chap. Ill] SYMMETRIC FUNCTIONS MoDULO p. 95

three primes, as well as P = 13-37-73457, for each of which the congruence
holds for every a prime to P.

Welsch^se stated that ifk = 4n-\-l is composite and < 1000, 2^-^ = 1 (mod
k) only for A; = 561 and 645; hence 71**= 1 (mod k) for these two k's.

P. Bachmann^^^ proved that x^'^~^'= 1 (mod pq) is never satisfied by all
integers prime to pq if p and q are distinct odd primes [Carmichael^^^].

Symmetric Functions of 1, 2,. . .p— 1 Modulo p.

Report has been made above of the work on this topic by Lagrange, ^^
Lionnet," Tchebychef,^^ Sylvester,'^^ ottmger,^^ Lucas,!"^ Cahen,!^^ Aubry,^"
Arevalo,^^^ Schuh,^^^ Frattini,!^^ steiner,^^^ Jacobi,^^! Hensel.^o^

We shall denote l"+2"+ . . . +(p — I)'* by s^, and take p to be a prime.

E. Waring^^° wrote a, j3, . . .for 1, 2, . . . , x, and considered

s = a^^^y' . . . ^a^^^y' . . . +a"/3^7'' ....

If < = a+6+c+ . . .is odd and <a:, andx+1 is prime, s is divisible by (x+l)^.
If t<2x and a, 6, . . .are all even and prime to 2a; +1, s is divisible by 2a;-f 1.

V. Bouniakowsky^^^ noted that s^ is divisible by p^, if p> 2 and m is odd
and not =1 (mod p — 1); also if both w=l (mod p — 1) and m=0 (mod p).

C. von Staudt252 proved that, if S,Xx) = 1+2"+ • • • +a;%

S^{ah)=bSM+naSn-iia)Si{b-l) (mod a"),
2S2n+i{a)^{2n+l)aS2M (mod a^).

If a,h,. . ., I are relatively prime in pairs,

S,Xah...l) SM S^il)

ah. . .1 a ' ' ' I

= integer.

A. Cauchy253 proved that 1 + 1/2+ . . . +l/(p-l)=0 (mod p).
G. Eisenstein^^^ noted that s^= — 1 or 0 (mod p) according as m is or
is not divisible by p — 1. If w, n are positive integers <p — 1,

'iyia+iy^O or - (p_f_ J' (mod p),

according as m+n<or^p — 1.

L. Poinsot^^^ noted that, when a takes the values 1, . . . , p — 1, then (ax)"
has the same residues modulo p as a", order apart. By addition, SnX'*=Sn
(mod p). Take x to be one of the numbers not a root of a;"=l. Hence
s„=0 (mod p) if n is not divisible by p — 1.

^''L'mtermMiaire des math., 20, 1913, 94.

*»'Archiv Math. Phys., (3), 21, 1913, 185-7.

""Meditationes algebraicae, ed. 3, 1782, 382.

">BuIl. Ac. Sc. St. P^tersbourg, 4, 1838, 65-9.

"'Jour, fiir Math., 21, 1840, 372-4.

"'M^m. Ac. Sc. de I'lnstitut de France, 17, 1840, 340-1, footnote; Oeuvres, (1), 3, 81-2.

«"Jour. fiir Math., 27, 1844, 292-3; 28, 1844, 232.

»"Jour. de Math., 10, 1845, 33-4.

96 History of the Theory of Numbers. [Chap, hi

J. A. Serret^^^ concluded by applying Newton's identities to (x— 1) . . .
(x— p+l)=0 that Sn=0 (mod p) unless n is divisible by p — 1.
J. Wolstenholme^" proved that the numerators of

1+UU...+ 1 1+1 + . ■ 1

2 ' 3 ' •■• ' p-r - . 22 ' ••• ' (p-l)2

are divisible by p^ and p respectively, if p is a prime >3. Proofs have also
been given by C. Leudesdorf^^s, A. Rieke,^^^ E. Allardice,^^" G. Osborn,^"
L. Birkenmajer,^" P. Niewenglowski,^^ N. Nielsen,^" H. Valentiner,^®^
and others.^^^

V. A. Lebesgue^®' proved that s^ is divisible by p if w is not divisible
by p — 1 by use of the identities

(n+1) S k{k+l) . . .ik-\-n-l)=xix+l) . . .(x+n) (n = l,. . ., p-1).

k=l

P. Frost^^^ proved that, if p is a prime not dividing 2^'' — 1, the numera-
tors of a2r, (T2r-i, p(2r — l)o-2r+2(T2r-i are divisible by p, p^, p^, respectively,
where

1J_1_L 1

2* ' •" ' (p-1)'

The numerator of the sum of the first half of the terms of 0*2, is divisible by
p; likewise that of the sum of the odd terms.

J. J. Sylvester^^^ stated that the sum S^, m of all products of n distinct
numbers chosen from 1,. . ., m is the coefficient of T in the expansion of
{l+t){l-\-2t) . . . (1+wO and is divisible by each prime >n+l contained in
any term of the set m— n+l,. . ., m, m+1.

E. Fergola"" stated that, if (a, 6, . . . , ly represents the expression
obtained from the expansion of (a+6H- . . . +0" by replacing each numerical
coefficient by unity, then

(X, x+1,. . ., x+rr= i CY)^^' 2,. . ., rr-^x^.

*"Coiirs d'algSbre sup^rieure, ed. 2, 1854, 324.

«'Quar. Jour. Math., 5, 1862, 35-39.

"sProc. London Math. Soc, 20, 1889, 207.

«»Zeit8chrift Math. Phys., 34, 1889, 190-1.

««oProc. Edinburgh Math. Soc, 8, 1890, 16-19.

"'Messenger Math., 22, 1892-3, 51-2; 23, 1893-4, 58.

"^Prace Mat. Fiz., Warsaw, 7, 1896, 12-14 (Polish).

M'Nouv. Ann. Math., (4), 5, 1905, 103.

««Nyt Tidsskrift for Mat., 21, B, 1909-10, 8-10.

^Ibid., p. 36-7.

^^Math. Quest, Educat. Times, 48, 1888, 115; (2), 22, 1912, 99; Amer. Math. Monthly, 22, 1915,

103, 138, 170.
«^Introd. k la thdorie des nombres, 1862, 79-80, 17.
»8Quar. Jour. Math., 7, 1866, 370-2.
M»Giomale di Mat., 4, 1866, 344. Proof by Sharp, Math. Ques. Educ. Times, 47, 1887, 145-6;

63, 1895, 38.
"oibid., 318-9. Cf. Wronski"! of Ch. VIII.

Chap. Ill]

Symmetric Functions Modulo p.

97

The number (1, 2, . . ., r)'* is divisible by every prime >r which occurs in
the series n+2, n+3, . . ., n+r.
G. ToreUi"! proved that

(ai, . . . , GnY = (ai, . . . , a„_iy+a„{ai, . . . , a^y~\
(fli,. . ., o„, ^y-Cfli,. . ., fln, c)'"=(6-c)(ai,. . ., a„, 6, cy-\

which becomes Fergola's for ai = i (i = 0, . . ., n). Proof is given of Syl-
vester's^^^ theorem and the generahzation that >Sy,i is divisible by (}+!).

Torelli^^^ proved that the sum o-„, « of all products of n equal or distinct
numbers chosen from 1, 2, . . ., m is divisible by (n+T), and gave recursion
formulas for o-n, m-

C. Sardi^'^^ deduced Sylvester's theorem from the equations Ai — (|),, . .
used by Lagrange. ^^ Solving them for Ap = Sp,n, we get

pi{-iy^%,,=

-1

G)

(a)
C)

0
-2

i;--i)

0

V 2 ;

0

\ 3 ;

0

("to

(

n-p+2\ /n+1
2 y Vp+^

D

If n+l is a prime we see by the last column that >S„_i.„ is divisible by n+1.
When p = n — l, denote the determinant by D. Then if n+l is a prime,
D is evidently divisible by n+l. Conversely, if D is divisible by n+l and
the quotient by (n — 1) !, then n+l is a prime. It is shown that

p=l

r„ = F+...+n^

Using this for m = 1, . . . , n, we see that Vp is divisible by any integer prime
to 2, 3, . . ., p+1 which occurs in n+l or n. Hence if n+l is a prime, it
divides ri, . . ., r„_i, while rn=n (mod n+l). If n+l divides r„_i it is a
prime.

Sardi"^ proved Sylvester's theorem and the formula

S ( — l)''>Si,, n+r-lO'k-r, n+r = 0,
r-0

stated by Fergola."^

"iQiornale di Mat., 5, 1867, 110-120.
"276id., 250-3.
"mid., 371-6.
"*Ibid., 169-174.
"Ubid., 4, 1866, 380.

98 History of the Theory of Numbers. [Chap, hi

Sylvester"^ stated that, if pi, p2, . . .are the successive primes 2, 3, 5, . . .,

^'^^ ^T^^A^ ^'-'^''^'

where Fk{n) is a polynomial of degree k with integral coefficients, and the
exponent e of the prime p is given by

E. Ces^ro^" stated Sylvester's^®^ theorem and remarked that <S„.„— n!
is divisible by w —n if m—n is a prime.

E. Ces^ro"^ stated that the prime p divides /S^.p-2 — 1, *Sp_i.p+l, and,
except when m = p — l, S^.p-i- Also (p. 401), each prime p>{n+l)/2
divides *Sp_i.„H-l, while a prime p = (n+l)/2 or n/2 divides »Sp_i.„+2.

O. H. Mitchell"^ discussed the residues modulo k (any integer) of the
symmetric functions of 0, 1, . . . , /c — 1. To this end he evaluated the residue
of (x— a)(x— /3) . . ., where a, /3, . . .are the s-totitives of k (numbers<A: which
contain s but no prime factor of k not found in s) . The results are extended
to the case of moduli p, f{x), where p is a prime [see Ch. VIII].

F. J. E. Lionnet^^° stated and Moret-Blanc proved that, if p = 2n+l is
a prime> 3, the sum of the powers with exponent 2a (between zero and 2n)
of 1, 2, . . . , n, and the like sum for n-\-l, n+2, . . . , 2n, are divisible by p.

M. d'Ocagne^^^ proved the first relation of Torelli.^^^

E. Catalan^^^ stated and later proved^^^ that s^ is divisible by the prime
p>k-\-l. If p is an odd prime and p — 1 does not divide k, Sk is divisible
by p; while if p — 1 divides k, Sk= — l (mod p). Let p = a''b^ . . . ; if no one
of a — 1, 6 — 1,. . . divides k, Sk is divisible by p; in the contrary case, not
divisible. If p is a prime >2, and p — 1 is not a divisor of k-\-l, then

^ = l^(p-l)'+2*(p-2)^+ . . .+{p-iyv

is divisible by p; but, if p — 1 divides k+l, S= — { — iy (mod p). If k and I
are of contrary parity, p divides S.

M. d'Ocagne^^ proved for Fergola's^'^" symbol the relation

(a. . .fg. . .1. . .V. . .zr^Xia. . .frig. . .^)^ ..{v. . .z)",

summed for all combinations such that X+/i+. . .-\-p = n. Denoting by
a^^^ the letter a taken p times, we have

i=0

"«Nouv. Ann. Math., (2), 6, 1867, 48.

»"Nouv. Correap. Math., 4, 1878, 401; Nouv. Ann. Math., (3), 2, 1883, 240.

"8Nouv. Coiresp. Math., 4, 1878, 368.

"»Amer. Jour. Math., 4, 1881, 25-38.

"ONouv. Ann. Math., (3), 2, 1883, 384; 3, 1884, 395-6.

"»/6id., (3), 2, 1883, 220-6. Cf. Ces^ro, (3), 4, 1885, 67-9.

2«BuU. Ac. Sc. Belgique, (3), 7, 1884, 448-9.

"'M6m. Ac. R. Sc. Belgique, 46, 1886, No. 1, 16 pp.

»**Nouv. Ann. Math., (3), 5, 1886, 257-272.

Chap. Ill] SYMMETRIC FUNCTIONS MODULO p. 99

It is shown that (1^^^)" equals the number of combinations of n-\-p — l
things p — 1 at a time. Various algebraic relations between binomial
coefficients are derived.

L. Gegenbauer^^^ considered the polynomial

p-2+k

f{x)= S hix' {l-p<k^p-l)

i=0

and proved that

V/(X)/X^-2= -h,.2 (mod p), k<p-l,

X=l

'xf{X)/\^-'= -6p_2-fc2p-3 (mod p), k = p-\,

X=l

and deduced the theorem on the divisibility of s„ by p.

E. Lucas^^^ proved the theorem on the divisibility of s„ by p by use of the
symbolic expression (s+l)"— s" for x" — 1.

N. Nielsen^^^" proved that if p is an odd prime and if k is odd and
\<k<p — \, the sum of the products of 1, . . ., p — 1 taken A; at a time is
divisible by p^. For k=p—2 this result is due to Wolstenholme.^^^

N. M. Ferrers^^^ proved that, if 2n+l is a prime, the sum of the products
of 1, 2, . . . , 2n taken r at a time is divisible by 2n+l if r<2n [Lagrange^^],
while the sum of the products of the squares of 1, . . . , n taken r at a time is
divisible by 2n+l if r<n. [Other proofs by Glaisher.^^^]

J. Perott^^^ gave a new proof that s^ is divisible by p if n<p — l.

R. Rawson^^^ proved the second theorem of Ferrers.

G. Osborn^^° proved for r<p — l that s^. is divisible by p if r is even, by
p^ if r is odd; while the sum of the products of 1, . . ., p — l taken r at a
time is divisible by p^ if r is odd and l<r<p.

J. W. L. Glaisher^^^ stated theorems on the sum Sriai,..., a,) of the
products of fli, . . . , rti taken r at a time. If r is odd, Sr{l, . . . , n) is divisible
by n+1 (special case n+1 a prime proved by Lagrange and Ferrers). If r
is odd and > 1, and if n+1 is a prime> 3, Sr{l, . . . , n) is divisible by {n-{-iy
[Nielsen^^^'']. If r is odd and >1, and if w is a prime >2, Sril,. . ., n) is
divisible by n^. If n+1 is a prime, Sr{l^,. • ■, n^) is divisible by n+1 for
r = l,...,n — 1, except for r = n/2, when it is congruent to ( — 1)1+"/^ j^odulo
n+1. If p is a prime ^n, and k is the quotient obtained on dividing n+1
by p, then aSp_i(1,..., n)=— A; (mod p); the case n = p — 1 is Wilson's
theorem.

"^Sitzungsber. Ak. Wiss. Wien (Math.), 95 II, 1887, 616-7.

"«Th6orie des nombres, 1891, 437.

286aNyt Tidsskrift for Mat., 4, B, 1893, 1-10.

"'Messenger Math., 23, 1893-4, 56-58.

288BuU. des sc. math., 18, I, 1894, 64. Other proofs. Math. Quest. Educ. Times, 58, 1893, 109;

4, 1903, 42.
"•Messenger Math., 24, 1894-5, 68-69.
""Ibid., 25, 1895-6, 68-69.
"'Ibid., 28, 1898-9, 184-6. Proofs"*.

100

History of the Theory of Numbers.

[Chap. Ill

S. Monteiro'^- noted that 2n+l divides {2n)\Z\n/r.

J. Westlund-^^ reproduced the discussion by Serret^^^ and Tchebychef.'^^

Glaisher^^ proved his^^^ earlier theorems. Also, ii p = 27n+l is prime,

{m-t)pS2t{l,.. ., 2m)=S2t+i{l,. ■ ., 2m) (mod f)

and, if i>l, modulo p'^. According as n is odd or even,

>S2t(l,. . ., n)=S2t{l,. . ., n-1) (mod n^ or ^n^).

For m odd and >3, S2m-z0-i- . ., 2m — 1) is divisible by m^, and

^„_2(1^..., \m-l\^), ^2n.-4(l,...,2m-l)

are divisible by m. He gave the values of Sr{\,. ■ ■, n) and Ar = Sr{l,. . .,
n — 1) in terms of n for r = l,. . ., 7; the numerical values of 5^(1,. . ., n)
for n^22, and a list of known theorems on the divisors of Ar and Sr. For
r odd, 3^r^m — 2, Sr{l, . . ., 2w— 1) is divisible by m and, if w is a prime
>3, by m.^ He proved {ibid., p. 321) that, if l^r^ (p-3)/2, and 5, is a
BernoulU number,

2.S2.+i(l,. . ., p-l)_-{2r+l)S2r{l,..., p-1)

V V

^2.(i,...,p-i)_(-ir5:

V

2t

(modp).

Glaisher^^^ gave the residues of a^ [Frost^^^] modulo p^ and p^ and proved
that (72, o'i, •• . , o-p-3 are divisible by p, and 0-3, cs, . . . , o-p_2 by p^, if p is
a prime.

Glaisher^^® proved that, if p is an odd prime.

■'•"' o2n I r2n I '

(p-2)

2n

^0 or — I (mod p),

according as 2n is not or is a multiple of p — 1. He obtained (pp. 154-162)
the residue of the sum of the inverses of like powers of numbers in arith-
metical progression.

F. Sibirani^^^" proved for the Sn,m of Sylvester^^^ (designated Sn,m-\-\) that

^n,n '^n— l,n • • • *^n— Jfe+l.n

On+A;— l,n+*— 1 Sn+k—2,n+k—l ■ ■ ■ ^n.n+k—l

t

= inl)K

"'Jornal Sc. Mat. Phys. e Nat., Lisbon, 5, 1898, 224.
»»Proc. Indiana Ac. Sc, 1900, 103-4,
"^Quar. Jour. Math., 31, 1900, 1-35.
»'/Wd., 329-39; 32, 1901, 271-305.
"•Messenger Math., 30, 1900-1, 26-31.
'wPeriodico di Mat., 16, 1900-1, 279-284.

Chap. Ill] SyMMETKIC FUNCTIONS MODULO p. 101

K. HenseP^^ proved by the method of Poinsot^^^ that any integral sym-
metric function of degree v of 1,..., p — 1 with integral coefficients is
divisible by the prime p if y is not a multiple of p — 1.

W. F. Meyer^^^ gave the generalization that, if ai, . . . , ap_i are incongru-
ent modulo p", and each af~^ — 1 is divisible by p", any integral symmetric
function of degree voiai,..., ap_i is divisible by p'* if v is not a multiple of
p — 1. Of the </)(p") residues modulo p", prime to p, there are p'^Cp — 1)^ for
which a^~^ — l is divisible by p"~^~'^, but by no higher power of p, where
A; = 1, . . ., n— 1; the remaining p — 1 residues give the above ai,..., a^-i.

J. W. Nicholson^^^ noted that, if p is a prime, the sum of the nth powers
of p numbers in arithmetical progression is divisible by p if n<p — 1, and
= — 1 (mod p) if 71 = p — 1.

G. Wertheim^"'' proved the same result by use of a primitive root.

A. Aubry^°^ took x = 1, 2, . . . , p — 1 in

(a:+l)"-rc" = nx^-i+Ax"-2+ . . . -{-Lx+l
and added the results. Thus

p'' = ns„_i+As„_2+. . .+Lsi+p.

Hence by induction Sn_i is divisible by the prime p if n<p. He attributed
this theorem to Gauss and Libri without references.

U. Concina^°^ proved that s„ is divisible by the prime p>2 if n is not
divisible by p — 1. Let 5 be the g. c. d. of n, p — 1, and set ^i5 = p — 1. The
)u distinct residues Ti of nth powers modulo p are the roots of ^"=1 (mod p),
whence Sr,=0 (mod p) for n not divisible by p — 1. For each r^-, x'*=rj has
6 incongruent roots. Hence s„=5Sri=0. He proved also that, if p+1 is
a prime >3, and n is even and not divisible by p, l''+2''+ . . . +(p/2)'* is
divisible by p+1.

W. H. L. Janssen van Raay^°^ considered, for a prime p>3,

(p-1)! ^ (P-I)I

^''~ h ' ^'~h{v-h)

and proved that B^-\-B2-\- . . . +-B(p_i)/2 is divisible by p, and

are divisible by p^.

U. Concina^o^ proved that ^ = 1+2"+ . . .+/c" is divisible by the odd
number A; if n is not divisible by p — 1 for any prime divisor of p of k. Next,
let k be even. For n odd > 1, ^ is divisible by k or only by k/2 according

"'Archiv Math. Phys., (3), 1, 1901, 319. Inserted by Hensel in Kronecker's Vorlesungen tiber

Zahlentheorie I, 1901, 104-5, 504.
"sArchiv Math. Phys., (3), 2, 1902, 141. Cf. Meissner'" of Ch. IV.
"^Amer. Math. Monthly, 9, 1902, 212-3. Stated, 1, 1894, 188.
^ooAnfangsgninde der Zahlentheorie, 1902, 265-6.
'"iL'enseignement math., 9, 1907, 296.
»°2Periodico di Mat., 27, 1912, 79-83.
"'Nieuw Archief voor Wiskunde, (2), 10, 1912, 172-7.
so^Periodico di Mat., 28, 1913, 164-177, 267-270.

102 History of the Theory of Numbers. [Chap. hi

as k is or is not divisible by 4. For n even, S is divisible only by k/2 pro-
vided n is not divisible by any prime factor, diminished by unity, of k.

N. Nielsen^"^ wrote Cp for the sum of the products r at a time of 1, ... ,
p — 1, and

s„(p)=2;s^ (7„(p)=S(-l)''-V.
*-l «=1

If p is a prime >2m+1,

o-2n(p-l)=S2n(p-l)=0(modp), Sgn+iCp " 1) = O(niod p2).

If p = 2n+l is a prime >3, and l^r^n — 1, Cf'^^ is divisible by p^.

Nielsen^''^ proved that 2Di^'^^ is divisible by 2n for 2p+l^n, where D\
is the sum of the products of 1, 3, 5, . . . , 2n — 1 taken s at a time; also,

2^"+'s2fl(n - 1) = 2^%,{2n - 1) (mod 4n^),

and analogous congruences between sums of powers of successive even or
successive odd integers, also when alternate terms are negative. He proved
(pp. 258-260) relations between the C's, including the final formulas by
Glaisher.29^

Nielsen^°^ proved the results last cited. Let p be an odd prime. If
2n is not divisible by p — 1, S2r.(p — 1) = 0 (mod p), S2„+i(p — 1)=0 (modp^).
But if 2n is divisible by p — 1,

S2n(p-1)=-1, S2„+i(p-l) = 0 (modp), Sp(p - 1) = 0 (mod p^).

T. E. Mason^"^ proved that, if p is an odd prime and i an odd integer > 1,
the sum Ai of the products i at a time of 1, . . . , p — 1 is divisible by p^. If
p is a prime >3, Sk is divisible by p^ when k is odd and not of the form
m(p — 1) + 1, by p when k is even and not of the form 7n{p — l), and not
by p if A: is of the latter form. If A; = 7n(p — 1) + 1, s^ is divisible by p^ or
p according as k is or is not divisible by p. Let p be composite and r its
least prime factor; then r — 1 is the least integer t for which At is not divisible
by p and conversely. Hence p is a prime if and only if p — 1 is the least t for
which At is not divisible by p. The last two theorems hold also if we
replace A's by s's.

T. M. Putnam^"^ proved Glaisher's^^^ theorem that s_„ is divisible by
p if n is not a multiple of p — 1 , and

(p-l)/2 9 — 9P

2 jp-2=f_A(inodp).
y-i p

W. Meissner^^° arranged the residues modulo p, a prime, of the successive

•o'K. Danske Vidensk. Selsk. Skrifter, (7), 10, 1913, 353.

"•Annali di Mat., (3), 22, 1914, 81-94.

•"Ann. sc. I'^cole norm, sup., (3), 31, 1914, 165, 196-7.

"*T6hoku Math. Jour., 5, 1914, 136-141.

»"Amer. Math. Monthly, 21, 1914, 220-2.

"•Mitt. Math. Gesell. Hamburg, 5, 1915, 159-182.

1

i

1

2

4

8

3

6

12

11

9

5

10

7

Chap. Ill] SYMMETRIC FUNCTIONS MODULO Jp. 103

powers of a primitive root /i of p in a rectangular table of t rows and r col-
umns, where ir = p — 1. For p = 13, /i = 2, i = 4, the table
is shown here. Let R range over the numbers in any
column. Then Si2 and Sl/^R are divisible by p. If Ms
even, Sl/i? is divisible by p^ as 1/1 + 1/8+1/12+1/5 =
13^/120. For t = p — \, the theorem becomes the first one
due to Wolstenholme.^^^ Generalizations are given at the end of the
paper.

N. Nielsen^^^ proved his^^^*" theorem and the final results of Glaisher.^^^
Nielsen^^^ proceeded as had Aubry^°^ and then proved

(p-l)/2 ^_3

S2„+i^0 (mod f), S r^O (mod p), l^n^ ^ .

Then by Newton's identities we get Wilson's theorem and Nielsen's^"^ last
result.

E. Cahen^^^ stated Nielsen's^^^'' theorem.

F. Irwin stated and E. B. Escott^^* proved that if Sj is the sum of the
products J at a time of 1, 1/2, 1/3,. ., \/t, where ^= (p — 1)/2, then 2S2—Si^,
etc., are divisible by the odd prime p.

"iQversigt Danske Vidensk. Selsk. ForhandUnger, 1915, 171-180, 521.

3i276id., 1916, 194-5.

'i^Comptes Rendus Stances Soc. Math. France, 1916, 29.

»"Ainer. Math. Monthly, 24, 1917, 471-2.

I

CHAPTER IV.

RESIDUE OF (C/^->-l)/P MODULO P.
N. H. Abel^ asked if there are primes p and integers a for which

(1) a^-'=l (modp'), l<a<p.

C. G. J. Jacobi^ noted that, for p^37, (1) holds only when p = ll,
a = 3 or 9; p = 29, a = 14; p = 37, a = 18. Cf. Thibault^^ of Ch. VI.
G. Eisenstein^ noted that, for p a prime, the function

has the properties

(2) quv=qu-\-qv, qu+pv^Qu-- (mod p),

2g2=l-Ki-|+ • • • — ^^^\ Md p),

P 1 o

where s = (p+l)/2, . , ., p — 1. All solutions of (1) are included in a=
u+puqu, 0<u<p.

E. Desmarest^ noted that (1) holds for p = 4S7, a = 10, and stated that
p = 3 and p = 487 are the only primes < 1000 for which 10 is a solution.

J. J. Sylvester^ stated that, if p, r are distinct primes, p>2, then g^
is congruent modulo p to a sum of fractions with the successive denominators
p — 1, . . . , 2, 1 and (as corrected) with numerators the repeated cycle of the
positive integers ^r congruent modulo r to 1/p, 2/p,. . ., r/p. Thus, for
r = 5,

p — 1 p — 2 p — 6 p — 4: p — 0 p — 0

j,^^+.-l-+-i-+^+-^+-l-+... (p=10fc+7).

p — 1 p—2 p — S p—4: p — 5 p — 0

According as p = 4A;+l or 4A: — 1, ^2 is congruent to
2.22.2. 2

p—S p—4: p-7 p—S p — ll
2 2 2 2 2

p-2 p-3 p-Q p-7 p-10 "
[the signs were given + erroneously]. For any p,

?2= 7-\ ^ 5+... (modp).

p—1 p—2 p—o

iJour. fiir Math., 3, 1828, 212; Oeuvres, 1, 1881, 619.

mid., 301-2; Werke, 6, 238-9; Canon Arithmeticus, Berlin, 1839, Introd., xxxiv.
'BerUn Berichte, 1850, 41.
*Th6orie des nombres, 1852, 295.

'Comptes Rendus Paris, 52, 1861, 161, 212, 307, 817; Phil. Mag., 21, 1861, 136; Coll. Math.
Papers, II, 229-235, 241, 262-3.

105

106 History of the Theory of Numbers. [Chap, iv

Jean Plana^ developed j (Af — 1) + 1 } " and obtained

M''-M-\{M-iy-{M-l)\=pf{M),

Take M = m, 7n — l,. . ., 1 m the first equation and add. Thus

=/(!) + . . . 4-/(w) =Si+^^S2-f • • • +Sp-i,

where s, = r+2'H- . . . + (m — 1)'. For j> 1, we may replace p by j and get

m

-w=is,_i+ (0s,_2+ Qjsi-aH- • • • +isi,

a result obtained by Plana by a long discussion [Euler"]. He concluded
erroneously that each Si is divisible by m (for m = 3, S2 = 5).

F. Proth^ stated that, if p is a prime, 2''— 2 is not divisible by p^ [error,
see Meissner^^].

M. A. Stern^ proved that, if p is an odd prime,

rrf — m_ , , , 1 _ , i , ,1

— - — =Si-§S2+iS3-. . .-— YSp-i=o-p-i+io-p_2+. . • + —^0-1

for Si as by Plana and 0-^ = l'+2*+ • • . +w\ Proof is given of the formula
below (2) of Eisenstein^ and Sylvester's formulae for q2 (corrected), as well
as several related formulae.

L. Gegenbauer^ used Stern's congruences to prove that the coefficient of
the highest power of a^ in a polynomial f{x) of degree p — 2 is congruent to
{m^—m)/p modulo p if /(a:) satisfies one of the systems of equations

J{\) = {-lf^'V-\{m-\), /(X)=X--VxW (X = l,. . ., p-1).

E. Lucas^° proved that ^2 is a square only for p = 2, 3, 7, and stated the
result by Desmarest.^

F. Panizza^^ enumerated the combinations p at a time of ap distinct
things separated into p sets of a each, by counting for each r the combina-
tions of the things belonging to r of the p sets :

(T)=i.(^>a) CO ■•(")'

•Mem. Acad. Turin, (2), 20, 1863, 120.

^Comptes Rendus Paris, 83, 1876, 1288.

•Jour, fur Math., 100, 1887, 182-8.

•Sitzungsber. Ak. Wiss. Wien (Math.), 95, 1887, II, 616-7.
">Th6orie des nombres, 1891, 423.
"Periodico di Mat., 10, 1895, 14-16, 54-58.

Chap. IV] RESIDUE OF {U^^ — l)/^ MoDULO y. 107

where ^l^-...^-^r = p, ij>0. The term given by r = p is a^. For p a
prime, the left member is =a (mod p) and we have Fermat's theorem. By
induction on r,

Taking r = p, we have

D. Mirimanoff^^ wrote ao for the least positive integer making aop+1
divisible by the prime r<p, and denoted the quotient by r%i, where 6i is
prime to r. Similarly, let a^ be the least positive integer such that a,p+6i =
r%ij^i. We ultimately find an n for which 6n = l- Then 6„4.j = 6i. By (2),

?b<~r-^i?'-+?6.>" - .^ 7r=gr2ei(modp).

Oi »-0 Oj

Let r belong to the exponent co modulo p and set 6w = p — 1. Then Sev=co,
while 1, 61, . . . , 6„_i are the distinct residues of the eth powers of the integers
< r and prime to r. Thus

g^=eS -^ (mod p).

The formula obtained by taking r a primitive root of p is included in the
following, which holds also for any prime r :

$,= 2 -* (mod p),

ai being the least positive integer for which aip+iSi=0 (mod r). Set
/3i = p— 5, p'p=l (mod r), 0<p'<r. Then ai=p'b — \ (mod r),

]A;} being the least positive residue modulo r of k. Whence Sylvester's^
statement.

J. S. Aladow^^ proved that (1) has at most (p=f1)/4 roots if p = 4?n=tl.

A. Cunningham^^" listed 27 cases in which r^~^=l or r'=l (mod p'),
r<p^~^, where Z is a divisor of p — 1. For the 11 cases of the first kind,
p = 5, 7, 17, 19, 29, 37, 43, 71, 487.

W. Fr. Meyer^^ proved by induction that, if p is a prime, x^~^ — l is
divisible by p* {l^k<n), but not by p^'^^, for exactly p"~^~^ (p — 1)^ posi-
tive integers a:<p" and prime to p, and is divisible by p" for the remaining
p — 1 such integers. Set

^=a+MiP+. ■ ■+MnP" (l^Q<P,0^iU><p), Xp=(a^'-a"' Vp

"Jour, fiir Math., 115, 1895, 295-300.

"St. Petersburg Math. Soc. (Rusaian), 1899, 40-44.

"<»Messenger Math., 29, 1899-1900, 158. See Cuniungham"^, Ch. VI.

"Archiv Math. Phys., (3), 2, 1901, 141-6.

108 History of the Theory of Numbers. [Chap, iv

If k is the least index for which fXk^Xk, M/»=^/. (mod p) for h<k, then
A'~^ — l is divisible by p*", but not by p^"*"^.

A. Palmstrom and A. Pollak^^ proved that, if p is a prime and n, m are.
the exponents to which a belongs modulo p, p~, respectively, then a"" — !
is divisible by p^, so that m is a multiple of n and a divisor of np, whence
m = n OT pn. Thus according as a^~^ is or is not =1 (mod p^), m = n or
m = np.

Worms de Romilly^^" noted that, if co is a primitive root of p^, the incon-
gnient roots of x^^=l (mod p^) are co^^{j = l,. . ., p — 1).

J. W. L. Glaisher^^ proved that if r is a positive integer <p, p sl prime,

r''-^ = l+^iP+K^i'-^2)p'+|(^i'-3^i^2+2^3)p'+. . .,
where Qn is the sum of the nth powers of

1 _2_ r-1 . 1 2 r-1 . 1

a [2(t]'" '' [{r-l)a]' r+cr' r+[2(T]'" '' r+[(r-lV]' 2r+(r'* ' ''

a being the least positive residue modulo r of — p. If /i^ is the least positive
solution of ani=i (mod r), viz., p/i<H-i=0, then

Ml , M2 , I Mr-l , Ml , M2 I , Mr-1 , Ml ,

12 r-1 r + 1 r+2 ' ' ' ' ' 2r-l ^ 2r+l ' "

Set /Ur = Oj Mi+jr =Mi- Then

g^=i\^)\ s'^'^O(modp).

Sylvester's corrected results are proved. From (1 + 1)^,

op_2 1 / 1 \

=l-^+i- • . • 7^2(l+K . . . + -) (mod p).

p p — 1 \ p — 2/

For r' = r+A:p, let m/ be the positive root of p/x/+^=0 (mod r'). Then
It is shown that, for some integer t,

k k k^ 2k k^

hi-gi+- = tp, h2-g2= -2---2+^t-y9i-:^ (mod p),

Glaisher,^^ using the same notations, gave

^'-'-l+p(^+f +...+^l) (modp=).

"L'intermddiaire des math., 8, 1901, 122, 205-6 (7, 1900, 357).

^Ibid., 214-5.

'•Quar. Jour. Math., 32, 1901, 1-27, 240-251.

"Messenger Math., 30, 1900-1, 78.

Chap. IV] RESIDUE OF (U^ ^ — l)/p MODULO p. 109

Glaisher^^ considered Qu in connection with BernouUian numbers and
gave

^-^^-i(}+l+ +1) (modp = 3ft+l).

A. Pleskot^^ duplicated the work of Plana. ^

P. Bachmann^° gave an exposition of the work by Sylvester,^ Stern,*
Mirimanoff.-^^

M. Lerch^^ set, for any odd integer p and for u prime to p,

P

Then,* as a generahzation of (2),

qnv =qu+qv, Qu+pv =qu-\ (mod p) ,

"-I^H- 2g.-2i— 2I (mod p),

where v ranges over the positive integers <p and prime to p; X over those
>p/2; fi over those <p/2. Henceforth, let p be an odd prime and set

N=\{p-l)\+l\/p. Then N^q,+ . . .+q,.^,

[P/4]1 [p/3]i [p/5]i [2p/5U

32^-1 si, 3^3= -2 si, 5^5^-2 2^-2 Si

»=l^ v=l^ a=l« 5=1 0

modulo p. If \p(n) is the number of sets of positive solutions <p oi ixv = n
and hence the number of divisors between n/p and p of n,

Employing Legendre's symbol and BernoulHan numbers, we have
^= sY^)g =0 or (-1)"-^2j5„ (mod p),

v=l \p/

according as p = 4n+3 or 4n+l. In the respective cases,

p-i

\{^^Vq.^Cl{-p)oTO{modp),

where CZ(— A) is the number of classes of positive primitive forms
ax^+bxy+cy^ of negative discriminant 6^— 4ac= —A. Also, modulo p,

y^iv'^LpJ' ^ ^aaLpJ'

6 ao Lp J a 0 aabf-pj

where a, a are quadratic residues of p, and 6, /3 non-residues.

isProc. London Math. Soc, 33, 1900-1, 49-50.

"Zeitschrift fiir das Realschulwesen, Wien, 27, 1902, 471-2.

"Niedere Zahlentheorie, I, 1902, 159-169. *The greatest integer ^x is denoted by [x].

"Math. Annalen, 60, 1905, 471-490.

1 10 History of the Theory of Numbers. [Chap, iv

H. F. Baker" extended Sylvester's theorem to any modulus N:

A' »-l N — TTli

where the m, denote the integers <A^ and prime to A'", N'N=1 (mod r),
and \k\ is the least positive residue modulo r of k.

Lerch^ extended Mirimanofif's^^ formula to the case of a composite
modulus m. Set

m
Let a belong to the exponent <f){m)/e. Then q{a, m)=e'Za/^ (mod m),
where /? ranges over the residues of the incongruent powers of a, and
wa+j3=0 (mod a), 0^a<a. As an extension of Sylvester's theorem,

T T '

q(a, w)=2-= —2-^ (mod m),

V V

where v ranges over the integers < m and prime to m, while

7nr,-\-v=0, wr/ — ?'=0 (mod a), 0^r,<a, 0^r,'<a.

For m = mi. . .rtik, where the rrij are relatively prime,

k

q{a, m) = 2 njn/(l){nj)q{a, nij) (mod m),

where m = mjnj, n/n/=l (mod mj).

H. Hertzer-'* verified that, for a<p<307, a^^ — 1 is di\'isible by p^ only
for a = 68, p = 113; a = 3, 9, p = ll. He examined all the primes between
307 and 751, but only for a and p — a when a<y/p, finding only p = 113,
a = 68. Removing the restriction a< Vp^ be found only the solutions
p = ll,a = 3; p = 331, a = 18, 71; p = 353,a = 14;
p = 487, a = 10, 175; p = 673, a = 22,
together with the square of each a.

A. Friedmann and J. Tamarkine^^ gave formulas connecting q^ with
Bernoullian numbers and [u/p].

A. Wieferich^® proved that if x^+y^-\-z^ = Q is satisfied by integers
X, y, z prime to p, where p is an odd prime, then 2""^ = 1 (mod p^). Shorter
proofs were given by D. IMirimanoff-^ and G. Frobenius.'*

D. A. Grave- ^ gave the residue of q^ for each prime p< 1000 and thought
he could prove that 2^ — 2 is never divisible by p^ (error, Meissner^).

A. Cunningham^" verified that 2^ — 2 is not divisible by p^ for any prime
p< 1000, and^^ that 3^ - 3 is not divisible by p^ for a prime p = 2''3''+ 1< 100.

W. H. L. Janssen van Raay^^ noted that 2^ — 2 is not divisible by p^ in
general.

»Proc. London Math. Soc, (2), 4, 1906, 131-5. "Comptes Rendus Paris, 142, 1906, 35-38.
"Archiv Math. Phys., (3), 13, 1908, 107. «Jour. fur Math., 135, 1909, 146-156.

»Jour. fiir Math., 136, 1909, 293-302. "L'enseignement math., 11, 1909, 455-9.

"Sitzungsber. Ak. Wiss. Berlin, 1909, 1222-4; reprinted in Jour, fiir Math., 137, 1910, 314.
**An elementary text on the theory of numbers (in Russian), I^ev, 1909, p. 315; Kiev Izv. Univ.,

1909, Nos. 2-10.
"Report British Assoc, for 1910, 530. L'interm^diaire des math., 18, 1911, 47; 19, 1912, 159.

Proc. London Math. Soc, (2), 8, 1910, xiii.
"L'interm^diaire des math., 18, 1911, 47. Cf., 20, 1913, 206.
"Nieuw Archief voor Wiskunde, (2), 10, 1912, 172-7.

Chap. IV] RESIDUE OF {U^^ — l)/p MODULO p. Ill

' L. Bastien^^" verified that (1) holds for p< 50 only for p= 43, a= 19, and
for Jacobi's^ cases. He stated that, if p= 4p='= 1 is a prime,

-1^2=1 + 1/3+1/5+... +1/(2/1-1) (mod p).

W. Meissner^^ gave a table showing the least positive residue of (2' — l)/p
modulo p for each prime p< 2000, where t is the exponent to which 2 belongs
modulo p. In particular, 2^ — 2 is divisible by the square of the prime
p = 1093, contrary to Proth^ and Grave,^^ but for no other p<2000.

In the chapter on Fermat's last theorem will be given not only the con-
dition q2—0 (mod p) of Wieferich^^ but also q^^O (mod p), etc., with cita-
tions to D. Mirimanoff, Comptes Rendus Paris, 150, 1910, 204-6, and Jour,
fiir Math., 139, 1911, 309-324; H. S. Vandiver, ibid., 144, 1914, 314-8;
G. Frobenius, Sitzungsber. Ak. Wiss. Beriin, 1910, 200-8; 1914, 653-81.
These papers give further properties of q^.

P. Bachmann^^ employed the identity

(a-\-h-\-cy-{a+b-cy+ia-h-cy-{a-h+cy
= 2(^)cl(a+6r-^-(a-6r-n+2(|)c^l(a+6r-^-(a-6r-^f + ...
for a = 6 = 1, c = 2 or 1 to get expressions for ^2 or q^, whence

for an odd prime p. Comparing this with the value of (3^ — 3)/p obtained
by expanding (2+1)^, we see that

?!ll2_2P-i_^i.2P-2_|_i.2P-3+ , . . +-^-2 (mod p).
p p-l

Again,

92^2- (^) Vssfirn.(s-0 {-ly+'+'s (mod p),
summed for all sets of solutions of s^=f^+l (mod p). Finally,

g2^s'|(r''-r-'')2(r2'"'-l)-i|,

h=l[ " J

where r is a primitive pth root of unity.

*H. Brocard^^ commented on a^^=l (mod p""). *H. G. A. Verkaart^^
treated the divisibility of a^ — a by p. E. Fauquembergue^^ checked that
2^=2 (mod p2) for p = 1093.

N. G. W. H. Beeger^^ tabulated all roots of a;^~^= 1 (mod p^) for each
prime p<200. If w is a primitive root of p^, the absolutely least residue

32aSphinx-Oedipe, 7, 1912, 4-6. It is stated that G. Tarry had verified in 1911 that 2P-2 is

not divisible by a prime p < 1013.
"Sitzungsber. Ak. Wiss. Berlin, 1913, 663-7.
"Jour, fiir Math., 142, 1913, 41-50.

'^Revista de la Sociedad Mat. Espanola, 3, 1913-4, 113-4.
'"Wiskundig Tijdschrift, vol. 2, 1906, 238-240.
"L'interm6diaire des math., 1914, 33.
38Messenger Math., 43, 1913-4, 72-84.

112 History of the Theory of Numbers. [Chap, iv

±xi modulo p2 of CO" is a root, that (^xg) of xi^ is a second root, that ( ^Xg)
of X1X2 is a third root, etc., until the root =tx, is reached, where s = (p-l)/2.
The remaining roots are p^-x,(i = l,. . ., s). He proved that

ixi...xy={-l)-^ (modp2).
Hence Xi. . .x,= ±l if p = 4n+l.

W. Meissner^^ WTote /i^ for the residue <p'" of /i^""' modulo p"*. When
h varies from 1 to p-1, we get p-1 roots h^ of xP-^=1 (mod p"*). The
product of the roots given by h = l,.. ., (p-l)/2, is =(-1)' or (-l)V
(mod p'"), according as p = 4m-1 or 4n+l, where z is the number of pairs
of integers <p/2 whose product is = -1 (mod p), and c is the smaller of
the two roots of x^=-l (mod p). No number <p which belongs to one
of the exponents 2, 3, 4, 6, modulo p, can be a root of x^^=l (mod p^).
A root of the latter is given for each prime p< 300, and a root modulo p^ for
each p<200; also the exponent to which each root belongs.

N. Nielsen^^ noted that, if we select 2r distinct integers a„ &, (s = 1, . . . ,r)
from 1, . . ., p-1, such that a,+b, = p, then

"^ = i-mi-pA), A^ ^ = k^lg^-g^^'j (modp).

Proof is given of various results by Lerch,-^ also of simple relations between
Qa and BernouUian numbers, and of the final formula by Plana,^ here attrib-
uted to Euler.^^

H. S. Vandiver^- proved that there are not fewer than [Vp] and not
more than p — (l + \/2p— 5)/2 incongruent least positive residues of
1, 2^\..., (p-l)^\ modulo f.

N. Nielsen^^ noted that, if a is not di\'isible by the odd prime p,
a — I (p-3)/2 2
9a=-^+ S^ 2j^-ir'i5.(a^-'^-^-l) (modp), j

gi+?2+...+gp-i=(-l)"-'5„+--l (modp2), n=ip-l)/2.

V

W. Meissner^ gave various expressions for ^2 and ^3.

A. G^rardin^^ found all primes p<2000, including those of the form

2"—!, for which 52 is sjTnmetrical when written to the base 2.

H. S. Vandiver^^ proved that 52—0 (mod p^) if and only if

He gave various expressions for (n* — l)/m.

"Sitzungsber. Berlin IMath. Gesell., 13, 1914, 96-107.

"Ann. sc. I'^cole norm, sup., (3), 31, 1914, 171-9.

"Euler, Institutiones Calculi Diff., 1755, 406. Proof, Math. Quest. Educ. Times, 48, 1888, 48.

«BuU. AmQT. Math. Soc, 22, 1915, 61-7.

«K)versigt Danske Vidensk. SeLsk. ForhandUnger, 1915, 518-9, 177-180; cf. Lerch's»» N.

♦^Mitt. Math. Gesell. Hamburg, 5, 1915, 172-6, 180.

«Xouv. Ann. Math., (4), 17, 1917, 102-8.

"Annals of Math., 18, 1917, 112.

CHAPTER V.

EULER'S (^-FUNCTION, GENERALIZATIONS. FAREY SERIES.
Number <f){n) of Integers <n and Prime to n.

L. Euler/ in connection with his generalization of Fermat's theorem,
investigated the number <j){n) of positive integers not exceeding n which are
relatively prime to n, without then using a functional notation for 0(n).
He began with the theorem that, if the n terms a, a-\-d,. . ., a+(n — l)d
in arithmetical progression are divided by n, the remainders are 0, 1,. . .,
n — 1 in some order, provided d is prime to n; in fact, no two of the terms
have the same remainder.

If p is a prime, (^(p"") =p'"~^(p — 1), since p, 2p,. . ., p^~^-p are the only
ones of the p"* positive integers ^ p^ not prime to p"*. To prove that

(1) <t>{AB) =4>{A)<f>{B) {A, B relatively prime),

let 1, a, . . ., CO be the integers <A and prime to A. Then the integers
< AB and prime to A are

1 a . . . CO

A + 1 A+a ... A+co

2A + 1 2A+a ... 2A+C0

(B-l)A+co.

(5-l)A + l {B-l)A-\-a

The terms in any column form an arithmetical progression whose difference
A is prime to B, and hence include <^(J5) integers prime to B. The number
of columns is (f>{A). Hence there are ({>{A)<f){B) positive integers <AB,
prime to both A and B, and hence prime to AB. If p, . . . , s are distinct
primes, the two theorems give

(2) 0(p\ . .s«)=p^-np-l). . .s'-\s-l).

Euler^ later used ttN to denote 4>{N) and gave a different proof of (2).
First, let N = p'^q, where p, q are distinct primes. Among the N—1 integers
<A^ there are p""—! multiples of q, and p'^'^q — l multiples of p, these sets
having in common the p"~^ — 1 multiples of pq. Hence

<^(iV)=iV-l-(p"-l)-(p'*-^g-l)+p"-i-l=p"-i(p-l)(g-l).

A simpler proof is then given for the modified form of (2) :

(3) iV(p-l)to-l)...(.-l),

pq...s
where p, q, r, . . . , s are the distinct primes dividing N. There are N/p
multiples <N of p and hence N' = N{p — \)/p integers <A^ and prime to p.
Of these, N' /q are divisible by q; excluding them, we have N" = N'{q — l)/q
numbers < N and prime to both p and q. The rth part of these are said

^Novi Comm. Ac. Petrop., 8, 1760-1, 74; Comm. Arith., 1, 274, Opera postuma, I, 492-3.
«Acta Ac. Petrop., 4 II (or 8), 1780 (1755), 18; Comm. Arith., 2, 127-133. He took 0(1)=O.

113

114 History of the Theory of Numbers. [Chap, v

[cf. Poinsot^^] to be divisible by r; after excluding them we get N"{r — l)/r
numbers; etc.

Euler^ noted in a posthumous paper that, if p, q, r are distinct primes,
there are r multiples ^pqr of pq, and qr multiples of p, and a single multiple
of pqr, whence

<t){pqr)=pqr-qr-pr-pq-^r+p-\-q-l = {p-l){q-l){r-l).

In general, if M is any number not divisible by the prime p, and if fx
denotes the number of integers ^M and prime to M, there are M—fj.
integers ^M and not prime to M and hence p''{M—ii) integers ^Mp" and
not prime to M and therefore not prime to Mp". Of the Mp^~^ multiples
^Mp^ of p, exclude the p"~^(ilf — /i) which are not prime to M; we obtain
p^'V multiples of p which are prime to M. Hence

<^(p"M)=p"M-p''(M-m)-p""V = P"~Hp-1)m-

A. M. Legendre^ noted that, if ^, . . . , co are any odd primes not dividing
A, the number of terms of the progression A+B, 2A+5, . . . , nA-\-B which
are divisible by no one of the primes 0, . . . , co is approximately n(l — 1/0) . . .
(1 — 1/co), and exactly that number if n is divisible by 0, . . . , co.

C. F. Gauss^ introduced the symbol (i>{N). He expressed Euler's^ proof
of (1) in a different form. Let a be any one of the 4>{A) integers <A and
prime to A, while j8 is any one of the 4>{B) integers <B and prime to B.
There is one and but one positive integer x<AB such that x=a (mod A),
x=^ (mod B). Since this x is prime to A and to B, it is prime to AB.

Making the agreement that <^(1) = 1, Gauss proved

(4) 20(d) =N {d ranging over the divisors of N).

For each d, multiply the integers ^d and prime to d by N/d; we obtain
S0(d) integers ^N, proved to be distinct and to include 1, 2, . . ., iV.

A. M. Legendre^ proved (3) as follows: First, let N = pM, where p is a
prime which may or may not divide M; then Mp—M of the numbers
1,. . ., N are not divisible by p. Second, let N = pqM, where p and q are
distinct primes. Then 1,. . ., N include M numbers divisible by both p
and q; Mp — M numbers divisible by q and not by p; Mq — M numbers
divisible by p and not by q. Hence there remain A^(l — l/p)(l — 1/q) num-
bers divisible by neither p nor q. Third, a like argument is said to apply
to N = pqrM, etc.

Legendre (p. 412) proved that ii A,C are relatively prune and if 0,X,ju, . . . ,
CO are odd primes not dividing A, the number of terms kA — C{k = l,...,n),
which are divisible by no one of 0, . . . , to, is

*Tractatu3 de numerorum, Comm. Arith., 2, 515-8. Opera postuma, I, 1862, 16-17.

*Es3ai siir la thdorie des nombres, 1798, p. 14.

'Disquisitionea Arithraeticse, 1801, Arts. 38, 39.

•Th^orie des nombres, ed. 2, 1808, 7-8; German trans, of ed. 3 by Maser, 8-10.

Chap. V] EulER's (^-FUNCTION. 115

where the summations extend over the combinations of 6,. . ., co taken
1, 2, . . ., at a time, while Aq is a positive integer <A for which ^Aq+C is
divisible by A, and [x] is the greatest integer ^x. We thus derive the
approximation stated by Legendre.^ Taking A = l, C = 0 (p. 420), we see
that the number of integers ^n, which are divisible by no one of the dis-
tinct primes 0, X, . . . , co is

A. von Ettingshausen^ reproduced without reference Euler's^ proof of
(3) and gave an obscurely expressed proof of (4) . Let A'' = p'g" . . . , where
p, q,. . . are distinct primes. Consider first only the divisors d = p^q', where
/i>0, v>0, so that d involves the primes p and q, but no others. By (3),

^(d)=d(i-^) (i-l), J^ |^py=(p+p'+. . .+r)(g+. . .+2"),

S(^(pY) = (p"-i)(/-i).

Similarly, S0(p'') =p"— 1. In this way we treat together the divisors of N
which involve the same prime factors. Hence when d ranges over all the
divisors of N,

S<^(d) = l+S(p«-l) + S(p»-l)(g^-l)+ S (p»-l)(5''_l)(r-_l) + ...

P P.Q P. 3. r

=n]i+(p"-i)J=np"=iv,
p

where the summation indices range over the combinations of all the prime
factors of N taken 1, 2, . . .at a time. [Cf, Sylvester .^^]

A. L. Crelle^ considered the number Zj of integers, chosen from rii, . . . ,na,
which are divisible by exactly j of the distinct primes Pi, . . ., Pm', and the
number Sy of the integers, chosen from rii, . . . , n^, which are divisible by at
least j of the primes Pi. Then

Z1 + Z2+. . .+Zm = Si-S2 + Ss- . . .=tS^.

Let V be the number of the integers rii, . . . , n^ which are divisible by no one
of the primes Pi. Then

a^'Ezi+v, p = a-Si+S2— . . .=PSrr,.

In particular, take nj, ..., ria to be 1, 2,. .., iV, where N = p''q^r^ . . ., and

take Pi,...,Pm to be p, g, r, . . . . Then

N N ^ N N , N ,

P q pq pr ' pqr

cf>{N)=N-s,-{-S2- . . . =n(i--^ 0"-) • • ••

He proved (1) for 5 = 0", where a is a prime not dividing A (p. 40). By
Euler's^ table there are B({)(A) integers <AB and prime to A. In Euler's

^Zeitschrif t fur Physik u. Math, (eds., Baumgartner and Ettmg8hauaen),Wien, 5, 1829, 287-292.
*Abh. Akad. Wiss. Berlin (Math.), 1832, 37-50.

116 History of the Theory of Numbers. (Chap, v

notation, a{kA + l), a{kA-\-a),. . ., a{kA-{-03) give all the numbers between
kaA and {k-\-\)aA which are divisible by a and are prime to A. Taking
A: = 0, 1,. . ., a°~^ — 1, we see that there are exactly a"~V(^) multiples of a
which are <AB and prime to A. Hence

0(a"^) =aXA) -o^-VU) =(t>{a'')(f>{A).

F. Minding^ proved Legendre's formula (5). The number of integers
^n, not divisible by the prime 0, is n — [n/d]. To make the general step
by induction, let Pi, . . . , Pk be distinct primes, and denote by (5; pi, . . . , p^)
the number of integers ^ 5 which are divisible by no one of the primes pi, . . . ,
Pk' Then, if p is a new prime,

(B; pi, . . . , Pk, p) = {B;pu..., Pk) - ([B/p] ; Pi, . • • , Pk)-

The truth of (4) for the special case N = p — 1, where p is a prime, follows
(p. 41) from the fact that ((){d) numbers belong to the exponent d modulo p
if d is any divisor of p — 1.

N. Druckenmiiller^*^ evaluated (f>{b), first for the case in which 6 is a
product cd. . .kl oi distinct primes. Set h=^l and denote by \f/{h) the num-
ber of integers <b having a factor in common with 6. There are l\p{^)
numbers < b which are divisible by one of the primes c, . . . , k, since there
are \p{P) in each of the sets

l,2,...,/3; ^+1,...,2^; ...; (i-l)/3+l,. . ., Z/3.

Again, I, 21,..., pi are the integers <b with the factor I. Of these, 0(j3)
are prime to jS, while the others have one of the factors c, . . . , k and occur
among the above lxl/{^). Hence xl/{b)=l\l/i^)-\-<i>iP). But i/'O3)+0(/3)=/3.
Hence

</,(6) = a-l)(A(^) = (c-l)...(Z-l).

Next, let 6 be a product of powers oi c, d,. . ., I, and set b = L^, ^ = cd. . .1.
By considering L sets as before, we get

E. Catalan^^ proved (4) by noting that

2(/,(py. . .)=n]i+(/)(p)+ . . . +<f>(p'')\ =np»=Ar,

where there are as many factors in each product as there are distinct prime
factors of N.

A. Cauchy^^ gave without reference Gauss'^ proof of (1).

E. Catalan^^ evaluated <t){N) by Euler's^ second method.

C. F. Arndt^"* gave an obscure proof of (4), apparently intended for
Catalan's. ^^ It was reproduced by Desmarest, Th^orie des nombres, 1852,
p. 230.

•Anfangsgriinde der Hoheren Arith., 1832, 13-15.
»oTheorie der Kettenreihen . . .Trier, 1837, 21.
"Jour, de Mathdmatiques, 4, 1839, 7-8.
i»Compte8 Rendus Paris, 12, 1841, 819-821; Exercices d'analyse et de phys. math., Paris, 2,

1841, 9; Oeuvres, (2), 12.
"Nouv. Ann. Math., 1, 1842, 466-7.
"Archiv Math. Phys., 2, 1842, 6-7.

Chap. V] EuLER's (^-FUNCTION. 117

J. A. Grunert^^ examined in a very elementary way the sets
jk+1, jk-{-2,..., jk+k-l, {j+l)k (j = 0, l,...,p-l)
and proved that 4){'pk)='p4){k) if the prime p divides k, while 4){pk) =
(p — l)<j){k) if the prime p does not divide k. From these results, (2) is
easily deduced [cf. Crelle^^ on (f){Z)].

L. Poinsot^® gave Catalan's^^ proof of (4) and proved the statements
made by Euler^ in his proof of (3) . Thus to show that, of the N' = N{1- 1/p)
integers < N and prime to p, exactly N'/q are divisible by q, note that the
set 1,. . ., N contains N/q multiples of q and the set p, 2p, . . . contains
{N/p)/q multiples of q, while the difference is N'/q.

If P, Q, R,. . . are relatively prime in pairs, any number prime to
N = PQR . . . can be expressed in the form

pQR...+qPR...+rPQ... + ...,

where p is prime to P, q to Q, etc. If also p<P, q<Q, etc., no two of these
sums are equal. Thus there are 0(P)0(Q) . . . such sums [certain of which
may exceed N].

To prove (4), take (pp. 70-71) a prime p of the form kN+l and any one
of the N roots p of a;^= 1 (mod p). Then there is a least integer d, sl divisor
of N, such that p'^= 1 (mod p). The latter has (f)(d) such roots. Also p is a
primitive root of the last congruence and of no other such congruence whose
degree is a divisor of N.

A. L. Crelle^^ considered the product E = eie2. . .e„ of integers relatively
prime in pairs, and set Ej = E/ej. When x ranges over the values 1, . . ., Ci,
the least positive residue modulo E of EiXi-\- . . . +£'„a;„ takes each of the
values 1, . . .,E once and but once. In case Xi is prime to ei for i = 1, . . . , n,
the residue of SE'^Xi is prime to E and conversely. Let dn, di2, ... be any
chosen divisors >1 of e^ which are relatively prime in pairs. Let \}/{ei)
denote the number of integers ^e^ which are divisible by no one of the
^ti, di2,. . .. Let yl/{E) be the number of integers ^E which are divisible
by no one of the dn, di2, c^2ij ■ ■ •> including now all the d's. Then \1/{E) =
^(ei) . . . i/'(en). In case dn, di2, . . . include all the prime divisors > 1 of e,-,
ypie^ becomes ^(e^). Of the two proofs (pp. 69-73), one is based on the
j&rst result quoted, while the other is like that by Gauss .^

As before, let ^{y) be the number of integers '^y which are divisible by
no one of certain chosen relatively prime divisors di,...,dm of y. By con-
sidering the xy numbers ny-\-r (0^n<x, I'^r^y), it is proved (p. 74) that,
when X and y are relatively prime,

ypixy) =x\p{y), \p2ixy) = {x-l)xl/{y),

where \p2{^y) is the number of integers ^xy which are divisible neither by
X nor by any one of the d's. These formulas lead (pp. 79-83) to the value
of0(Z). Set
Z = p/'...p/M, z = Pi...p^, n = Z/z,

i^Archiv. Math. Phys., 3, 1843, 196-203.

"Jour, de Math^matiques, 10, 1845, 37-43.

"Encyklopadie der Zahlentheorie, Jour, fiir Math., 29, 1845, 58-95.

118 History of the Theory of Numbers. [Chap, v

where Pi,. . ., p^ are distinct primes. For a prime p, not dividing y, we
have (f){py) = {p- l)<t>iy) . Take y = Pi, p = P2', then

<^(PiP2) = (Pi-l)(P2-l)-
Next, take y = PiP2, P = P3} and use also the last result; thus

<A(PlP2P3) = (Pl-l)(P2-l)(P3-l),

and similarly for <t){z). When f ranges over the integers < z and prime to z,
the numbers vz-\-^ {v = 0,l,. . .,n — l) give without repetition all the integers
<Z and prime to Z. Hence (f>{Z)=n<i){z), which leads to (2). [Cf. Guil-
min,2^ Steggall.'^^]

The proofs of (4) by Gauss^ and Catalan^ ^ are reproduced without refer-
ences (pp. 87-90). A third proof is given. Set N = a''h^c' . . ., where a, b,
c, . . . are distinct primes. Consider any divisor e = b^"^' . . . of N such that e
is not divisible by a. Then

<t>i€a'')=a''-\a-l)(t>{e).

Sum for /b = 0, 1, . . . , a; we get a°0(e). When k ranges over its values and
/3i over the values 0, 1,. . ., j3, and 71 over the values 0, 1,. . ., 7, etc., ea*
ranges over all the divisors d of iV. Hence 20 (d) =a''S0(e). Similarly, if
Ci range over the divisors not divisible by a or b,

S</)(€)=6^(^(ei),. . ., S<^(d)=a»6^ . . =N.

E. Prouhet^^ proposed the name indicator and symbol i{N) for 0(iV).
He gave Gauss' proof of (1) and Catalan's proof of (4). If 5 is the product
of the distinct prime factors common to a and b,

<j>{ab) =(i>{a)(}>ib)8/(f){8).

As a generalization, let 5^ be the product of the distinct primes common to
i of the numbers Oi, . . . , a„; then

2 § 2 2 n-l

</)(ai. . .a„) =<j>{ai) . . .<f){an) ^ ^

Friderico Arndt^^ proved (1) by showing that, if x ranges over the
integers <A and prime to A, while y ranges over the integers <B and prime
to B, then Ay-{-Bx gives only incongruent residues modulo AB, each prime
to AB, and they include every integer <AB and prime to AB. [Crelle's^^
first theorem for n = 2.]

V. A. Lebesgue^° used Euler's^ argument to show that there are

Nip-l){q-l)...{k-l)
p-q. . .k

integers < iV and prime top,q,...,k, the latter being certain prime divisors
of A'' [Legendre,^ Minding^].

"Nouv. Ann. Math., 4, 1845, 75-80.
"Jour, fur Math., 31, 1846, 246-8.
"Nouv. Ann. Math., 8, 1849, 347.

Chap. V] EuLER's 0-FuNCTION. 119

G. L. Dirichlet^^ added equations (4) for iV = n, . . ., 2, 1, noting that,
if s^n, 4>(s) occurs in the new left member as often as there are mul-
tiples ^n oi s. Hence

i\-']<f>{s)=Un'+n).

s=lLsJ

The left member is proved equal to XxJ/in/s], where

It is then shown that \p{n) —Zn^/ir^ is of an order 6i magnitude not exceed-
ing that of n\ where 2>5>7>1,7 being such that

8=2 S^

P. L. Tchebychef^^ evaluated 0(n) by showing that, if p is a prime not
dividing A, the ratio of the number of integers ^ pAN which are prime to A
to the number which are prime to both A and p is p:p — l.

A. Guilmin^^ gave Crelle's^^ argument leading to 0(Z).

F. Landry ^^ proved (3). First, reject from 1, . . ., iV the N/p multiples
of p; there remain A^(l — 1/p) numbers prime to p. Next, to find how many
of the multiples q, 2q, . . . , N of q are prime to p, note that the coefficients
1, 2, . . ., N/q contain N/q-{l — l/p) integers prime to p by the first result,
applied to the multiple N/q of p in place of N.

Daniel Augusto da Silva^^ considered any set S of numbers and denoted
by S{a) the subset possessing the property a, by S{ab) the subset with the
properties a and b simultaneously, by {a)S the subset of numbers in S
not having property a; etc. Then

{a)S = S-S{a)=S\l-{a)\,

symbolically. Hence

(ha)S = {b)\(a)S\=S\l-{a)\\l-{h)\,
{. . .cba)S^S\l-{a)\\l-{b)\ \l-{c)\ . . ..

A proof of the latter symbohc formula was given by F. Horta.^^"
With Silva, let *S be the set 1, 2, . . . , n, and let A, ^, . . . be the distinct
prime factors of n. Let properties a, 6, ... be divisibility by A,B,. . .. Then
there are n/A terms in >S(a), n/{AB) terms in S{ab), . . ., and <f){n) terms in
( . . .cba)S. Hence our symbolic formula gives

*(«)=»(l-i)(l-|).

"Abhand. Ak. Wiss. Berlin (Math.), 1849, 78-81; Werke, 2, 60-64.

^^Theorie der Congruenzen, 1889, §7; in Russian, 1849.

«Nouv. Ann. Math., 10, 1851, 23.

^^Troisieme mlmoire siir la th^orie des nombres, 1854, 23-24.

'^Proprietades geraes et resoluQao directa das Congruencias binomias, Lisbon, 1854. Report
on same by C. Alasia, Rivista di Fisica, Mat. e Sc. Nat., Pavia, 4, 1903, i3-17; reprinted
in Annaes Scientificos Acad. Polyt. do Porto, Coimbra, 4, 1909, 166-192.

""Annaes de Sciencias e Lettras, Lisbon, 1, 1857, 705.

120 History of the Theory of Numbers. [Chap, v

E. Betti^® evaluated 0(w), where 7n is a product of powers of the distinct
primes ai, a2> • •• • Consider the set Ci of the products of the a's taken i at
a time and their multiples ^m. Thus Co is 1, . . . , w, while C2 is

0x02, 20x02, . . ., 0102; cii(h, 2ai03, . . ., diCis',- ■ ••

aia2 ttitta

Let X be an integer < w divisible by ai, . . . , a„. Then x occurs

times in the sets Co, C2, C4, . . . ; and 2" ^ times in Ci, C3, . . .. Summing

l-(l) + (2)-(3)+ =0

for each of the m—<t>{m) integers ^m having factors in common with m,
we get

m-0(m)-s(j)+s(2)-...=O.

But ^i-i) is the niunber of integers having in common with m one of the
factors ai, 02, . . ., and hence equals S— . Next, ^i^j ^^ *^® number of

integers having in common with m one of the factors 0102, OiOa, . . . , and hence

equals 2 { m/ (0102) } . Thus

mm
4>{m) =m—L, — 1-2 ....

R. Dedekind^^ gave a general theorem on the inversion of functions (to
be explained in the chapter on that subject), which for the special case of
</)(n) becomes a proof like Betti's. Cf. Chrystal's Algebra, II, 1889, 511;
Mathews' Theory of Numbers, 1892, 5; Borel and Drach,^^ p. 27.

J. B. Sturm^^ evaluated 4>{N) by a method which will be illustrated for
the case N = \b. From 1,. . ., 15 delete the five multiples of 3. Among
the remaining ten numbers there are as many multiples of 5 as there are
multiples of 5 among the first ten numbers. Hence <^(15) = 10—2 = 8.
The theorem involved is the following. From the three sets

1, 2, 3,* 4, 5; 6,* 7, 8, 9,* 10; 11, 12,* 13, 14, 15*

delete (by marking with an asterisk) the multiples of 3. The numbers
11, 13, 14 which remain in the final set are congruent modulo 5 to the num-
bers 6, 3, 9 deleted from the earUer sets.

J. Liouville" proved by use of (4) that, for |x|<l,

g <t>{m)x"' _ X (t>{m)x"'_ g <f>{m)x'^ _x{l-\-x^)

m^ll-X"^ ~{l-xf l-X^^'m^ll+X"" ~{1-Xy '

"Bertrand's Alg^bre, Ital. transl. with notes by Betti, Firenze, 1856, note 5. Proof reproduced

by Fontebasso'*, pp. 74-77. ^

"Jour, fvir Math., 54, 1857, 21. Dirichlet-Dedekind, Zahlentheohe, §138. ^

"Archiv Math. Phys., 29, 1857, 448-452.
"Jour, de math6matiques, (2), 2, 1857, 433^40.

Chap. V] EuLER's (^-FUNCTION. 121

where m in S' ranges only over the positive odd integers. The final fraction
equals x-\-Sx^-{-5x^+ .... From the coefficient of x^ in the expansion of
the third sum, we conclude that, if n is even,

where d ranges over all the divisors of n. Let 5i range over the odd values
of 5, and 82 over the even values of 5; then

0-0-

the value n/2 following from (4). Another, purely arithmetical, proof is
given. Finally, by use of (4), it is proved that, if s>2,

n=l /fr n=l/t

A. Cayley3° discussed the solution for N of <^(iV) = iV^ Set N = a^b^ ...,
where a, 6, . . . are distinct primes. Multiply

l + (a-l) \a\+a{a-l) \a^\ + ... +a''-\a-l) {a"} + . . .

by the analogous series in 5, etc. ; the bracketed terms are to be multiplied
together by enclosing their product in a bracket. The general term of the
product is evidently

Hence in the product first mentioned each of the bracketed numbers which
are multiplied by the coefficient N' will be a solution N of <f){N)=N'. We
need use only the primes a for which a — 1 divides N', and continue each
series only so far as it gives a divisor of N' for the coefficient of a"~^(a — 1).

V. A. Lebesgue^^ proved 4){Z)=n4>{z) as had Crelle^^ and then 4>{z)
=n(pi — 1) by the usual method of excluding multiples of pi, . . . , p„ in turn.
By the last method he proved (pp. 125-8) Legendre's (5), and the more
general formula preceding (5).

J. J. Sylvester^^ proved (4) by the method of Ettingshausen,' using (2)
instead of (3) . By means of (4) he gave a simple proof of the first formula
of Dirichlet;^^ call the left member u^', since [n/r] — [(n — l)/r] = l or 0,
according as n is or is not divisible by r,

v^^J^ w(n+l)

The constant c is zero since Ui = l. He stated the generalization

2{*(i')(l-+2-+... + [?]'")}^

r+2'-+...+n'".

He remarked that the theorem in its simplest form is

"London Ed. and Dublin Phil. Mag., (4), 14, 1857, 539-540.

"Exercicea d'analyse niim^rique, 1859, 43-45.

"Quar. Jour. Math., 3, 1860, 186-190; CoU. Math. Papers, 2, 225-8.

122 History of the Theory of Numbers. [Chap, v

the example given being r = 2, n = 4, whence the divisors of n are 1-1, 2-1, 4-1,
1-2, 2-2, 1-4 and the above terms are

Ml, Ml, M-2, 2-M, 2M, 4-21,

with the sum 4". [With this obscure result contrast that by Cantor/^]

G. L. Dirichlet^^ completed by induction Euler's^ method of proving (3),
obtaining at the same time the generalization that, if p, g, . . . , s are divisors,
relatively prime in pairs, of N, the number of integers ^ N which are divi-
sible by no one of p, . . . , s is

H-;)04) 0--.)

A proof (§13) of (4) follows from the fact that, if d is a divisor of N, there
are exactly </)(d) integers ^N having with N the g. c. d. N/d.

P. A. Fontebasso^^ repeated the last remark and gave Gauss' proof of (1).

E. Laguerre^^ employed any real number k and integer m and wrote
(m, m/k) for the number of integers ^m/k which are prime to m. By
continuous variation of k he proved that

i:{d,d/k) = [m/k],

where d ranges over the divisors of m. For k = l, this reduces to (4).

F. Mertens^^ obtained an asymptotic value for 0(1)+ . . . +(i>iG) for G
large. He employed the function ju(n) [see Ch. XIX] and proved that

I 0(m) = | S /.(n){r^lVr^l U^GHA
TO=i n=i iLnJ Lnjj tt

|A|<G(ilog,G+iC+f) + l,

where C is Euler's constant 0.57721 .... This upper limit for A is more
exact than that by Dirichlet.^^

T. Pepin^'' stated that, if n = a"6^. . . (a, 6, . . .distinct primes),

n=0(n)+2a»-V(^) +2a-V-^(/,(^) + . . . -\-a-'b'-'. . ..

Moret-Blanc^^ proved the latter by noting that the first sum is the num-
ber of integers < n which are divisible by a single one of the primes a, 6, ... ,
the second sum is the number of integers < n divisible by two of the primes,
. . ., while a''~^6^~\ . . is the number of integers <n divisible by all those
primes.

H. J. S. Smith^^ considered the m-rowed determinant A„, having as the
element in the ith. row and jth column the g. c. d. {i, j) of i, j. Let li = m,

"Zahlentheorie, §11, 1863; ed. 2, 1871; ed. 3, 1879; ed. 4, 1894.

»*Saggio di una introd. all'arit. trascendente, Treviso, 1867, 23-26.

«BuU. Soc. Math. France, 1, 1872-3, 77.

»«Jour. fiir Math., 77, 1874, 289-91.

»'Nouv. Ann. Math., (2), 14, 1875, 276.

"/bid., p. 374. L. Gegenbauer, Monatsh. Math. Phys., 4, 1893, 184, gave a generahzation to

primary complex numbers.
»»Proc. London Math. Soc, 7, 1875-6, 208-212; CoU. Papers, 2, 161.

Chap. V] EulER's </)-FuNCTION. 123

I2, I3,... be those divisors of m = p V • • • ^'^ which are given by the expansion
of the product

0(m) = (p--p"-i). . .(r-r-i)=?i-Z2+?3-. . .-^v

It is proved that

cl>{m, k) = {k, k)-{k, k)+ . . . -{I, k)

[called Smith's function by Lucas/^ p. 407] is zero if k<m, but equals
<^(m) if ^ = m. Hence if to the mth column of A^ we add the columns with
indices I3, I5,... and subtract the columns with indices I2, Z4, . . . , we obtain
an equal determinant in which the elements of the mth column are zero
with the exception of the element <^(m). Hence A^=A^_i0(m), so that

(6) A^=<^(l)0(2)...0(m).

If we replace the element 5 = {i, j) by any function /(5) of 5, we obtain a
determinant equal to i^(l) . . .F{m), where

nm)=/W-2/g)+S/g)-.,..

Particular cases are noted. For /(§) = S''', F{m) becomes Jordan's^"" func-
tion Jkitn). Next, if /(5) is the sum of the kth. powers of the divisors of 5,
then F{m)='m!'. Finally, if /(6) = 1^+2^+ . . . +5^, it is stated erroneous-
ly that F{m) is the sum (i>k{'m) of the /bth powers of the integers ^m and
prime to m. [Smith overlooked the factors o!', oJ^h^, ... in Thacker's^^° first
expression for <l>k{n), which is otherwise of the desired form F{n). The
determinant is not equal to 4>k{\) . . .^^kim), as the simple case k = l, w = 2,
shows.]

In the main theorem we may replace 1,. . ., m by any set of distinct
numbers jui, . . . , jU;„ such that every divisor of each ju, is a number of the
set; the determinant whose element in the ith. row and jth column is/(5),
where 5 = (jUi, /xy), equals F()Ui) . . .F{fx^. Examples of sets of ^t's are the
numbers in their natural order with the multiples of given primes rejected;
the numbers composed of given primes; and the numbers without square
factors.

R. Dedekind^° proved that, if n be decomposed in every way into a
product ad, and if e is the g. o,. &. oi a, d, then

S|.#,(6) = nn(l+^),

where a ranges over all divisors of n, and p over the prime divisors of n.

P. Mansion^^ stated that Smith's relation (6) yields a true relation if we
replace the elements 1,2,. . .of the determinant A^ by any symbols Xi,X2,. . .,
and replace 0(m) by Xi^—Xi^-\-Xi — .... [But the latter is only another
form of Smith's F{m) when we write x^ for Smith's /(5), so that the generali-
zation is the same as Smith's.]

"Jour, ftir Math., 83, 1877, 288. Cf. H. Weber, Elliptische Functionen, 1891, 244-5; ed. 2,

1908 (Algebra III), 234-5.
^Messenger Math., 7, 1877-8, 81-2.

124 History of the Theory of Numbers. [Chap, v

P. Mansion^^ proved (6), showing that </>(m, k) equals <f){m) or 0, accord-
ing as m is or is not a divisor of k. [Cf. Bachmann, Niedere Zahlentheorie,
I, 1902, 97-8.] He repeated his*^ ''generalization." He stated that if a
and b are relatively prime, the products of the 0(a) numbers <a and prime
to a by the numbers <b and prime to b give the numbers <ab and prime
to ab [false for a =4, 6 = 3; cf. Mansion^]. His proof of (4) should have
been credited to Catalan."

E. Catalan^^ gave a condensation and shght modification of Mansion's*'
paper. C. Le Paige {ibid., pp. 176-8) proved ]\Iansion's^ theorem that
every product equals a determinant formed from the factors.

P. IMansion"" proved that the determinant |cy| of order n equals rriX2- • x^
if Cij=Xxp, where p ranges over the divisors of the g. c. d. of i, j. To obtain
a "generahzation" of Smith's theorem, set Zi = Xi, Z2 = Xi-{-X2,. . ., Zi=J>Xi,
where d ranges over all the divisors of i. Solving, we get

where the Vs are defined above.^^ Thus each Cy is a z. For example, if n = 4, -

21

21

2l

2l

Zi

22

2l

22

Zl

2l

23

2i

21

22

2l

24

Cii =

For Zi = i, Xi becomes 4>{i) and we get (6). [As explained in connection with
Mansion's*^ first paper, the generaUzation is due to Smith.]

J. J. Sylvester^^ called (/)(7i) the totient T{n) of n, and defined the totitives
of n to be the integers < n and prime to n.

F. de Rocquigny^^ stated that, if ^"(A^) denotes <l)\(i>{N)\ , etc.,

if A^ is a prime and m>2, p>2. He stated incorrectly (ibid., 50, 1879, 604)
that the number of integers ^ P which are prime to N = a^b^ ... is P(l — 1/a)
(1-1/6)....

A. Minine*^ noted that the last result is correct for the case in which
P is divisible by each prime factor a, b,. . . oi N. He wrote symbolically

nE— for [n/x], the greatest integer ^n/x. By deleting from 1, . . ., P the

[P/a] numbers di\'isible by a, then the multiples of 6, etc., we obtain for
the number of integers ^ P which are prime to N the expression

[equivalent to (5)]. If N, N', N", ... are relatively prime by twos,

♦^Annalea de la Soc. Sc, Bru.\elles, 2, II, 1877-8, 211-224. Reprinted in Mansion's Sur la

th^orie des nombres, Gand, 1878, §3, pp. 3-16.
"Nouv. Corresp. Math., 4, 1878, 103-112.
«Bull. Acad. R. Sc. de Belgique, (2), 46, 1878, 892-9.

«Amer. Jour. Math., 2, 1879, 361, 378; Coll. Papers, 3, 321, 337. Nature, 37, 1888, 152-3.
«Le8 Mondes, Revue Hebdom. des Sciences, 48, 1879, 327.
"Ibid., 51, 1880, 333. Math. Soc. of Moscow, 1880. Jour, de math. 616in. et sp^c, 1880, 278.

Chap. V] EulEr's 0-FunCTION. 125

cf>{N)p-(t>iN')prcf>{N")p.. . . =<f>(NN'Nr . .)p'P'P". . ..
E. Lucas^^ stated and Radicke proved that

a=l fc=2 0=1 k=2

if ^(a, n) is the number of integers > a, prime to a and ^ n.
H. G. Cantor^^ proved by use of ^-functions that

Svo^-Vr". . .vU24>M4>{vi) . . .0(^-i) ^n",
summed for all distinct sets of positive integral solutions Vq,..., v^^i of
Vq. . .Vp=n, and noted that this result can be derived from the special case (4).
0. H. MitchelP° defined the a-totient Taik) of k^a'b''. . . (where a,h,. ..
are distinct primes) to be the number of integers <k which are divisible
by a, but by no one of the remaining prime factors 6, c, ... of k. Similarly,
the a6-totient Tabik) of k is the number of integers <k which are divisible
by a and h, but not by c, . . . ; etc. If /c = a'6V,

tM =a'-V(&V), Ta,{k)=a'-'h--'<t>{c^), TaUk)=a'-'b^-'c'-\
<f>ik) +2t,(A;) +2ra,(/c) +Tadk) = k.

3 3

If a contains the same primes as s, but with the same exponents as in k, so
that o- = a' if s = a, it is stated (p. 302) that

■w=i*a-

C. Crone" evaluated (^(n) by an argument valid only when n is a product
of distinct primes Pi,...,Pq. The number of integers <n having a factor
in common with n is then

A=2(ii-l)-s(^-l) + ...+(-l).2(^^ 1).

The sum of the second terms of each sum is

-(0+a)- -(-^)'G^)=-i-(-i)"-

Hence the number of integers <n and prime to n is

n-\-A=n-l^—^^— — . . . -(-1)«S +(-!)«

Pi V\V2 Pl-Pg-l

provided n = pi. . .pg. [To modify the proof to make it vahd for any n,
we need only add to A the term

and hence replace (-1)*' by (-l)%/(pi. . .p^) in n-l-A.]

*8Nouv. Corresp. Math., 6, 1880, 267-9. Also Lucas, '^ p. 403.
"Gottingen Nachrichten, 1880, 161; Math. Ann., 16, 1880, 583-8.
"Amer. Jour. Math., 3, 1880, 294.
"Tidsskrift for Mathematik, (4), 4, 1880, 158-9.

126 History of the Theory of Numbers. [Chap. V

Franz Walla^- considered the product P of the first n primes > 1. Let
a*i, . . . , X, be the integers <P/2 and prime to P, so that v=4>{P)/2. Then,
if n>2, half of the x's are =1 (mod 4) and the others are =3 (mod 4).
Also, the absolute values of \P — 2Xj (j = 1, . . . , v) are the a:'s in some order.
Half of the a:'s are <P/4.

J. Perott^^ proved that

the context showing that the summations extend over all the primes p< for
which Kpi^N [Lucas"]. He proved that

lim ^jN) _ 3
iV = «) m 7r2

and gave a table showing the approximation of SN^/tt^ to $(iV) for iV^ 100.
The last formula, proved earlier by Dirichlet^^ and Mertens,^^ was proved
by G. H. Halphen^^ by the use of integrals and f -functions.

Sylvester^*" defined the frequency 5 of a divisor d of one or more given
integers a, h, . . . , I to he the number of the latter which are divisible by
d. By use of (4) he proved the generalization

X8(f>{d)=a+h-\-...-\-l.

d

J. J. Sylvester^^ stated that the number of [irreducible proper] fractions
whose numerator and denominator are ^j is T{j) = <f){l)+ . . . +<t>{j), and

that 3 PoT •'" f-'/^] n^-\-i

stU^s S(/,(t)=^,

k=i L/CJ ^=1 i=i ^

whence T{j)/f approximates S/tt^ as j increases indefinitely.

If u{x) denotes the sum of all the integers <x and prime to x, and if
U(j)=u(l)+ . . .-{-u(j), then U{j) is the sum of the numerators in the
above set of fractions, and*

When j increases indefinitely, U{j)/f approximates I/tt^. For each integer
n^ 1000 the values of (^(n), T{n), Srr/ir'^ are tabulated,

Sylvester^^ stated the preceding results and noted that the first formula
is equivalent to

!I3^^^)

l(/+i).

"Archiv Math. Phys., 66, 1881, 353-7.

"Bull, des Sc. Math, et Astr., (2), 5, I, 1881, 37-40.

"Comptes Rendua Paris, 96, 1883, 634-7.

"«Amer. Jour. Math., 5, 1882, 124; Coll. Math. Papers, 3, 611.

"Phil. Mag., 15, 1883, 251-7; 16, 1883, 230-3; Coll. Math. Papers, 4, 101-9. Cf. Sylvester."

"Comptes Rendus Paris, 96, 1883, 409-13, 463-5; Coll. Math. Papers, 4, 84-90. Proofs by

F. Rogel and H. W. Curjel, Math. Quest. Educ. Times, 66, 1897, 62-4; 70, 1899, 56.
*With denominator 3, but corrected to 6 by Sylvester," which accords with Ces&,ro." The

editor of Sylvester's Papers stated in both places that the second member should be

jij + l){2j+l)/12, evidently wrong for; =2.

Chap. V] EulEE's (^-FUNCTION. 127

E. Ces^ro^^ proved that, if / is any function,

X^i^Xx^Fin), F(n)^S/(d),

n = ll X 71=1

where d ranges over the divisors of n. For / = 0, we have F(x)=x and obtain
Liouville's^^ first formula. By the same specialization (p. 64) of another
formula (given in Chapter X on sums of divisors^^), Cesaro derived the
final formula of Liouville.^^ If (n, j) is the g. c. d. of n and j, then (p. 77,
p. 80)

Mn, j) =S#Q), X-^ = h:d<t>{d), X4>{n, j) =S(^(d)0(-).

If (p. 94) p is one of the integers a, /3, . . . ^ n and prime to n,

S^(a)F(a) =SG(a)/(a), /^(a:)^S/(d), G(p)^S^(pa),

a

where d ranges over the divisors of x. For g{x) = l, this gives

S/(a)0(n, n/a)=SF(a),

a

where (p. 96) </)(n, x) is the number of integers ^x and prime to n. Cesaro
(pp. 144-151, 302-3) discussed and modified Perott's^^ proof of his first
formula, criticizing his replacement of [n/k] by n/k for n large. He gave
(pp. 153-6) a simple proof that the mean^^ of <^(n) is Qn/w^ and reproduced
the proofs by Dirichlet^^ and Mertens,^^ the last essentially the same as
Perott's. For Kw) = l + l/2"^+l/3"+. . .,

s4r(^>l), 2i 2-i-(m>l), 2-^

a"* ' '' a' a'"</)(a) ' '' 0(a)

equal asymptotically (pp. 167-9)

f(m)/r(m+l), (6 1og7i)/7r^ r(m+l), log n.

As a corollary (p. 251) to Mansion's^^ generalization of Smith's theorem we
have the result that the determinant of order n^, each element being 1 or 0
according as the g. c. d. of its two indices is or is not a perfect square, equals
( — 1)"+^+- , where pV- • • is the value of n\ expressed in terms of its prime
factors.

Ces^ro^* considered any function F{x, y) of the g. c. d. of x, y, and the
determinant A„ of order n having the element F{Ui, u/) in the ith. row and
ith column, where Ui,...,Un are integers in ascending order such that each
divisor of every Ui is a u. Employing the function ix{n) [see Ch. XIX], he
noted that

i nO^)F(u„ud=f{u,) or 0,

"M6m. Soc. R. Sc. de LiSge, (2), 10, 1883, No. 6, 74.
"Atti Reale Accad. Lincei, (4), 1, 1884-5, 709-711.

128 History of the Theory of Numbers. [Chap, v

according as u^ is or is not divisible by w„, while

fix) =Kx)F{l) +M (2) F{2) +M (f) F{S) + . . . .

Hence if we multiply the elements of the ith colmnn of A„ by fx{ujui) and
add the products to the last column for 2 = 1, . . ., n — 1, the new elements of
the last colunm are zero except the final element, which is/(w„). Thus

A,=/(ii„)A„_i=/(ui)/(w2) . . .fM-

[These results are due to Smith,^^ not merely the case Ui = i a.s stated.]
Cesaro^^ noted that |wy|=/(l) . . ./(n) if

«,= s/wft0ft.Q,

where the function h has the property that the determinant with the general
element h{i/j) is unity, and similarly for hi.

Cesaro®° gave the last result for the case in which h{x)=hi{x) = l or 0
according as x is or is not an integer. P. Mansion (p. 250) stated that he**
had employed a similar proof.

Ces^ro®^ duphcated his paper^^ and transformed its final result into

/(l)/(2) . . .fin)

F[i,j]

F\nl)

where [i, j] = ij/{i, j) is the 1. c. m. of i, j, and F{x) is a function such that
F{xy)=F{x)F{y). In particular, if F{x) = \/x, then J{x)=4){x)Tr{x)/x^,
where 7r(n) is the product of the negatives of the distinct prime factors of n.
Hence

|Ki]|n=0(l)...0(n)7r(l)...7r(n).

Ces^ro^^ investigated the r-rowed minors of the n-rowed determinant
whose general element is F{b)=F{i, j), where 5 is the g. c. d. of i, j. It is
shown that the {n — v)-Towed determinant whose general element is F{i-\-v,
j-\-v) is equal to the sum of certain products of /(I), . . ., f{n) taken n — v&i
a time, the case v = Q being Smith's theorem. Here

/(x) =^J^F{j), Fix) =S/(d) (d divisor of x).

Ces^ro^^ stated that the (n — l)-rowed determinant, whose general ele-
ment Uij equals the number of divisors common to i+1 and j + 1, equals
the number of integers ^ n deprived of square factors > 1 .

"Atti. Reale Accad. Lincei, (4), 1, 1884-5, 711-5.

•"Mathesis, 5, 1885, 248-9.

"Giornale di Mat., 23, 1885, 182-197.

"Annales de I'^cole normale sup., (3), 2, 1885, 425-435.

"Nouv. Ann. Math., (3), 4, 1885, 56.

Chap. V] EulEE's (^-FUNCTION. 129

Ces^ro" employed F(n)=S/(d), G(n)='Zg{d), where d ranges over the
divisors of n, and proved that

0 G(l) G{2) ... G{n)

G{\) F(l,l) F(l,2) ... F(l,n) -_j(i)..j(^)p'(^),

G{n) F{n,l) F{n,2) Fin, n)

In particular, if F{n) is the number of divisors of n and if G{n) is the number
of prime divisors of n, the determinant, apart from signs, equals the number
of primes ^ n.

E. Cesaro^^ wrote (a, b) for the g. c. d. of a, h. If F{n) =S/(d), where d
ranges over the divisors of n, then

XF\(n,i)\=i:f(d)N/d.

In particular, if /,(n) is the number of irreducible fractions ^e of denomi-
nator n.

IXn)=i:[j]n{d), S7,(d) = [ne].

The last formula, due to Laguerre,^^ follows by inversion (Ch. XIX), and
directly from the fact that I^d) is the number of the first [ne] integers which
with n have the g. c. d. n/d. The number of irreducible fractions ^ e of
denominator ^n is $e(^) =-f «(!)+••• +-^.(^). We have

00 \n/j] O,

^M = SmO') S [ie], Imi $,(n)/n2 = -2 (€>0),

j = l 1=1 n=oo T

due to Sylvester^^ for € = 1. Let (^^g^(n) be the sum of the j'th powers of
the numerators of the irreducible fractions < e of denominator n. Set

Then

$« in) = S </)(? ii) , sXn) = S ^^
1=1 »-i

i=l LzJ i.i

which generalizes the two formulas of Sylvester .^^ Also,
$^;^ (w) = — — — — — , asymptotically.

TT V-\-l V-\-2

Ces^ro^^" factored determinants of the tj^e in his paper,^^ the function F
now being such that Fixy)/ \Fix)Fiy)\ is a function of the g. c. d. oi x, y.

L. Gegenbauer®^'' gave a complicated theorem involving several general
functions, special cases of which give Sylvester's^^ two summation formulas.

"Nouv. Ann. Math., (3), 5, 1886, 44-47.

"Annali di Mat., (2), 14, 1886-7, 143-6.

""Giornale di Mat., 25, 1887, 18-19.

«5fcSitzungsber. Ak. Wiss. Wien (Math.), 94, 1886, II, 757-762.

130 History of the Theory of Numbers. [Chap, v

P. S. Poretzky^^ gave a formula for the function \l/{m) whose values are
the 4>{7?i) integers <?fi and prime to m. For the case w = 2-3-5. . .p, where
p is a prime,

lpi-2 Pi J

where K is an integer. Application is made to the finding of a prime
exceeding a given number, and to a generalization of the sieve of Eras-
tosthenes.

E. Ces^ro^^ gave a very simple proof of the known fact that

2 2'

n-00 n^ T

which he expressed in words by saying that 0(n) is asymptotic to 6n/7r^
(not meaning that the limit of 4>{n)/n is G/tt"). On the distinction between
asymptotic mean and median value, see Encyclop^die des sc. math., I,
17 (vol. 3), p. 347.

Ces^ro^^ noted that if F{i, j) is a function of the g. c. d. of i, j, then
Q=SF(i, j) XiXj {i, j = l,..., n) becomes q='Lf{i)yi^ by the substitution
yk = Xk-{-X2k-\-Xsk-\- ■ ■ -, provided F{n) =2/(d), d ranging over the divisors of
n. Since the determinant of the substitution is unity, the discriminants
of Q and q are equal. Hence we have the theorem of Smith.^^ A gen-
eralization is obtained by use of 2F(e„ e^XiXj, where the numbers ei, C2, . . .
include the divisors of each €.

E. Catalan^^ proved that, if d ranges over the divisors of iV = a"6^ . . . ,

E. Busche^° derived at once from Dirichlet's^^ formula the result

S0(x))p(^)+p(^) + ...(=Snn',
j=l \x/ \x /

where p(a) =a — [a]. The case n = n' =n" = . . . leads to

i:4>{x) = {v-\)n^,

where x takes all values for which p{n/x)>p{vn/x). If we take n = l and
add </)(!) = 1, we get (4) for N = v. Next, S0(a;) =rr'5", where x takes all
values for which

yJ±zi^,Q<yyi (y=i,...,.;,'=i,...,.').

r-\-r \xy r r

6«Math. phys. soc. Kasan, 6, 1888, 52-142 (in Russian).

"Comptcs Rendus Paris, 106, 1888, 1651; 107, 1888, 81, 426; Annali di Mat., (2), 16, 1888-9,

178 (discussion with Jensen on terminology).
•8Atti Rcale Accad. Lincei, Rendiconti, 2, 1888, II, 56-61.

"M6m. Soc. Sc. Li^ge, (2), 15, 1888, No. 1, pp. 21-22; Melanges Math., Ill, No. 222, dated 1882.
"Math. Annalen, 31, 1888, 70-74.

Chap. V] EulEr's 0-FuNCTION. 131

For d = n,r' = l,r = v — l, this becomes the former result ; f or r = r ' = 1 , 5 = n,
it becomes 20 (x) =n^, where x takes the values for which p(n/rc)^ 1/2.

H. W. Lloyd Tanner^^ studied the group G of the totitives of n (the
integers <n and prime to n), finding all its subgroups and the simple groups
whose direct product is G.

E. Lucas^^ proved that, in an arithmetical progression of n terms whose
common difference is prime to n, there are (ji{d) terms having with n the g. c. d.
n/d. If, when d ranges over the divisors of n, Xxpid) =n for every integer n,
then (p. 401) \p{n)=(^{n), as proved by using n = l, a, a^,. . ., and n = ah,
a^b, . . . , where a,h,. . . are distinct primes. He gave (pp. 500-1) a proof of
Perott's^^ first formula by induction from N — 1 to N, communicated to him
by J. Hammond. The name " indicateur "of n is given (preface, xv) to
<f){n) [Prouhet^sj.

C. Moreau (cf . Lucas,'^^ 501-3) considered the C{n) circular permutations of
n objects of which a are alike, (3 alike, . . . , X alike. Thus, if a = 2, /3 = 4, the
C(6) = 3 distinct circular permutations are aahbhb, ababbb, abbabb. In general,

^^^^=n^^^^^(a/d)!...(X/d)r

where d ranges over the divisors of the g. c. d. of a, jS, . . . , X. In the
example, d = 1 or 2, and the terms of the sum are 15 and 3.

P. A. MacMahon^^ noted that C(n) = 1 if n = a, so that we have formula
(4). His expression for the number of circular permutations of p things n
at a time is quoted in Chapter III on Fermat's theorem.

A. Berger^^" evaluated S^il k'^%{k). For a = 2 the result is 3nV7rH
\n log n, where X is finite for all values of n.

E. Jablonski'^^ considered rectilinear permutations of indices a, . . ., X,
with the g. c. d. D. Set a = a'D,- • .,\ = \'D, a+ • . .+X = m = m'Z). Then
the number of complete rectilinear permutations of indices a'n, . . . , \'n is

P{n)=- ^'^'''^'

{a'n)\...{\'n)\
The number of complete circular permutations is

where d ranges over the divisors of D. If Q{D/d) is the number of rectilinear
permutations of indices a, . . . , X which can be decomposed into d identical
portions, ^Q(D/d)=P{D). Also

'iProc. London Math. Soc, 20, 1888-9, 63-83.

"Theorie des nombres, 1891, 396-7. The first theorem was proved also by U. Concina, II

Boll, di Matematica, 1913, 9.
"Proc. London Math. Soc, 23, 1891-2, 305-313.
'»«Nova Acta Regiae Soc. Sc. UpsaUensis, (3), 14, 1891, No. 2, 113.
'♦Comptes Rendus Paris, 114, 1892, 904-7; Jour, de Math., (4), 8, 1892, 331-349. He proved

Moreau's'* formula for C{n).

132 History of the Theory of Numbers. [Chap, v

2Q©d'=2pg)/,(d),

where Jt{d) is Jordan's-"" function.

S. Schatunowsky"* proved that 30 is the largest number such that all
smaller numbers relatively prime to it are primes. He employed Tcheby-
chef's^" theorem of Ch. XVIII that, if a> 1, there exists at least one prime
between a and 2a. Cf. Wolfskehl,^^ Landau,^^. 113 Maillet,^^ Bonse/"«
Remak.^^2

E. W. Da\ds''^ used points with integral coordinates ^0 to visualize
and prove (1) and (4).

K. Zsigmondy^^ wrote r, for the greatest integer ^ r/s and proved that,
if a takes those positive integral values ^r which are di\asible by no one
of the given positive integers rii, . . . , n^ which are relatively prime in pairs,

r rn rnn'

2/(a) = S f{k) -S S f{kn) +22 f{knn') -...,

k=l n k=l n, n' k = l

n, n',. . . ranging over the combinations of rii,. . ., n^ taken 1, 2, . . . at a
time. Taking /(A:) = 1, we obtain for the number (f>{r; rii, . . . , nj of integers
^r, which are divisible by no one of ni, . . . , n^, the expression (5) obtained
by Legendre for the case in which the n's are all primes. By induction
from p to p+1, we get

+ 2<^(r^;ni,. ..,n,)-...,

p
r=4>{r] ni, . . . , n,)+ 2 </)(r„<; rii, . . . , n,_i, n,+i, . . . , nj

t=i

+ 2<^(r„„/; riiST^n, n') +

r = 20(r,;ni,.. ., n,),

where c ranges over all combinations of powers ^r of the n's. The last
becomes (4) when ni,. . ., n^ are the different primes di\ading r. These
formulas for r were deduced by him in 1896 as special cases of his inversion
formula (see Ch. XIX).

J. E. Steggair^ evaluated </)(n) by the second method of Crelle.^^

P. Bachmann^^ gave an exposition of the work of Dirichlet,^^ Mertens,"

Halphen^ and Sylvester^^ on the mean of <p{n), and (p. 319) a proof of (5).

L. Goldschmidt^" gave an evaluation of <j){n) by successive steps which

may be combined as follows. Let p be a prime not dividing k. Each of

"Spaczinakis Bote (phys. math.), 14, 1893, No. 159, p. 65; 15, 1893, No. 180, pp. 276-8

(Russian).
"Amer. Jour. Math., 15, 1893, 84.
"Jour, fur Math., Ill, 1893, 344-6.
"Proc. Edinburgh Math. Soc, 12, 1893-4, 23-24.
"Die Anab-tische Zahlentheorie, 1894, 422^30, 481-4.
««Zeitschrift Math. Phys., 39, 1894, 203-4.

Chap. V] EulER's 0-FuNCTION. 133

the <j)(k) integers ^k and prime to k occurs just once among the residues
modulo k of the integers from Ik to {l-{-l)k; taking 1 = 0, 1,. . ., p — l, we
obtain this residue p times. Hence there are p({>{k) numbers ^pk and
prime to k. These include <j){k) multiples of p, whence 4){pk) = {p — l)(p{k).
For, if r is one of the above residues, then r, r+k,. . ., r-{-{p — l)k form a
complete set of residues modulo p and hence include a single multiple of p.
Hence

</)(a6c...) = (a-l)(6-l)(c-l)...,

if a, b, c, . . . are distinct primes. Next, for n = a^h^ . . . , we use the sets of
numbers from lab. . .to (l-]-l)ab. . ., for Z = 0, 1,. . ., a°-~^b^~^ . . . — 1.

Borel and Drach^^ noted that the period of the least residues of 0, a,
2a,... modulo N, contains N/8 terms, if d is the g. c. d. of a, iV; conversely,
if d is any divisor of N, there exist integers such that the period has d terms.
Taking a = 0, 1,. . ., iV — 1, we get (4).

H. Weber ^^ defined 0(n) to be the number of primitive nth roots of
unity. If a is a primitive ath root of unity and /3 a primitive 6th root, and
if a, b are relatively prime, a/3 is a primitive a6th root of unity and all of
the latter are found in this way. Hence 0(a6) =</)(a)0(6). This is also
proved for relatively prime divisors a, 6 of n — 1, where n is a prime, by use
of integers a and jS belonging to the exponents a and b respectively, modulo
n, whence a^ belongs to the exponent ab.

K. Th. Vahlen^^ proved that, if la.^in) is the number of irreducible frac-
tions between the limits a and /3, a>j8^0, with the denominator n,

S/„.,(d) = [(a-^)n], ij~~^h,,{k)=i[{a-m],

where d ranges over the divisors of n. For /3 = 0, the first was given by
Laguerre.^^ Since /i,o(^)=<^(^), these formulas include (4) of Gauss and
that by Dirichlet.2i

J. J. Sylvester^ corrected his^^ first formula to read

k^[k\ = 2Ui]H[i]t ^^U), r[n]=0(l)+. . .+c^([n]),
and proved it. By the usual formula for reversion,

A. P. Minin^^ solved ^(f){m)=R for m when R has certain values. The
equation determines the number of regular star polygons of m sides.
Fr. RogeP® gave the formula of Dirichlet.^^

*'Introd. thdorie des nombres, 1895, 23.

«Lehrbuch der Algebra, I, 1895, 412, 429; ed. 2, 1898, 456, 470.
"Zeitschrift Math. Phys., 40, 1895, 126-7.

"Messenger Math., 27, 1897-8, 1-5; Coll. Math. Papers, 4, 738-742.

"Report of Phys. Sec. Roy. Soc. of Friends of Nat. Sc, Anthropology, etc. (in Russian), Mos-
cow, 9, 1897, 30-33. Cf. Hammond."^
«»Educat. Times, 66, 1897, 62.

134 History of the Theory of Numbers. [Chap, v

RogeP^ considered the number of integers v<n such that v and n are
not both di\'isible by the rth power of a prime. Also the number when
each prime factor common to v and n occurs in them exactly to the rth power.

I. T. Kaplan published at Odessa in 1897 a pamphlet in Russian on the
distribution of the numbers relatively prime to a given number.

M. Bauer^^ proved that, for x prime to in, kx-\-l represents

\p{m) 4>{d^d2)

<j)

integers relatively prime to m and incongruent modulo m, where di is the
g. c. d. {k, m) of k, m, and c?2= (/, m), {di, do) = 1, w^hile

^W=0Wn{i-^}

is the number of incongruent integers prime to m = pi^ . . . p/* which are
represented by kx+l when k, I, x are prime to 7n. Of those integers,
\p{m)/\l/{pi. . .pr) are di\'isible only by the special prime factors Pi, . . ., Pr
of m.

J. de Vries^^" proved the first formula of Dirichlet's.^^
C. Moreau^^ evaluated 4){n) by the method of Grunert.^^
E. Landau^° proved that

„=i<^(n) 27r^ \ *= pp2_p+iy

where e is of the order of magnitude of x~^ log x, C is Euler's constant, and
f is Riemann's ^-function.

P. WolfskehP^ proved by Tchebychef's theorem that the 0(n) integers
<n and prime to n are all primes only when n = 1, 2, 3, 4, 6, 8, 12, 18, 24, 30,
[Schatunowsky.'°]

E. Landau^^ gave a proof, without the use of Tchebychef's theorem, by
finding a lower limit to the number of integers k ha\dng no square factor
>1, where t^k>Dt/S.

E. Maillet,^^ by use of Tchebychef's theorem, proved the same result
and the generaUzation : Given any integer r, there exist only a finite number
of integers N such that the <t>{N) integers <A^ and relatively prime to N
contain at most r equal or distinct prime factors.

Alois Pichler^'* noted that (}>(x)=n has no solution if n is odd and >1;
while (i)(x) =2" has the solutions x = 2''bc. . . (a = 0, 1, . . ., n + 1) if

«^Sitzungsber. Bohm. GeseU., Prag, 1897; 1900, No. 30.
"Math. Natur. Berichte aua Ungam, 15, 1897, 41-6.
""K. Akad. Wetenschappen te Amsterdam. Verslagen, 5, 1897, 222.
"Nouv. Ann. Math., (3), 17, 1898, 293-5. '
»»G6ttingen Nachrichten, 1900, 184.

"L'interm^diaire des math., 7, 1900, 253-4; Math. Ann., 54, 1901, 503-4.
"Archiv Math. Phys., (3), 1, 1901, 138-142.
»»L'interm6diaire des math., 7, 1900, 254.

"Ueber die Auflosimg der 01. <p{x) =n. . ., Jahres-Bericht Maximilians-Gymn. in Wien, 1900-1,
3-17.

Chap. V] EulEK's 0-FuNCTION. 135

6 = 2^^+1, c = 22''+l,...

are distinct primes and 2^+2"^+. . . =n or n — a+1 according as a = 0 or
a>0. When g- is a prime >3, <f){x) = 2q'' is impossible if p = 2q^-\-l is not
prime; while if p is prime it has the two solutions p, 2p. If g = 3 and p is
prime, it has the additional solutions 3"+\ 2-3''"^^ Next, 4>{x)=2''q is
impossible if no one of p^ = 2''~''q-\-l{v = 0, 1,. . ., n — 1) is prime and q is
not a prime of the form 2*+l, s = 2^^n; but if q is such a prime or if at
least one p^ is prime, the equation has solutions of the respective forms bq^,
where (/)(6) =2""*; ap„ where 0(o) =2". Finally, (f>{x)=2qr has no solution
if p = 2gr+l is not prime and r9^2q-\-l. If p is a prime, but r9^2q-{-l, the
two solutions are p, 2p. If p is not prime, but r = 2g+l, the two solutions
are r^, 2r^. If p is prime and r = 2g-|-l, all four solutions occur. There is
a table of the values n<200 for which (f){x)=n has solutions.

L. Kronecker®^ considered two fractions with the denominator m as
equivalent if their numerators are congruent modulo m. The number of
non-equivalent reduced fractions with the denominator m is therefore 4){m).
If m = m'm", where m' , m" are relatively prime, each reduced fraction r/m
can be expressed in a single way as a sum of two reduced partial fractions
r' /m', r' /m". Conversely, if the latter are reduced fractions, their sum
r/m is reduced. Hence 0(m) =</)(m')</)(m"). The latter is also derived
(pp. 245-6, added by Hensel) from (4), which is proved (pp. 243-4) by
considering the g. c. d. of n with any integer ^n, and also (pp. 266-7) by
use of infinite series and products. Proof is given (pp. 300-1) of (5). The
Gaussian median value (p. 334) of (f>{n)/n is Q/w^ with an error whose order
of magnitude is l/\/n, provided we take as the auxiliary number of values
of 4>{n)/n a value of the order of magnitude ^yn log^ n.

E. B. Elliott^^ considered monomials n = p'^q^. . . in the independent
variables p,q,.... In the expansion of n(l — l/p)"'(l — l/g)"* . . . , the aggre-
gate of those monomial terms whose exponents are all ^0 is denoted by
Fm{n). Define iJi{p'q\ . .) to be zero if any one of r, s, . . . exceeds 1, but to
be ( — 1)' if no one of them exceeds 1, and t of them equal 1. Then

(7) F^_i(n) =Si^,,(d), F^^,{n) =Sm Q) F^((i),

where d ranges over the monomials pV- • • with O^a^a, 0^/3^?),....
Henceforth, let p, q,... be distinct primes. Then Fi{n)=(j){n), while
F_i(n) is the sum o-(n) of the divisors of n. In (7), d now ranges over all
the divisors of n, and ai(/c) is Merten's function [Inversion]. For m = 0, (72)
gives the usual expression for </)(n), while (7i) defines o-(n). For m = l, (7i)
becomes (4).

If T''^\n) ^T(n) is the number of divisors d of n, write

r(2)(n)=ST(d),. . ., T(^>(n)=ST^^-i>(d).

'^Vorlesungen iiber Zahlentheorie, I, 1901, 125-6.
»«Proc. London Math. Soc, 34, 1901, 3-15.

136 History of the Theory of Numbers. [Chap, v

Then

Generalizing /x(s), let )u-*^(s) be zero if the expansion of the product
n(l— p)*", extended over all primes p, does not contain a term equal to s,
but let it equal the coefficient of s if s occurs in the expansion. Then

i?,(n)=SdM'"Q)

The 7i-rowed determinant in which the element in the rth row and sth
column is F„_i(5), where 5 is the g. c. d. of r, s, is proved equal to F^(l)
F^(2) . . .Fm{n), a generaUzation of Smith's^^ theorem. Finally,

isf.,,Q)f_.(d)=siF,(d),

the right member being T{n), 20(c?)/c?, lla{d)/d for r = 0, 1, —1.

G. Landsberg^^" gave a simple proof of Moreau's"^ formula for the
number of circular permutations.

L. Carlini^^ proved Dirichlet's^^ formula by noting that

(8) n(x''-l)=0

has unity as an n-f old root, while a root 7^ 1 of x'' — 1 is a root of [n/h] factors
x"* — 1. Hence the 4){h) primitive roots of x^ = \ furnish <l>{h)[n/h] roots
of (8).

M. Lerch^^ found the number N of positive integers '^m which have no
one of the divisors a, 6, . . . , k, I, the latter being relatively prime in pairs
and ha\'ing m as their product. Let F{x) = 1 or 0, according as x is frac-
tional or integral. Let L = ab. . .k. Then [Dirichlet^^]

^^m(Z-l)^

,!/©-©-(-■) (-i)

L
E. Landau^^ proved that the inferior limit for a:= 00 of

-<f>{x) log. log, X

X

is e~^, where C is Euler's constant. Hence <^(j) is comprised between this
inferior limit and the maximum x — 1.

R. Occhipinti^°° proved that, if aj is an nth root of unity, and if c?,i, • ■ • ,
dat are the divisors of i,

n|s<^(di,)+a,S<^(d2i)+. . .+a/-4V(0| = i(-l)"-'n(n+l)n"-2.

j-lU-l i-l i-l J

••"Archiv Math. Phys., (3), 3, 1902, 152-4. "Periodico di Mat., 17, 1902, 329.

"Prag Sitzungsber., 1903, II. "Archiv Math. Phys., (3), 5, 1903, 86-91.

"«Periodico di Mat., 19, 1904, 93. Handbuch,"' I, 217-9.

Chap. V]

Euler's 0-Function.

137

G. A. Miller^"^ proved (4) by noting that in a cyclic group G of order N
there is a single cyclic subgroup of order d, a divisor of N, and it contains
0((i) operators of order d, while the order of any operator of G is a divisor
of N. Thus (4) states merely that the order of G equals the sum of the
numbers of the operators of the various possible orders. Next, (1) follows
from an enumeration of the operators of highest period AB in a cyclic group
of order AB, which is the direct product of its cyclic subgroups of orders
A and B. Finally, if p is a prime, all the subgroups of a cyclic group of
order p" are contained in its subgroup of order p"~\ whence <^(p") = p" — p"~^

G. A. Miller^°^ proved the last three theorems and the fact that 0(0 is
even if Z>2 by means of the properties of the abelian group whose elements
are the integers <m which have with m a g. c. d. equal to k.

K. P. Nordlund^"^ proved 4){mn ...) = (m — l)(n — 1)..., where m, n,. . .
are distinct primes, by writing down the multiples <mnp of m, the multi-
ples of mn, etc., whence the number of integers Kmnp and not prime to it
is mnp — l — {m — l){n — l){p — l),

E. Busche^*^ treated geometrically systems (td) of four integers such

that ad — hc>0, evaluated the number $(aS) of systems incongruent modulo
S and prime to S, and generalized (4) to 2$(*S).

L. Orlando^°^ showed that 0(m) is determined by (4) [Lucas''^].

H. Bonse^°^ proved Maillet's^^ theorem for r = l, 2, 3 without using
•■Tcheby chef's theorem. His lemma was generalized by T. Suzuki. ^°^"

J. Sommer^^^ gave without reference Crelle's^ final evaluation of (/)(n).

R. D. CarmichaeP*'^ proved that if n is such that (l){x)=n is solvable
there are at least two solutions x. He found solutions of </)(x) = 2" [in accord
with Pichler^^] and proved that there are just n+2 solutions (a single one
being odd) when n^31 and just 33 solutions when 32^ n^ 255. All the
solutions of <^(x) = 4n — 2> 2 are of the form p", 2p", where p is a prime of the
form 4s — 1 ; for example, if n = 5, the solutions are 19, 27 and their doubles.

CarmichaeP°® gave a table showing every value of m for which 0(m)
has any given value ^ 1000.

A. Ranum^^^" would solve 4>{x) = n by resolving n in every possible way
into factors no, ., n^, capable of being taken as the values of 0(2*"), 4>{pi'),
. . ., 0(pA)) where 2, pi, . . ., p, are distinct primes. Then 2'^pi"'. . .p^^'r is
a value of x.

CarmichaeP^" gave a method of solving (j>(x)=a, based on the testing
of the equation for each factor x of a definite function of a.

M. Fekete^^^ considered the determinant pkn obtained by deleting the
last row and last column of Sylvester's eliminant for a;''' — 1 = 0 and a;** — 1 = 0

"lAmer. Math. Monthly, 12, 1905, 41-43.
"'Amer. Jour. Math., 27, 1905, 315.
"'Nyt Tidsskrift for Mat., 16A, 1905, 15-29.
iMJour. fiir Math., 131, 1906, 113-135.
"»Periodico di Mat., 22, 1907, 134-6.
iwArchiv Math. Phya., (3), 12, 1907, 292-5.
i^^Tohoku Math. Jour., 3, 1913, 83-6.
"'Vorlesungen liber Zahlentheorie, 1907, 5.

"SBull. Amer. Math. Soc, 13, 1907, 241-3.

"»Amer. Jour. Math., 30, 1908, 394-400.

lo'^^Trans. Amer. Math. Soc, 9, 1908, 193-4.

"«BuU. Amer. Math. Soc, 15, 1909, 223.

"iMath. 6s Phys. Lapok (Math. Phys. Soc),
Budapest, 18, 1909, 349-370. German
transl., Math. Naturwiss. Berichte aus
Ungam, 26, 1913 (1908), 196.

138 History of the Theory of Numbers. [Chap, v

{k<n). Thus |p;tn| = 1 or 0 according as k and n are relatively prime or not.
Hence

n n

(t>{n) = 2 \pkn\, (t>i(n) = 2 fc|pt„|,

A=l k=l

where <i>i{n) is the sum of the integers ^n and prime to n.

R. Remak^^- proved Maillet's^^ theorem without using Tehebychef's.

E. Landau^^^ proved (5), Wolfskehl's^^ theorem and Maillet's^^ generali-
zation.

C. Orlandi^" proved that, if x ranges over all the positive integers for
wliich [m/x] is odd, then 20(x) = (?w/2)'^ for 7fi even (Cesaro, p. 144 of this
History), while 20 (x) = k^ for m = 2k — l.

A. Axer^^° considered the system (P) of all integers relatively prime to
the product P of a finite number of given primes and obtained formulas
and asymptotic theorems concerning the number of integers ^x of (P)
which are prime to x. Application is made to the probability that two
numbers ^ n of (P) are relatively prime and to the asymptotic values of the
number (i) of positive irreducible fractions with numerator and denominator
in (P) and ^n and {ii) of regular continued fractions representing positive
fractions m (P) with numerator and denominator S n.

G. A. ]Miller^^^ defined the order of a modulo m to be the least positive
integer h such that ab=0 (mod m). If p" is the highest power of a prime
p dividing vi, the numbers ^7n whose orders are powers of p are km/p"
(k = l, 2,. . ., p"). Hence l^kim/p-'i {ki = \,. . ., p-'i) form a complete set of
residues modulo 7?i=Ilpi'i. If the orders of two integers are relatively
prime, the order of their sum is congruent modulo 77i to the product of
their orders. But the number of integers ^m whose orders equal m is
(t>{7n). Hence (/)(np°) =n0(p°). Since all numbers ^m whose orders
divide d, a di\'isor of 7n, are multiples of 7n/d, there are exactly d numbers
^m whose orders di\ide d, and (f){d) of them are of order d. Hence
7n = 'E4>{d).

S. Composto^^^ employed distinct primes 7n, n, r, and the v=<t>{77in)
integers P\,...,p^ prime to Tnn and ^ mn, and proved that

Pi, Pi+7nn, pi+2mn, . . . , p,+(r- l)wn {i = l,. . .,v)

include all and only the numbers rpi,. . ., rp, and the numbers not exceeding
and prime to 7nnr. Hence 4>{vmr)=4>{m7i)-{r — \). A like theorem is
proved for two primes and stated for any number of primes. [The proof is
essentially Euler's^ proof of (1) for the case in which J5 is a prime not divid-
ing a product A of distinct primes.] Next, if d is a prime factor of 7i, the
integers not exceeding and prime to dn are the numbers ^ n and prime to n,
together with the integers obtained by adding to each of them n, 2n, . . . ,

"2.\rchiv Math. Phys., (3), 15, 1909, 186-193.

i^Handbuch. . .VerteUung der Primzahlen, I, 1909, 67-9, 229-234.

"♦Periodico di Mat., 24, 1909, 17&-8.

"'Monatshefte Math. Phys., 22, 1911, 3-25.

"«.\mer. Math. Monthly, 18, 1911, 204-9.

"'II Boll, di Matematica Gior. Sc.-Didat., 11, 1912, 12-33.

Chap. V] EulEr's 0-FunCTION. 139

(d — l)n; whence 4>{dn) = d^{n) . Finally, let Pi, ..., Py be the v = (f){n)
integers <n and prime to n. Then pi-\-kn (^ = l, . . .,v; k = 0, 1, . . .) give
all integers prime to n; let Ph{n) denote the hth one of them arranged in
order of magnitude. Then

P,Xn)=kn-l (k^l), P,,+M=kn+pr {l^r^v-l, k^O).

If h = kv-\-r, r<v, the sum of the first h numbers prime to n is

where pi, . . . , p^ are the first r integers <n and prime to n.

K. HenseP^^ evaluated <^(n) by the first remark of Crelle.^'^

J. G. van der Corput and J. C. Kuyver^^^ proved that the number
/(a/4) of integers ^ a/4 and prime to a is N = \aJl{l — \/p) if a has a prime
factor 4m+l, where p ranges over the distinct prime factors of a; but is
N — 2^~^ if a is a product of powers of k prime factors all of the form 4m — 1.
Also /(a/6) is evaluated.

U. Scarpis^^'^ noted that 0(p" — 1) is divisible by n if p is a prime.

Several writers^^^ discussed the solution of 4>{x)=4){y), where x, y are
powers of primes. SeveraP^^ proved that (f){xy)>4>{x)4>{y) if x, y have a
common factor.

J. Hammond^^^ proved that there are ^^(n) — 1 regular star n-gons.

H. Hancock^"^ denoted by ^{i, k) the number of triples {i, k, 1), {i, k, 2),
. . . , {i, k, i) whose g. c. d. is unity. Let i = iid, k = kid, where ii, ki are
relatively prime. Then ^{i, k)=ii(i>{d), $(/c, i)=ki(j}(d).

A. Fleck^^^ considered the function, of m^Hp",

<p,{m) = n|<^(p«) - (J)c/>(p"-^) +...+(- i)°(^y (p^-")}.

Thus (f)o{'m) =4){'m), <^_i(m) = m, <^_2(w) is the sum of the divisors of m. Also
S 4>k{d)=<i>k-i{m), (f>kimn)=(l)k{ni)(t)k{n),

d:m

if m, n are relatively prime. For f (s) =2m~*,

^ (f)k-i{m) ^ 4>k{m)

0.(p)=p-CI^), 0.(p^)=p^-(^l>+Ct')' ■•'

</).(p'+'+o=p''(p-l)'^'.

"sZahlentheorie, 1913, 97.

"^Wiskundige Opgaven, 11, 1912-14, 483-8.

i^'oPeriodico di Mat., 29, 1913, 138.

i2iAmer. Math. Monthly, 20, 1913, 227-8 (incomplete); 309-10.

li'^Math. Quest. Educat. Times, 24, 1913, 72, 106.

^^'Ibid., 25, 1914, 69-70.

i^^Comptes Rendus Paris, 158, 1914, 469-470.

"^Sitzungsber. Berlin Math. Gesell., 13, 1914, 161-9.

140 History of the Theory of Numbers. [Chap, v

E. Cahen^^^ gave F. Arndt's^^ proof without reference.

A. Cunningham^" tabulated all solutions N of 0(iV)=2' for r = 4, 6, 8,
9, 10, 11, 12, 16, each solution being a product of a power of 2 by distinct
primes 22"+ 1.

J. Hanmiond^-^ noted that, if 'Zf{k/n)=F{7i) or <l>(n), according as the
summation extends over all positive integers k from 1 to n or only over
such of them as are prime to n, then Z$(d)=F(n). This becomes (4)
when /is constant.

R. Ratat^29 ^oted that 0(n) = 0(n + l) for n= 1, 3, 15, 104. For n<125,
2n7^2, 4, 16, 104, he verified that (/)(2n=t l)>0(2n).

R. Goormaghtigh^^o ^^^^^ ^j^j^^ 0(^^) = <^(^i_|_l) also for n= 164, 194, 255

and 495. He gave very special results on the solution of (f){x) = 2a.

Formulas involving cf) are cited under Lipschitz,'''°' ^^ Cesaro,^^ Ham-
mond,^" and Knopp^^^ of Ch. X, Hammond^ of Ch. XI, and RogeP« of
Ch. XVIII. Cunningham^^ of Ch. VII gave the factors of (t>{f). Dede-
kind^^ of Ch. VIII generalized ^ to a double modulus. Minin^^° of Ch.
X solved 0(iV)=r(A^).

Sum 0fc(n) of the A:th Powers of the Integers ^n and Prime to n.

A. Cauchy^^^ noted that (piin) is divisible by n if n>2, since the integers
<n and prime to n may be paired so that the sum of the two of any pair is n.

A. L. Crelle^^ (p. 80, p. 84) noted that (^i(n) = |n<^(n). The proof
follows from the remark by Cauchy.

A. Thacker^^*^ defined (f)k{n) and noted that it reduces for k = 0 to Euler's
<i>{n). Set St(2) = l'"-|-2^+ . . .+2^n = a°6V. . ., where a, 6, . . . are distinct
primes. By deleting the multiples of a, then the remaining multiples of
b, etc., he proved that

Mn)=sM -2a^s.(^) +2 aVs,(^) - S ^a*feVs,(^) + . . . ,

where the summation indices range over the combinations of a, 5, c, . . . one,
two, ... at a time. In the second paper, he proved Bernoulli's^^"" formula

where Bi, Bz,... are the Bernoullian numbers. Then, by substitution,
^^(^)=^n(l-i)+§(J)5,n^-^n(l-a)-i(3)53n*-^n(l-a^)

i^TWorie des nombres, I, 1914, 393.

i"Math. Quest. Educ. Times, 27, 1915, 103-6.

128/bid., 29, 1916, 53.

i"L'interm(5diaire des math., 24, 1917, 101-2.

"»/6ui., 25, 1918, 42-4.

"'M6m. Ac. Sc. de I'Institut de France, 17, 1840, 565; Oeuvres, (1), 3, 272.

"ojour. fur Math., 40, 1850, 89-92; Cambridge and Dublin Math. Jour., 5, 1850, 243. Repro-
duced, with errors as to signs, by Zerr, Amer. Math. Monthly, 5, 1898, 93-5. Cf. E.
Prouhet, Xouv. Ann. Math., 10, 1851, 324-330.

"""Jacques Bernoulli, Are conjectandi, 1713, 95-7.

Chap. V] GENERALIZATIONS OF EuLER's 0-FuNCTION. 141

wheren(l-aO denotes {l-a^){l-h'). . ..

J. Binet^" wrote Vif ■ ■> Vn for the integers <iV and prime to N^p^q". . ..
Then, if B^, —B^, B^,... are the BernouUian numbers 1/6. 1/30, 1/42, . . .,

andP,= (l-p^)(l-g'')...,

for X sufficiently small to insure convergence. Expanding each member into
negative powers of x and comparing coefficients, we get

n =277/ = P_,N, 2Sr7i = P_,N\ SXrjf = P_,N^+SB,P,N,

^n,^ = P_,N^+QB,P,N^.. .

the first being equivalent to the usual formula for 0(iV). The general law
can be represented symbolically by

givr'=^\{N+Bpy-h{N-Bpy\,

where, after expanding the binomials, we are to replace N"/{BP) by P^iN"
and any other term {BPY^~'^ by B2h-\P2h-\- It is easily shown that, if k is
odd, Hit]'' is divisible by N.

Silva^^ used his symbolic formula, taking S to be the sum of 1, . . ., n,
whence S{a) is the sum §n(l+n/A) of the multiples ^n of A. Thus
^i(^) = 2^(^) • This proof of Crelle's result is thus like that by Brennecke.^"

W. Brennecke^^^ proved Crelle's result by means of

H-...+n-la(l+2+...+^)+6(l+...+^) + ...t

+ ]4+...+;J + . ..! + ....

Set )Li = 0(n) , a = ahc .... He proved that

<i>^{n)=^}xn'-^\aixn^-^n{\-a^){\-h^) . . .,

the signs being + or — according as the number of the distinct prime
factors a, 6, . . . of n is even or odd.

•"Comptes Rendus Paris, 32, 1851, 918-921.
"^Programm Realschule, Posen, 1855, §§5-6.

142 History of the Theory of Numbers. [Chap, v

G. Oltramare^^ obtained for the sum, sum of squares, sum of cubes, and
sum of biquadrates, of the integers <7na and relatively prime to a the
respective values

^m~a<}>{a), JmV0(a) + (-l)»— a0(a,), ll

o

imV</>(«) + (-l)"^a2<A(ai),

Ttl 111

6 z-O'O

where a is the number and Oi the product of the distinct prime factors
ju, I', . . . of a, while ^(aO = (ju^ — l)(j/^ — 1) . . .. The number of integers <n
which are prime to a is 4>{a)n/a.

J. Liou\'ille^^ stated that Gauss' proof of S0(d) =iV may be extended to
the generalization

2QWc?) = l*+2*+...+iV*,

where d ranges over the di\'isors of N. He remarked that Binet's^" results
are readily proved in various ways. Also,

e);3w={z>wf.

N. V. Bougaief^^^ stated that, if ^(n) is the number of distinct prime
factors of n>\, and ^i(n) is their product,

also a result quoted below with Gegenbauer's^"° generalization.

August BUnd^^^ reproduced without reference the formulas and proofs
by Thacker,^^° and gave

0,(m)=w'</)o(7n)-^^^w'-Vi(/7O + ('2)^«''-'<A2W- • . . +(-l)'<^.(^0.

E. Lucas^^^ indicated a proof that 7?<^„_i(x) is given symbolically by
{x+QY-Q\ where, if n = a°6^ . ., 0, = 5,(l-a'-')(l-5'-0 - • •• Thus, if
IT is the product of the negatives of the primes a, b, . . . ,

2</)i(x) =x4>{x), 3<t>2{x) =(j>{x) (x~ + hA , 403Ct) =.T(/)(.T)(x2+7r).

'"Mdmoires de I'lnstitut Nat. Gr^nevois, 4, 1856, 1-10.

""Comptea Rendus Paris, 44, 1857, 753-4; Jour, de Math., (2), 2, 1857, 393-6.

i"Nouv. Ann. Math., (2), 13, 1874, 381-3; Bull. Sc. Math. Astr., 10, I, 1876, 18.

'**Ueber die Potenzsummen der iinter einer Zahl ?« Uegenden und zu ihr relativ primen Zahlen,

Diss., Bonn, 1876, 37 pp.
i^^Nouv. Ann. Math., (2), 16, 1877, 159; Throne des nombres, 1891, 394.

Chap. V] GENERALIZATIONS OF EuLER's 0-FuNCTION. 143

Several ^^^^ found expressions for 0„=<^„(iV) and proved that

</>ox'»+n</)ia;"-i+i7i(n- 1) (/)2a;"-2+ . . . +<^„= 0 (n odd)

has the root —4>\/4>q, while the remaining roots can be paired so that the
sum of the two of any pair is — 20i/(/)o. If n=3 the roots are in arith-
metical progression.

H. Postula^^^ proved Crelle's result by the long method of deleting
multiples, used by Brennecke.^^^ Catalan {ibid., pp. 208-9) gave Crelle's
short proof.

Mennesson^^^ stated that, if q is any odd number,

<^» = *0(^'+') (modg),

and (Ex.366) that the sum of the products (/)(n) — 1 at a time of the integers
^n and prime to n is a multiple of n.

E. Cesaro^^° proved the generalization: The sum rprn of the products m
at a time of the integers a, ^,. . .^N and prime to N is divisible by iV if m
is odd. For by replacing a by iV— a, /3 by A^"— j8, . . . and expanding.

'^^-&^Ht-\y-Mt'-2y

¥2-...

where 0=0(iV). Also (l>m{N) is divisible by iV if m is odd.

F. de Rocquigny^^^ proved Crelle's result. Later, he"^ employed con-
centric circles of radii 1, 2, 3, . . . and marked the numbers {m — l)N-}-l,
(m — l)N-\-2, . . ., mN at points dividing the circle of radius m into A'' equal
parts. The lines joining the center to the 0(iV) points on the unit circle,
marked by the numbers <N and prime to N, meet the various circles in
points marked by all the numbers prime to N. He stated that the sum
of the 4>{N) numbers prime to N appearing on the circle of radius m is
|(2m — l)0(iV^), and [the equivalent result] that the sum of the numbers
prime to N from 0 to mN is ^'m^(i>{N^). He later recurred to the subject
{HUd., 54, 1881, 160).

A. Minine^®^ noted that, if P>N> 1 and k is the remainder obtained by
dividing P by N, the sum s{N, P) of the integers <P and prime to N may
be computed by use of

s{N, mN+k)=s{N, k)+^4>{N')+mN4>{N)„

where (Minine^O <i>{N)k is the number of integers ^k prime to N.

*A. Minine^^^ considered the number and sum of all the integers < P
which are prime to N [Legendre's (5) and Minine^*^^].

i"«Matli. Quest. Educ. Times, 28, 1878, 45-7, 103-5.

i"Nouv. Corresp. Math., 4, 1878, 204-7. Likewise, R. A. Harris, Math. Mag., 2, 1904, 272.

^^lUd., p. 302.

i6«76id., 5, 1879, 56-59.

"iLes Mondes, Revue Hebdom. des Sciences, 51, 1880, 335-6.

i62/6id., 52, 1880, 516-9.

i"/6id., 53, 1880, 526-9.

"^Nouveaux theoremes de la th^orie des nombres, Moscow, 1881.

144 History of the Theory of Numbers. [Chap, v

A. Minine^^ investigated the numbers N which divide the sum of all
the integers < N and prime to N.

E. Cesaro^^^ proposed his theorems^®^ as exercises. Proofs, by associa-
ting a with N — a, etc., were given by Moret-Blanc (3, 1884, 483-4).

Ces^ro" (p. 82) proved the formula of Liouville.^" Writing (pp. 158-9)
<f)„ for </),„(A0 and expanding 0„=2(iV— a)"*, where a, /3, . . . are the integers
^ A^ and prime to A'^, we get

whence <^^ is di\'isible by N if m is odd, but not if m is even. This is e\'ident
(p. 257) since aJ^ -{- {N — a)"" is di\isible by a+A'' — a if m is odd. The above
formula gives A'" = (1 — A)"*, symboUcally, where

" 4> AT-"

is the arithmetic mean of the mth powers of a/N, ^/N, .... The mean
value of <j)m{N) is 6A„A"'"+V'''"^- He reproduced (pp. 161-2) an earHer for-
mula,^^° which shows that B"' = {l-B)'", symbolically, if B^ is the arith-
metic mean of the products of a/N, ^/N, . . . taken m at a time. We have
(p. 165) the approximation

X x"*"^^ 6

2 <f)m(j) = 7 — rrr} — r^ * ~2>
y=i (7M+l)(m-|-2) tT

whence (p. 261) the mean of (t>^{N) is 6A''"+7(m+l)7r2.
Proof is given (pp. 255-6) of Thacker's^^° formula

*-«'"'"'*'::;"'*'""-iiiij.cr)'-»-""'"'

where

UN)=^d'-'f^(d)=Il{l-u^-'),

d ranging over the divisors of A^, and u over the prime divisors of N. Here
nix) is Merten's function (Ch. XIX). It is proved (pp. 258-9) that

2d^-Vp(^ = 1, 2^V.(^ =2dV,-.(rf),

the first characterizing the function \pp{N), and reducing to (4) for p = 0.
If a ranges over the integers for which [2n/a] is odd, then (p. 293)

exactly if 7?7 = 0, 1, 2, 3, approximately if m>3, where A^, is the excess of the
sum of the inverses of 1,. . ., n over that of n + l, . . . , 2n. In particular,

20(a) =nl

'"Math. Soc. Moscow (in Russian), 10, 1882-3, 87-101.
»«Nouv. Ann. Math., (3), 2, 1883, 288.

Chap. V] GENERALIZATIONS OF EuLER's </)-FuNCTION. 145

P. Nazimov^" (Nasimof) noted that, when x ranges over the integers
^m and prime to n, the sum of the values taken by any function /(x) equals

\mld\

7:ix{d)Xf{dx),

d 1=1

where d ranges over all divisors of n. The case f{x) = 1 yields Legendre's
formula (5) . The case/(a;) = xyields a result equivalent to that of Minine.^^^"'*
A generalization was given by Zsigmondy'^'^ and Gegenbauer.^'^^

E. Cesaro^^^ noted that, if A^ is the arithmetic mean of the mth powers
of the integers ^ N and prime to N, and B^ that of their products m at a
time, we have the symbolic relations

Cesaro^^^ proved Thacker's^^'^ formula expressed as

the last being symboHc, where f^ is a function such that l^^,,{d)='n}~^, d
ranging over the divisors of n. By inversion

n(n)=2M©<i'-'=;^n (!-»-'),

where u ranges over the distinct prime factors of n.
L. Gegenbauer^'^° proved that, if j/= yln ,

x-l n=lL3; J ,-1

For the case /c = 0, p = 2, this becomes Bougaief 's^^^ formula
ig2{x)=i\^^<i>{x), v = [Vn].

C. Leudesdorf^'^^ considered for fx odd the sum i/'^(iV) of the inverses of
the juth powers of the integers < N and prime to N. Then

^|^,{N)=^kN'-hfiN^P,+,iN),

where k is an integer. Thus, if N = p^q, where q is not divisible by the
prime p>3, »/'^(A^) is divisible by p^' unless ju is prime to p, and )U+1 is
divisible by p — 1; for example, \{/^{p) is divisible by p^. If p = 3, ^l/^iN)
is divisible by p^' if fx is an odd multiple of 3. If p = 2, it is divisible by
2^'~^ except when q = l.

Cesaro"^ inverted his" symbolic form of Thacker's formula for <l)m{N)
in terms of xf/'s and obtained

nB,rPp{n) = {<f>-nBy.

i"Matem. Sbomik (Math. Soc. Moscow), 11, 1883-4, 603-10 (Russian).

"'Mathesis, 5, 1885, 81.

"'Giomale di Mat., 23, 1885, 172-4.

""Sitzungsber. Ak. Wiss. Wien (Math.), 95, II, 1887, 219-224.

i"Proc. London Math. Soc, 20, 1889, 199-212.

"Teriodico di Mat., 7, 1892, 3-6. See p. 144 of this history.

s

146 History of the Theory of Numbers. [Chap, v

Hence if a ranges over the integers ^ n and prime to n,
Z(a — nBy = 0 or a multiple of mpp
according as p is odd or even. By this recursion formula,

L. Gegenbauer"^ gave a formula including those of Nazimov^^^ and
Zsigmondy." For any functions xid), Xiid) , f i^i, ■ ■ ■ , x,),

m /^\ /^\1 [m/d]

f{KXi,. . ., /cx,)2x(5)xiM =^x(d)xA^) ^ 2 ^ fidKX^,. . ., dKX,),

where d ranges over all divisors of n which have some definite property P,
while 5 ranges over those common divisors of n, Xi,..., x, which have
property P. Various special choices are made for x> Xi> / and P. For
instance, property P may be that d is an exact pth power, whence, if p = 1,
d is any divisor of n. The special results obtained relate mainly to new
number-theoretic functions without great interest and suggested apparently
by the topic in hand.

T. del Beccaro^'^ noted that (t>k{n) is divisible by n if A; is odd [Binet^^^].
When n is a power of 2,

l^+2*+...4-(n-l)* = Oor0(n) (modn),

according as k is odd or even. His proof of (1) is due to Euler.

J. W. L. Glaisher^^^ proved that, if a, h,. . . are any divisors of x such
that their product is also a divisor, the sum of the nth. powers of the integers
< X and not divisible by a or 6, . . . , is

where s is the number of the divisors a, 6, ... , and

li a,h,. . . are all the prime factors of x, this result becomes Thacker's.^^"
N. Nielsen^^^ proved by induction on y that the sum of the nth powers
of the positive integers <mM and prime to M = pi^. . .ply is

"'""'^'^W+(-i)-'f'^-^'"' C^+iV (™m)"--' n (P---1).

n+l «=in+l \ zs y ,=i

The case m= 1 gives Thacker's^^° result. That result shows {ihid., p. 179)
that 02n(w) and <^2n+i(^) are divisible by m and m^ respectively, for l^n
^ (pi— 3)/2, where pi is the least prime factor of m, and also gives the resi-
dues of the quotients modulo m. Corresponding theorems therefore hold
for the sum of the products of the integers < m and prime to m, taken t at a.
time.

i"Sitzungsberichte Ak. Wiss. Wien (Math.), 102, 1893, Ila, 1265-94.
"♦Atti R. Accad. Lined, Mem. CI. Fis. Mat., 1, 1894, 344-371.
i«Messenger Math., 28, 1898-9, 39-41.
"»Oversigt Danske Vidensk. Selsk. Forhandlinger, 1915, 509-12; cf. 178-9.

Chap. V] GENERALIZATIONS OF EuLER's 0-FuNCTION. 147

Schemmel's Generalization of Euler's ^-Function.

V. SchemmeP^° considered the $„(m) sets of n consecutive numbers each
<m and relatively prime to m. If m = a'^}f . . ,, where a, h,. . . are distinct
primes, and m, m' are relatively prime, he stated that

$„(m) =a"~^(a — n)6^~-^(5— n) . . ., <^n{mm') =<l>„(m)$n(m'),

Sn"-''V-^'. . .<l>„(5)=w, 6 = a«V. . ., a'^a, /S'^/S, . . .,

the third formula being a generalization of Gauss' (4) . If ^ is a fixed integer
prime to m, $„(w) is the number of sets of n integers <m and prime to m
such that each term of a set exceeds by k the preceding term modulo m.
Consider the productPof the Xth terms of the *J>„(m) sets. If n = 1, P= =t 1
(mod m) by Wilson's theorem. If n> 1,

P"-i=)(-l)^-ir-i(X-l)!(n-X)!j*>) (modm).

For the case A: = X = 1, n = 2, we see that the product of those integers < m
and prime to m, which if increased by unity give integers prime to m, is
= 1 (mod m) .

E. Lucas^^^ gave a generalization of Schemmel's function, without men-
tion of the latter. Let ei,..., e^ be any integers. Let ^(n) denote the
number of those integers h, chosen from 0, 1, . . ., n — 1, such that

h — ei, h — e2,. . ., h — Ck
are prime to n. For k<n, ei = 0, 62= —I,. .., ei,— — {k — 1), we have k con-
secutive integers h, h-j-1,. . ., h+k — l each prime to n, and the number of
such sets is */c(n). Lucas noted that ^(p)'^(g) =^{pq) if p and q are rela-
tively prime. Let n = a°-h^ . . ., where a, h,. . . are distinct primes. Let X
be the number of distinct residues oi ei, . . . , e^ modulo a; fx the number of
their distinct residues modulo h; etc. Then

^(n)=a»-i(a-X)&^-\6-M). . ..
L. Goldschmidt^®^ proved the theorems stated by Schemmel, and himself
stated the further generalization: Select any a — A positive integers <a,
any h—B positive integers <b, etc.; there are exactly

a''-\a-A)¥-\h-B)...
integers <m which are congruent modulo a to one of the a — A numbers
selected and congruent modulo b to one of the h — B numbers selected, etc.
P. Bachmann^^^ proved the theorems due to Schemmel and Lucas.

Jordan's Generalization of Euler's ^-Function.

C. Jordan,^*^*^ in connection with his study of linear congruence groups,
proved that the number of different sets of k (equal or distinct) positive
integers ^n, whose g. c. d. is prime to n, is*

^^ ■/>.w=»'(i-^.)-..(i-^j

"ojour. fur Math., 70, 1869, 191-2. "'Th^orie des nombres, 1891, p. 402.

""Zeitschrift Math. Phys., 39, 1894, 205-212. i^^Niedere Zahlentheorie, 1, 1902, 91-94, 174-5.
^iioTraitg des substitutions, Paris, 1870, 95-97.
*He used the symbol [n, k]. Several of the writers mentioned later used the symbol (f>k(n),
which, however, conflicts with that by Thacker.^^"

148 History of the Theory of Numbers. [Chap, v

if Pi, . . ., Pg are the distinct prime factors of n. In fact, there are n*" sets
of k integers ^n, while {n/piY of these sets have the common divisor pi,

etc., whence

k

+ ....

«"'"•-©•-©■- -(^y

Jordan noted the corollary: if n and n' are relatively prime,

(11) J,{nn')=J,{n)J,{n').

A. Blind^^^ defined the function (10) also for negative values of k, proved
(11), and the following generalization of (4):

(12) 2Ji.(d) =n''' (d ranging over the di\'isors of 7i).

W. E. Story^°^ employed the s>Tnbol r'^in) for Jk{n) and called it one
of the two kinds of kth totients. The second kind is the number </)*(n) of
sets of k integers ^?? and not all di\isible by any factor of n, such that we
do not distinguish between two sets differing only by a permutation of
their numbers. He stated that

<t>\n) =|-,ir*(n)+f,V-nn)+t2V-2(n)+ . • • +<tiT(n)[ ,

where 1, fi*, W,. . . are the coefficients of the successive descending powers
of X in the expansion of (x+l)(x+2). . .{x-\-k — \).

Story-°- defined "the kih. totient of n to the condition k to be the num-
ber of sets of k numbers ^ n which satisfy condition k. The number of sets
of k numbers ^n, all containing some common di\'isor of n satisfying the
condition k, but not all containing any one di\'isor of n satisfying the con-
dition X is (if different permutations of k numbers count as different sets)

'^\H''^-y~b,')y~b,'>)

where 5, 5', . • • are the least divisors of n satisfj-ing condition /c, while
5i, 5/, . . . are the least di\'isors of n satisfying condition x- Here a set of
least divisors is a set of divisors no one of which is a multiple of any other."
E. Ces^ro" (p. 345) stated that, if $;.(a:) is the number of sets of k integers
^x whose g. c. d. is prime to x, then

where J* is to be replaced by J/n), and d ranges over the di\'isors of n.

J. W. L. Glaisher-^^ proved (12) by means of a symbolic expression for
the infinite series 2/t(n)/(a:''). If ^t(n) is Merten's function,

JM -2p,V,(^) +2pi V«/.(^^) - • • =M(n),
where the summations relate to the distinct prime factors p, of n. Using

"* Johns Hopkins University Circulars, 1, 1881, 132.
^^Ihid., p. 151. Cf. Amer. Jour. Math.. 3, 1880, 382-7.
»<»London, Ed. Dublin Phil. Mag., (5), 18, 1884, 531, 537-8.

Chap. V]

Generalizations of Euler's (^-Function.

149

these formulas for n = l, 2,.
each equal to { — lY~'^Jkin):

1^ 2^ 3^ 4^
1111
0 10 1
0 0 10

n, we obtain two determinants of order n,

1

-1

-1

0

-1

1 ...

1

-2"

-3^

0

-5^

6^ ...

0

1'

0

-2'

0

-3* . . .

0

0

1*

0

0

-2' ...

L. Gegenbauer^*^ proved (12). For n = 'pi^ . . .p/'^, set

7r(n) = (-irpi...p„ X(n) = (-l^+••+^

where w{n) denotes the number of distinct prime factors of n. By means
of the series f (s) =Sn~*, he proved that, when d ranges over the divisors of r,

ZF(d)d2' = r^ SF(d)d2' = r'SdV,(d),

^F{d)Jk{d)d'' = 0, S(-l)(^+i)"'(^/V7rM^j =0,

the last holding if r has no square factor and following from the third in
view of (11),

Mr) =2c^m(2) , i:F{d)d'tx{d) =r''fx{r), i:Md)Ud)J,(^^ =0 or J,,{Vr),

according as r is or is not a square,

S ( - 1) ^'+^)"'('"V^(m)/fe(m)/2fe(^)w'* = r''\{r)Jk{r) {mn^ = r) ,

TO, n

^JkM . . .JkinW-^'W-^'"

.nti=r"',

where rii, . . ., n^ range over all sets of solutions of nin2. . .n,+i = n, the case
A; = 1 being due to H. G. Cantor .^^

E. Cesaro^^^ derived (10) from (12), writing ^i_k for Jk.

E. Cesaro^"^ denoted J kin) by xf^'^in) and gave (12).

L. Gegenbauer^^" gave the further generaUzation

X{g,{x)f==i:

i[f]u-),

[^].

J. Hammond^°^ wrote \f/(n, d) for 2/(5), where / is an arbitrary function
and 5 ranges over all multiples ^ n of the fixed divisor d of n. Then

(13) mt)=^^P{n, l)-2)/^(n, pi)+2iA(n, p,P2)-...,

""Sitzungsber. Ak. Wiss. Wien (Math.), 89 II, 1884, 37-46. Cf. p. 841. See Gegenbauer"

of Ch. X.
"'Annali di Mat., (2), 14, 1886-7, 142-6;
"'Messenger Math., 20, 1890-1, 182-190.

150 History of the Theory of Numbers. [Chap, v

where i ranges over the integers ^n which are prime to n, while pi, P2> • • •
denote the distinct prime factors of n. If f{t) = l, then \l/{n, d)=n/d
and (13) becomes

^in)=n-i:^+X-^-...=n(l-^)(l-^)....
Pi P1P2 \ Pi/ V P2/

Next, take f(t) = ao+ait-\-a2f+ .... Using hyperboUc functions,

S/(0 = Jcoth(./2)=l+^-4+...,

provided Z be replaced by nJXn)J_r{n), where

/i(n) =/'(n) -a„ Mn) =f{n) -2a2, . . ., /_i(n) = ff{n)dn.
Hence, since Ji(n) =(j){n),

2/(0 =^/-i(^) +^^-i(n)/i(n) -^V_3(n)/3(n) + . . . .

In particular, for f{t)=t'', we get ^^-(n). In Prouhet's^^ first formula, 5
may be replaced by the g. c. d. A,,, b of a and h. The generalization

J,{ah)=Ma)J,{h)j^^

is proved. From (12) we get by addition*

(14) i\-]j,{j) = l'+2'

y=iLjJ

+ . . . +n*.

Taking n = l, 2,..., n, we obtain equations whose solution gives Jk(n)
expressed as a determinant of order n in which the elements of the last
coluimi are 1, 1+2*, 1+2^+3*, . . ., while for s<n the sth column consists
of s — 1 zeros followed by s units, then s twos, etc. For s>0, the element
in the (s + l)th row and rth column in Glaisher's^"^ first determinant is
1 or 0 according as r/s is integral or fractional.

J. Valyi^°^ used J2{n) ■^({>{n) in his enumeration of the n-fold perspective
polygons of n sides inscribed in a cubic curve.

H. Weber^os proved (10) for k = 2.

L.Carlini209 gave without references (10), (11), (12), with</)(^) for J„(A;).

E. Cesaro^io noted that (12) implies (10). For, if 2/(d) =F(n), we have
by inversion (Ch. XIX), /(n) =Xii{d)F(n/d). The case f=Ji gives

Jijn) _^IJLid)

The latter is a case of G{n) ='2g{d) and hence, with (12) and

W)QQ^2,Wf(^).

♦This work, Mess. Math., 20, 1890-1, p. 161, for k = l, is really due to Dirichlet." Formula
(14) is the case p = 1 of Gegenbauer's, p. 217.
"^Math. Nat. Berichte aus Ungarn, 9, 1890, 148; 10, 1891, 171.
"'EUiptische Functioncn, 1891, 225; ed. 2, 1908 (Algebra III), 215.
"»Periodico di Mat., 6, 1891, 119-122.
"o/fcid., 7, 1892, 1-6.

Chap. V] GENERALIZATIONS OF EuLER's </)-FuNCTION. 151

Ji+M=i:d'JMJi(^,

which is next to the last formula of Gegenbauer's.^"^ Similarly,

which is the case i = 1 of Gegenbauer's'^^ fifth formula in Ch. X, (Tk{n) being
the sum of the A;th powers of the divisors of n.

E. Weyr^^^ interpreted J2in) in connection with involutions on loci of
genus 1. From the same standpoint, L. Gegenbauer^^^ proved (12) for
k = 2 and noted that the value (10) of J-zin) then follows by the usual method
of number-theoretic derivatives.

L. Gegenbauer^^^" wrote cf)kim, n) for the number of sets of k positive
integers ^ m whose g. c. d. is prime to n = pi°' . . . p/'' and proved a formula
including

[mf=Um, n)+i S {\„ . . . XT 4>k i -^ • , -^^ )

where (Xi, . . . , X,,) is the determinant derived from that with unity through-
out the main diagonal and zeros elsewhere by replacing the 7th row by
the X^th row for 7 = 1,. . ., c. The case m = n, k — l, is due to Pepin.^^
There is an analogous formula involving the sum of the /cth powers of the
positive integers ^m and prime to n.

E. Jablonski^^ used Jk{n) in connection with permutations.

G. Arnoux^^^ proved (10) in connection with modular space.

*J. J. Tschistiakow^^"* (or Cistiakov) treated the function /^(n).

R. D. von Sterneck^^^ proved that

J,{n) =SJ,(Xi)J,_,(X2) =S0(X,) . . 4{\),

the X's ranging over all sets of integers S. n whose 1. c. m. is n. To generalize
this, let Jk{n; mi, ... , rrik) be the number of sets of integers z'l, . . . , ik, whose
g. c. d. is prime to n, while ij^n/mj for j = 1, . . . , k. Then

Jk{n; Wi, . . ., m^)=SJ,(Xi; m\,. . ., 'm'r)Jk-r0^2] ^'r+i,- • •, rn'k)
=2:Ji(Xi; mi). . . J'i(X^; m^),

the X's ranging over all sets of integers ^n whose 1. c. m. is n, while m'l, . . . ,
m'k form any fixed permutation of mi, . . . , m^t, and J"i(n; m), designated
<f)^"'\n) by the author, is the number of integers ^n/m which are prime
to n. Also,

"iSitzungsberichte Ak. Wiss. Wien (Math.), 101, Ila, 1892, 1729-1741.
2i2Monatshefte Math. Phys., 4, 1893, 330.
2i2aDenkschr. Ak. Wiss. Wien (Math.), 60, 1893, 25-47.
2i'Arithm6tique graphique; espaces arith. hypermagiques, 1894, 93.
2"Math. Soc. Moscow, 17, 1894, 530-7 (in Russian).
"'Monatshefte Math. Phys., 5, 1894, 255-266.

152 History of the Theory of Numbers. [Chap, v

SJ.(d;m„...,m.) = [ii]W...[iL],

where d ranges over the divisors of n, the case A; = 1 being due to Laguerre.'*
In the latter case, take n = 1, . . . , n and add. Thus

k=i LfcJ -^^LmJ Ini m \ m/ j

the last equality, in which (n, h) is the g. c. d. of n, h, following from expres-
sions for (n, h) given by Hacks^^ of Ch. XL In the present paper the above
double equation was proved geometrically. For m = l, we get Dirichlet's^^
formula. The g. c. d. of three numbers is expressed in terms of them and [x].
The initial formulas were proved geometrically, but were recognized to
be special cases of a more general theorem. Let

2Md)=FM (1 = 1, ...,k),

where d ranges over all divisors of n. Then the function

^(n) =S/i(Xi) . . .A(X,) (1. c. m. of Xj, . . . , X* is n)

has the property

S^(d)=Fi(n)...n(n).

Hence in the terminology of Bougaief (Ch. XIX) the number-theoretic
derivative ^{n) of Fi{n) . . .Fk{n) equals the sum of the products of the
derivatives /» of the factors Fi, the arguments ranging over all sets of k
numbers having n as their g. c. d.

L. Gegenbauer^^^" proved easily that, if [n, . . , t] is the g. c. d. of n, . . . , f

2 F{[n,x^,...,x,]) = 'E F{d)jJ fj,

where d ranges over all divisors of n, and F is any function.

K. Zsigmondy^^^ considered any abelian (commutative) group G with
the independent generators ^i,. . ., Qs of periods ni, . . ., n^, respectively.
Any element g'l''' . . . gj"' of G is of period 5 if and only if 5 is the least positive
value of X for which xhi,. . ., xhs are multiples of rii, . . ., n^, respectively.
The number of elements of period 5 of G is thus the number of sets of posi-
tive integers hi,. . ., hg {hi^rii,. . ., /ij^nj such that 5 is the least value of
X for which xhi,. . . , xhs are divisible by ni, . . . , n^, respectively. The num-
ber of sets is shown to be

rPid;ni,...,n,)=lldjIl{l-l/q.'*),

where 5_, is the g. c. d. of 5 and Uj] q\,...,qr are the distinct prime factors
of 5; while U is the number of those integers nx, . . ., n^ which contain q^
at least as often as 5 contains it. If 5 and 5' are relatively prime,

ypib] ni,. . ., n,)\pi8'; rii,. . ., n,)=i/'(55'; nj. . ., nj.

"li^Sitzungsber. Akad. Wiss. Wien (Math.), 103, Ila, 1894, 115.

"'Monatshefte Math. Phys., 7, 1896, 227-233. For his 0 we write \p, as did Carmichael."

I

Chap. V] GENERALIZATIONS OF EuLER's 0-FuNCTION. 153

If d ranges over all divisors of the product ni . . . n^,

Si//(5;ni, . . ., n,)=nin2. . .n,.

d

In case 5 divides each ni{i = \, . . ., s), 4/ becomes Jordan's Js(5).

As a generalization (pp. 237-9) consider sets of positive integers ai, . . . , a„
where aj = l, 2, . . . , 7_, for j = 1, 2, . . . , s. Counting the sets not of the form

n^ai, nf a2, . . . , n^f a, (i = l,. ..,r),

we get the number

n 7,-2 n \-%\ +s n f. J' ,,,~\ -

where (ni, n2, . . .) is the 1. c. m. of rii, n2, . . .. In particular, take

n^P= . . . =n^f = ni (i = l,...,r),

where ni, . . . , n^. are relatively prime in pairs, and let iV be a positive mul-
tiple of ni, . . . , n^ such that

Then the above expression equals

J/(iV; mi,. . ., m,) = n T-l-S II [—1 + 2 H f-^^l - . • .,
y=iLmyJ i j=\unjniA i,i' j=\unjnini>j

which determines the number of sets

tti,. . ., a, (ay = l, 2,. . ., — ;i=l,. . ., s)

l_A/tyJ

whose g. c. d. is divisible by no one of ni, ^2, . . . , n^. By inversion,

S//g;^„...,m.) = n[|],

where d ranges over the divisors of N which are products of powers of
rii, . . . , Ur. When ni,...,ns are the distinct prime factors of N,J/{N; rrii, . . , ,
m,) becomes the function Js{N; mi, . . ., Wj) of von Sterneck.^^^ As in the
case of the latter function, we have

J/{N; Wi,. . ., m,)=SJi'(Xi; mi). . .//(X,; mj,
the X's ranging over all sets whose 1. c. m. is N.

L. Carhni^^^ proved that if a ranges over the integers for which [2n/a]
= 2/c+l, then

XJM = sg^ - 2s^'J, s^^ ^1'+... +m*.

For k = l, this becomes 2(^(a) =n^ [E. Cesaro, p. 144 of this History].

D. N. Lehmer^^^ called Jmin) the m-fold totient of n or multiple totient
of n of multiplicity m. He proved that, if A: = pi"'. . .pr°^

Jm{k'')=k^'''-''Jm{k), Jm(ky)=JM n \pr^-pr"^-'Xy, Pi) \ ,

1=1
where \(y, pj =0 or 1 according as Pi is or is not a divisor of y. In the

'"Periodico di Mat., 12, 1897, 137-9.
"»Amer. Jour. Math., 22, 1900, 293-335.

154 History of the Theory of Numbers. [Chap, v

second formula the product equals the similar function of y' if y and y' are
congruent modulo pip^ ■ ■ Pr- Consider the function

U/k]

1=1
where m, n, k are positive integers and x is a positive number. Then if
S{x, k) denotes l*+2''-f . . . H-[x]*, it is proved that

which for m = n = 1 becomes Sylvester's^^ formula. By inversion,
where ai(i) is Merten's function. For k as above and k' = k/pr''^,

^,

.(X, n, A;)=p,-(v-i)|(p^-i)ci,^(^^, n, A:')+$^(^, n, p,k') |

= p,'"(«r-i)(p^_l)Sp^-^-i),^^/'^, n, A;'),

where I is the least value of j for which [x/p^"'""^-'] = 0. Hence $^(x, n, k)
can be expressed in terms of functions $,„(?/, n, 1). True relations are
derived from the last four equations by replacing n by 1 — n and ^m{Xy 1 — n,
A:) by

\xlk\

n^{x,n,k)=i:j^{ik)'(ik)-'''".
1=1

Proof is given of the asymptotic formula

„»n7i+l p

^'"(^' ^' ^)=:;;;:;rxT 7r^+^' hl^^x-- log x,

wn + l D^+i

where A is finite and independent of x, ??2, n, while

« 1 *■ Pi — I

Dm+i = 2 — q:Y> P^. fc = n a^_w „+i 7TJ P„,. 1 = 1.

j = U i=lPi \Pi —i-j

For m = n = fc = l, this result becomes that of Mertens^* (and Dirichlet'^).

The asymptotic expressions found for ^^i^, n, k) are different for the cases

n = l, n = 2, n>2.

A set of m integers (not necessarily positive) having no common divisor
> 1 is said to define a totient point. Let one coordinate, as x^, have a
fixed integral value 5^0, while Xi,. . ., x^-i take integral values such that
[xi/x^],. . ., [X;„_i/X;„] have prescribed values; we obtain a compartment in
space of m dimensions which contains /m-i(^m) totient points. For
example, if m = 3, X3 = 6, and the two prescribed values are zero, there are
24 totient points (xi, X2, 6) for which 0^Xi<6, 0^X2<6, while Xi and X2
have no common divisor dividing 6. For Xi = l or 5, Xo has 6 values; for
Xi = 2 or 4, X2=l, 3 or 5; for Xi = 3, X2 = l, 2, 5; for Xi = 0, X2 = 0, 1, 5.

Given a closed curve r=f{d), decomposable into a finite number of seg-
ments for each of which f{d) is a single- valued, continuous function. Let

I

Chap. V] FarEY SeRIES. 155

K be the area of the region bounded by this curve, and N the number of
points {x, y) within it or on its boundary such that a; is a multiple of k and
is prime to y. Then ^ ^

lim— = -2Pi.fc,

k=aa A TT

where K increases by uniform stretching of the figure from the origin.

In particular, consider the number A^ of irreducible fractions x/y^\
whose denominators are ^n. Since x^y, the area K of the triangular re-
gion is n^/2. Hence N = {n^/2) (6/7r^) , approximately (Sylvester^^) . Again,
the number of irreducible fractions whose numerators he between I and
l-\-m, and denominators between V and I'+m', is Qmm'/ir^, approximately.

There is a similar theorem in which the points are such that y is divisible
by k', while three new constants obey conditions of relative primality to
each other or to x, y, k, k'.

Extensions are stated for m-dimensional space.

E. Cahen^^^ called /^(n) the indicateur of /cth order of n.

G. A. Miller^^° evaluated Jk{in) by noting that it is the number of
operators of period m in the abeUan group with k independent generators
of period m.

G. A. Miller^^^ proved (10) and (11) by using the same abelian group.

E. Busche^^^ indicated a proof of (10) and (12) by an extension to space
oi k+1 dimensions of Kronecker's^^^ plane, in which every point whose
rectangular coordinates x, y are integers is associated with the g. c. d. of x, y.

A. P. Minin^^^ proved (14) and some results due to Gegenbauer.^"^

R. D. CarmichaeP^^ gave a simple proof of Zsigmondy's^^® formula for ^.

G. Metrod^^^ stated that the number of incongruent sets of solutions
of xy' — x'y = a (mod m) is 'EdmJ2{m/d), where d ranges over the common
divisors of m and a. When a takes its m values, the total number of sets
of solutions is vJ'Ay^ rt'A

It is asked if like relations hold for Jk, k>2.

Cordone^^ and Sanderson^^^ (of Ch. VIII) used Jordan's function in
giving a generalization of Fermat's theorem to a double modulus.

Farey Series.

Flitcon^^ gave the number of irreducible fractions <1 with each
denominator <100, stating in effect the value of Euler's (/)(n) when
n is a product of four or fewer primes.

"9Th6orie des nombres, 1900, p. 36; I, 1914, 396-400.
«»Amer. Math. Monthly, 11, 1904, 129-130.
2"Amer. Jour. Math., 27, 1905, 321-2.
222Math. Annalen, 60, 1905, 292.
^^'Vorlesungen iiber Zahlentheorie, 1901, I, p. 242.
224Matem. Sbomik (Moscow Math. Soc), 27, 1910, 340-5.
"^''Quart. Jour. Math., 44, 1913, 94-104.

«2«L'interm6diaire des math., 20, 1913, 148. Proof, Sphinx-Oedipe, 9, 1914, 4.
^'Ladies' Diary, 1751. Reply to Question 281, 1747-8. T. Leybourn's Math. Quest, pro-
posed in Ladies' Diary, 1, 1817, 397-400.

156 History of the Theory of Numbers. [Chap, v

C. Haros-"*^ proved the results rediscovered by Farey-^° and Caiichy.^^-
J. Farey-^" stated that if all the proper vulgar fractions in their lowest
terms, having both numerator and denominator not exceeding a given
number n, be arranged in order of magnitude, each fraction equals a frac-
tion whose numerator and denominator equal respectively the sum of the
numerators and sum of the denominators of the two fractions adjacent to it
in the series. Thus, for n = 5, the series is

1112 13 2 3 4
Z' T' -JT' T' IT' T' 7' T' T'

and

1_1 + 1 2_1 + 1.

4 5+3' 5 3+2*

Henry Goodwyn mentioned this property on page 5 of the introduction
to his "tabular series of decmial quotients" of 1818, published in 1816 for
private circulation (see Goodwyn,^^' ^- Ch. VI), and is apparently to be
credited with the theorem. It was ascribed to Goodwyn by C. W. Merri-
field.2"

A. L. Cauchy^^^ proved that, if a/b, a'/b', a"/b" are any three consecu-
tive fractions of a Farey series, b and b' are relatively prime and a'b—ab' = 1
(so that a'/b'-a/b = l/bb'). Similarly, a"b'-a'b" = l, so that a+a": b+b"
= a': b', as stated by Farey.

StouveneP^^ proved that, in a Farey series of order n, if two fractions
a/b and c/b are complementary (i. e., have the sum unity), the same is true
of the fraction preceding a/b and that following c/b. The two fractions
adjacent to 1/2 are complementary and their common denominator is the
greatest odd integer ^n. Hence 1/2 is the middle term of the series and
two fractions equidistant from 1/2 are complementary. To find the third
of three consecutive fractions a/b, a'/b', x/y, we have a+x = a'z, b+y = b'z
(Farey), and we easily see that z is the greatest integer ^ {n-\-b)/b',

M. A. Stern-^^ studied the sets m, n, and m, m-\-n, n, and m, 2m-\-n,
m-\-n, m-\-2n, n, etc., obtained by interpolating the sum of consecutive
terms. G. Eisenstein^^" briefly considered such sets.

*A. Brocot^^'' considered the sets obtained by mediation [Farey] from
U/1, 1/0: oil. 01121.

T' T' ITJ T' Y' 1' T' TJ">- • ••

Herzer^^^ and Hrabak^^^ gave tables with the limits 57 and 50.

G. H. Halphen^^^ considered a series of irreducible fractions, arranged
in order of magnitude, chosen according to a law such that if any fraction /
is excluded then also every fraction is excluded if its two terms are at least

2<9Jour. de I'dcole polyt., cah. 11, t. 4, 1802, 364-8.

"oPhilos. Mag. and Journal, London, 47, 1816, 385-6; [48, 1816, 204]; Bull. Sc. Soc. Philomatique

de Paris, (3), 3, 1816, 112.
"'Math. Quest. Educat. Times, 9, 1868, 92-5.
"*Bufl. Sc. Soc. Philomatique de Paris, (3), 3, 1816, 133-5. Reproduced in Exercices de Math.,

1, 1826, 114-6; Oeuvres, (2), 6, 1887, 146-8.
"»Jour. de mathdmatiques, 5, 1840, 265-275.

»«Jour. fur Math., 55, 1858, 193-220. "laBericht Ak. Wiss. Berlin, 1850, 41^2.

"'Calcul des rouages par approximation, Paris, 1862. Lucas.'"

2^«Tabellen, Basle, 1864. ""Tabellen-Werk, Leipzig, 1876.

"'Bull. Soc. Math. France, 5, 1876-7, 170-5.

Chap. V] FaREY SeRIES. 157

equal to the corresponding terms of /. Such a series has the properties
noted by Farey and Cauchy for Farey series.

E. Lucas^^^ considered series 1, 1 and 1, 2, 1, etc., formed as by Stern.
For the nth series it is stated that the number of terms is 2"~-^ + l, their
sum is 3""^ + l, the greatest two terms (of rank 2""^+l=±=2"~^) are

(i+V5r+^-(i-\/5r+^

2"+V5

Changing n to p, we obtain the value of certain other terms.

J. W. L. Glaisher^^° gave some of the above facts on the history of Farey
series. Glaisher^" treated the history more fully and proved (p. 328) that
the properties noted by Farey and Cauchy hold also for the series of irre-
ducible fractions of numerators ^ m and denominators ^ n.

Edward Sang^^" proved that any fraction between A/ a and C/y is'of
the form {'pA-[-qC)/{'pa-{-qy), where p and q are integers, and is irreducible
if p, q are relatively prime.

A. Minine^®^ considered the number S{a, N) of irreducible fractions a/h
such that h-\-aa^N. Let 0(6)p denote the number of integers ^p which
are prime to h. Then, for a > 0,

>S(a,iV)= S0(6)p, P=L a J'

since for each denominator h there are (/)(6)p integers prime to h for which
h+aa-^N and hence that number of fractions.

A. F. Pullich^^^ proved Farey's theorem by induction, using continued
fractions.

G. Airy^^^ gave the 3043 irreducible fractions with numerator and denom-
inator ^ 100.

J. J. Sylvester^^^ showed how to deduce the number of fractions in a
Farey series by means of a functional equation.

Sylvester,^^' ^^ Cesaro,^^ Vahlen,^^ Axer,^^^ and Lehmer^^^ investigated the
number of fractions in a Farey series.

Sylvester^^^" discussed the fractions x/y for which x<n^ y<n, x-\-y^n.

M. d'Ocagne^^'^ prolonged Farey's series by adding 1/1 in the pth place,
where p=<^(l)+ . . . +(j>{n). From the first p terms we obtain the next p
by adding unity, then the next p by adding unity, etc. Consider a series
S{a, N) of irreducible fractions Ui/hi in order of magnitude such that
bi+atti^N, where a is any fixed integer called the characteristic. All
the series S(_a, N) with a given base N may be derived from Farey's series

««Bull. Soc. Math. France, 6, 1877-8, 118-9. ^oProc. Cambr. Phil. Soc, 3, 1878, 194.

MiLondon Ed. Dub. Phil. Mag., (5), 7, 1879, 321-336.
'"Trans. Roy. Soc. Edinburgh, 28, 1879, 287.

"'Jour, de math. el6m. et spec, 1880, 278. Math. Soc. Moscow, 1880.

'"Mathesis, 1, 1881, 161-3. '"Trans. Inst. Civil Engineers; cf. Phil. Mag., 1881, 175.

'"Johns Hopkins Univ. Circulars, 2, 1883, 44-5, 143; Coll. Math. Papers, 3, 672-6, 687-8.
266aAmer. Jour. Math., 5, 1882, 303-7, 327-330; Coll. Math. Papers, IV, 55-9, 78-81.
'"Annales Soc. Sc. Bruxelles, 10, 1885-6, II, 90. Extract in Bull. Soc. Math. France, 14, 1885-6,
93-7.

158 History of the Theory of Numbers. [Chap, v

5(0, N) by use of

a.(a, N) =a,(0, N), &.(a, iV) =6,(0, N) -aa,(0, N).

Thus a,6._i — a,_i6i = l, so that the area of OA.A,_i is 1/2 if the point
Ai has the coordinates o,, 6,. All points representing terms of the same
rank in all the series of the same base he at equally spaced intervals on a
parallel to the x-axis, and the distance between adjacent points is the num-
ber of units between this parallel and the a:-axis.

A. Hurwitz-^^ apphed Farey series to the approximation of numbers
by rational fractions and to the reduction of binary quadratic forms.

J. Hermes-^^ designated as numbers of Farey the numbers ri = l, 72 = 2,
X3 = 7^ = 3, To = 4, tq = t7 = 5, t8 = 4, . . . with the recursion formula

T„ = r„_2^+r2^+i-n+i, 2''<n^2'+\

and connected with the representation of numbers to base 2. The ratios
of the r's give the Farey fractions.

K. Th. Vahlen-^^'' noted that the formation of the convergents to a
fraction w by Farey's series coincides with the development of w into a con-
tinued fraction whose numerators are ±1, and made an application to the
composition of linear fractional substitutions.

H. Made-'° apphed Hurwitz's method to numbers a+hi.

E. Busche"^ apphed geometrically the series of irreducible fractions of
denominators ^a and numerators ^b, and noted that the properties of
Farey series {a = h) hold [Glaisher-®^].

W. Sierpinski^^^ used consecutive fractions of Farey series of order m
to show that, if x is irrational.

===« U=i^ ^ 2 2j

Expositions of the theory of Farey series were given by E. Lucas,'"
E. Cahen,-'^ Bachmann.^'^

An anonymous writer,^'^ starting with the irreducible fractions <1,
arranged in order of magnitude, with the denominators ^ 10, inserted the
fractions with denominator 11 by listing the pairs of fractions 0/1, 1/10;
1/6, 1/5; 1/4, 2/7;. . ., the sum of whose denominators is 11, and noting
that between the two of each pair lies a fraction with denominator 11 and
numerator equal the sum of their numerators.

*«8Math. Annalen, 44, 1894, 417-436; 39, 1891, 279; 45, 1894, 85; Math. Papers of the Chicago
Congress, 1896, 125. Cf. F. Klein, Ausgewahlte Kapitel der Zahlentheorie, I, 1896,
19^210. Cf. G. Humbert, Jour, de Math., (7), 2, 1916, 116-7.

*«9Math. Annalen, 45, 1894, 371. Cf. L. von Schrutka, 71, 1912, 574, 583.

^s'ajour. fiir Math., 115, 1895, 221-233.

^'^Ueber Fareysche Doppelreihen, Diss. Giessen, Darmstadt, 1903.

"'Math. Annalen, 60, 1905, 288.

*"BuU. Inter. Acad. Sc. Cracovie, 1909, II, 725-7.

»"Th6orie des nombres, 1891, 467-475, 508-9.

*'^fil4ments de la theorie des nombres, 1900, 331-5.

"'Niedere Zahlentheorie, 1, 1902, 121-150; 2, 1910, 55-96.

i^'OZeitschrift Math. Naturw. Unterricht, 45, 1914, 559-562.

CHAPTER VI.

PERIODIC DECIMAL FRACTIONS; PERIODIC FRACTIONS: FACTORS

OF I0"±1.

Ibn-el-Banna^ (Albanna) in the thirteenth century factored 10" — 1 for
small values of n. The Arab Sibt el-Maridini^" in the fifteenth century
noted that in the sexagesimal division of 47° 50' by 1° 25' the quotient
has a period of eight terms.

G. W. Leibniz^ in 1677 noted that \/n gives rise to a purely periodic
fraction to any base h, later adding the correction that n and h must be
relatively prime. The length of the period of the decimal fraction for 1/n,
where n is prime to 10, is a divisor of n — 1 [erroneous for n = 21 ; cf . Wallis^] .

John Wallis^ noted that, if N has a prime factor other than 2 and 5, the
reduced fraction M/N equals an unending decimal fraction with a repetend
of at most A^ — 1 digits. If N is not divisible by 2 or 5, the period has two
digits if N divides 99, but not 9; three digits if A^ divides 999, but not 99.
The period of 1/21 has six digits and 6 is not a divisor of 21 — 1. The
length of the period for the reciprocal of a product equals the 1. c. m. of
the lengths of the periods of the reciprocals of the factors [cf. Bernoulli^].
Similar results hold for base 60 in place of 10.

J. H. Lambert^ noted that all periodic decimal fractions arise from
rational fractions; if the period p has n digits and is preceded by a decimal
with m digits, we have

lO'" ' lO'^lO" lO'^lO^" lO'^ClO^-l)

John Robertson^ noted that a pure periodic decimal with a period P of
k digits equals P/9 ... 9, where there are k digits 9.

J. H. Lambert^ concluded from Fermat's theorem that, if a is a prime
other than 2 and 5, the number of terms in the period of \/a is a divisor
of a — 1. If S' is odd and \/g has a period oi g — 1 terms, then ^ is a prime.
If \/g has a period of m terms, but ^ — 1 is not divisible by m, g is composite.
Let 1/a have a period of 2m terms; if a is prime, A; = lO'^+l is divisible by
a; if a is composite, k and a have a common factor; if k is divisible by a
and if m is prime, each factor other than 2^5^ of a is of period 2m.

Let a be a composite number not divisible by 2, 3 or 5. If 1/a has a
period of m terms, where w is a prime, each factor of a produces a period

'Cf. E. Lucas, Arithm^tique amusante, 1895, 63-9; Brocard.'o^

i«Carra de Vaux, Bibliotheca Matb., (2), 13, 1899, 33-4.

^Manuscript in Bibliothek Hannover, vol. Ill, 24; XII, 2, Blatt 4; also. III, 25, Blatt 1, seq.,

10, Jan., 1687. Cf. D. Mahnke, BibUotheca Math., (3), 13, 1912-3, 45-48.
^Treatise of Algebra both historical & practical, London, 1685, ch. 89, 326-8 (in manuscript,

1676).
*Acta Helvetica, 3, 1758, 128-132.
»Phil. Trans., London, 58, 1768, 207-213.
"Nova Acta Eruditorum, Lipsiae, 1769, 107-128.

159

160 History of the Theory of Numbers. [Chap, vi

of m terms. If \/a has a period of mn terms, where m and n are primes,
while no factor has such a period, one factor of a divides 10'" — 1 and another
di\'ides 10" — 1. If \/a has a period of mnp terms, where vi, n, p are primes,
but no factor has such a period, any factor of a divides 10"*- 1,. . ., or
10"" — !. These theorems aid in factoring a.

L. Euler^ gave numerical examples of the conversion of ordinary frac-
tions into decimal fractions and the converse problem.

Euler^'' noted that if 2p+l is a prime 40?2±1, ±3, ±9, ±13, it divides
lO^-ljif 2p + l isaprime40;?±7, ±11, ±17, ±19, it divides 10^+1.

Jean BernouUi^ gave a r^sum6 of the work by Wallis,^ Robertson,*
Lambert^ and Euler,^ and gave a table showing the full period for 1/D for
each odd prime D<200, and a like table when Z) is a product of two equal
or distinct primes < 25. When the two primes are distinct, the table con-
firms Wallis' assertion that the length of the period for 1/D is the 1. c. m.
of the lengths of the periods for the reciprocals of the factors. But for
l/D^, where D is a prime > 3, the length of the period equals D times that
for 1/D. If the period for 1/D, where D is a prime, has D — 1 digits, the
period for ?n/D has the same digits permuted cyclically to begin with m.
He gave (p. 310) a device communicated to him by Lambert: to find the
period for 1/D, where Z) = 181, we find the remainder 7 after obtaining the
part p composed of the first 15 digits of the period; multiply l/D = p-\-7/D
by 7 ; thus the next 15 digits of the period are given by 7p ; since 7^ = /)+ 162,
the third set of 15 digits is found by adding unity to 7~p, etc.; since 7
belongs to the exponent 12 modulo D, the period for 1/D contains 15-12
digits.

Jean Bernoulli^ made use of various theorems due to Euler which give
the possible linear forms of the divisors of 10*±1, and obtained factors of
(10*-l)/9 when A-^30, except for k = ll, 17, 19, 23, 29, with doubt as to
the primality of the largest factor when A' = 13, 15 or ^19. He stated
(p. 325) erroneously^^ that (10^^ + l)/ll-23 has no factor <3000. Also,

10''+1 = 7-1M3-211-9091-520S1.

He gave part of the periods for the reciprocals of various primes ^601.

L. Euler^^ wTote to Bernoulli concerning the latter's^ paper and stated
criteria for the divisibility of 10^±1 by a prime 2p + l=4n±l. If both
2 and 5 or neither occur among the divisors of n, n=F2, n=F6, then 10'' — 1
is divisible by 2p-\-l. But if only one of 2 and 5 occurs, then 10^+1 is
divisible by 2p+l [cf. Genocchi^^].

Henry Clarke^^ discussed the conversion of ordinary fractions into
decimals without dealing with theoretical principles.

'Algebra, I, Ch. 12, 1770; French trans!., 1774.
'"Opusc. anal., 1, 1773, 242; Comm. Arith. Coll., 2, p. 10, p. 25.
'Nouv. m6m. acad. roy. Berlin, ann^e 1771 (1773), 273-317.
*Ibid., 318-337.

"P. Seelhoff, Zeitschrift Math. Phys., 31, 1886, 63. Reprinted, Sphinx-Oedipc, 5, 1910, 77-8.
"Nouv. m(Sm. acad. roy. Berlin, annde 1772 (1774), Histoire, pp. 35-36; Comm. Arith., 1, 584.
^^he rationale of circulating numbers, London, 1777, 1794.

\

Chap. VI] PERIODIC DECIMAL FRACTIONS. 161

Anton FelkeP^ showed how to convert directly a periodic fraction
written to one base into one to another base. He gave all primes < 1000
which can divide a period with a prime number of digits <30, as 29m +1
= 59,233,....

Oberreit^* extended Bernoulli's^ table of factors of 10*=*=!.

C. F. Gauss^^ gave a table showing the period of the decimal fraction for
Vp", p"<467, V a prime, and the period for 1/p", 467^ p"^ 997.

W. F. Wucherer^® gave five places of the decimal fraction for n/d,
d<1000, n<dford<50, n^ 10 for (^^ 50.

Schroter published at Helmstadt in 1799 a table for converting ordinary
fractions into decimal fractions.

C. F. Gauss^'^ proved that, if a is not divisible by the prime p (^7^2, 5),
the length of the period for a/p" is the exponent e to which 10 belongs
modulo p^. If we set 0(p") =ef and choose a primitive root r of p^ such
that the index of 10 is /, we can easily deduce from the periods for k/p^,
where k = \, r, . . ., r^~\ the period for m/p", where m is any integer not
divisible by p. For, if i be the index of m to the base r, and if i = af-\-^,
where 0^/3</, we obtain the period for m/p" from that for rVp" by carrying
the first a digits to the end. He computed^^ the necessary periods for each
p"<1000, but published here the table only to 100. By using partial
fractions, we may employ the table to obtain the period for a/b, where b
is a product of powers of primes within the limits of the table.

H. Goodwyn^^ noted that, if a<17, the period for a/17 is derived from
the period for 1/17 by a cyclic permutation of the digits. Thus we may
print in a double line the periods for 1/17, . . . , 16/17 by showing the period
for 1/17 and, above each digit d of the latter, showing the value of a such
that the period for a/ 17 begins with the digit d, while the rest of the
period is to be read cyclically from that for 1/17.

Goodwyn^^ noted that when 1/p is converted into a decimal fraction,
p being prime, the sum of corresponding quotients in the two half periods
is 9, and that for remainders is p, if p^7.

J. C. Burckhardt^" gave the length of the period for 1/p for each prime
p^2543 and for 22 higher primes. It follows that 10 is a primitive root
of 148 of the 365 primes p, 5<p<2500.

"Abhand. Bohmiachen Gesell. Wias., Prag, 1, 1785, 135-174.

"J. H. Lambert's Deutscher Gelehrter Briefwechsel, pub. by J. Bernoulli, Leipzig, vol. 5,
1787, 480-1. The part (464-479) relating to periodic decimals is mainly from Ber-
noulli's' paper.

"Posthumous manuscript, dated Oct., 1795; Werke, 2, 1863, 412-434.

^'Beytrage zum allgemeinem Gebrauch der Decimal Brliche. . . ., Carlsruhe, 1796.

"Disq. Arith., 1801, Arts. 312-8. A part was reproduced by Wertheim, Elemente der Zahlen-
theorie, 1887, 153-6.

I'Jour. Nat. Phil. Chem. Arts (ed., Nicholson), London, 4, 1801, 402-3.

"76id., new series, 1, 1802, 314-6. Cf. R. Law, Ladies' Diary, 1824, 44-45, Quest. 1418.

'"Tables des diviseurs pour tous les nombres du premier milMon, Paris, 1817, p. 114. For errata
see Shanks," Kessler," Cimningham,^^! and G^rardin."^

162 History of the Theory of Numbers. [Chap, vi

H. Goodw-jTi-^ gave for each integer d^ 100 a table of the periods for
n/d, for the various integers n<d and prime to d. Also, a table giving
the first eight digits of the decimal equivalent to everj^ irreducible vulgar
fraction < 1/2, whose numerator and denominator are both ^ 100, arranged
in order of magnitude, up to 1/2.

GoodwATi"' -^ was without doubt the author of two tables, which refer
to the preceding ''short specimen" by the same author. The first gives
the first eight digits of the decimal equivalent to every irreducible \'ulgar
fraction, whose numerator and denominator are both ^ 1000, from 1/1000
to 99/991 arranged in order of magnitude. In the second volume, the
"table of circles" occupies 107 pages and contains all the periods (circles)
of ever}' denominator prime to 10 up to 1024; there is added a two-page
table showing the quotient of each number ^ 1024 by its largest factor 2°5''.

For example, the entry in the "tabular series" under -^^ is .08689024.
The entry in the two-page table under 656 is 41. Of the various entries
under 41 in the "table of circles," the one containing the digits 9024 gives
the complete period 90243. Hence /^V = -086890243.

Glaisher"^ gave a detailed account of Goodwyn's tables and checks on
them. They are described in the British Assoc. Report, 1873, pp. 31-34,
along -wdth tables showing seven figures of the reciprocals of numbers
< 100000.

F. T. Poselger'^ considered the quotients 0, a, h,. . . and the remainders
1, a, j8, . . . obtained by di\'iding 1, ^, A~, ... by the prime p; thus

A a A' .,.B

—=a-i — , — = aA+b-\ — ,....

P P P P

Adding, we see that the sum lH-a-}-/3-|- ... of the remainders of the period
is a multiple TTzp of p; also, w(A — 1) =a+6-f- . . .. Set

M = k+...+hA'-'--\-aA*-\
where A belongs to the exponent t modulo p. Then

— = -+MS, S = l+A'+ . . . +A^"-'\

P P

"The first centenarj' of a series of concise and useful tables of all the complete decimal quotients
which can arise from dividing a unit, or any whole number less than each divisor, by all
integers from 1 to 1024. To which is now added a tabular series of complete decimal
quotients for all the proper vulgar fractions of which, when in their lowest terms, neither
the numerator nor the denominator is greater than 100; with the equivalent vulgar
fractions prefixed. By Henry Goodwyn, London, 1818, pp. xiv + lS; vii+30. The first
part was printed in 1816 for private circulation and cited by J. Farey in Philos. Mag. and
Journal, London, 47, 1816, 385.

"A tabular series of decimal quotients for all the proper vulgar fractions of which, when in their
lowest terms, neither the numerator nor the denominator is greater than 1000, London,
1823, pp. v + 153.

"A table of the circles arising from the division of a unit, or any other whole number, by all the
integers from 1 to 1024; being all the pure decimal quotients that can arise from this
source, London, 1823, pp. v + 118.

"Abhand. Ak. Wiss. BerUn (Math.), 1827, 21-36.

Chap. VI] PERIODIC DECIMAL FRACTIONS. 163

If M is divisible by p, we may take n = 1 and conclude that A^p^ differs
from 1/p^ by an integer. If M is not divisible by p, S must be, so that n
is divisible by p and the length of the period is pt. In general, for the denom-
inator p^, we have n = l if M is divisible by p^~^, but in the contrary case
n is a multiple of p'"'^. If the period for a prime p has an even number of
digits, the sum of corresponding quotients in the two half periods is p.

An anonymous writer^^ noted that, if we add the digits of the period of
a circulating decimal, then add the digits of the new sum, etc., we finally
get 9. From a number subtract that obtained by reversing its digits; add
the digits of the difference; repeat for the sum, etc.; we get 9.

Bredow^^ gave the periods for a/p, where p is a prime or power of a
prime between 100 and 200. He gave certain factors of 10" — 1 for w = 6-10,
12-16, 18, 21, 22, 28, 33, 35, 41, 44, 46, 58, 60, 96.

E. Midy" noted that, if a"", a"', . . . are the least powers of a which,
diminished by unity, give remainders divisible by q^, qi''', . . . , respectively
{q, qi,... being distinct primes), and if the quotients are not divisible by
q, qi,. . ., respectively, and if t is the 1. c. m. of n, ni, . . ., then a belongs to
the exponent t modulo p = q^qi^' . . . , and a' — 1 is divisible by q only h times.

Let the period of the pure decimal fraction for a/h have 2n digits. If
h is prime to 10" — 1, the sum of corresponding digits in the half periods is
always 9, and the sum of corresponding remainders is h. Next, let 6 and
10" — 1 have d>l as their g. c. d. and set h' = h/d. Let a„ be the nth re-
mainder in finding the decimal fraction. Then a+a„ = 6'A:, ai+a„+i = 6'/ci,
etc. The sums q-\-qn, 5i+g„+i, ... of corresponding digits in the half
periods equal

{\{)k-k^)/d, il0k,-k2)/d,.. ., {10k,_r-k)/d.

Similar results hold when the period of mn digits is divided into n parts of
m digits each. For example, in the period

002481389578163771712158808933
for 1/403, the two halves are not complementary (10^^ — 1 being divisible
by 31); for i = l, 2, 3, the sum of the digits of rank i, i-\-3, i+6, . . ., i+27
is always 45, while the corresponding sums of the remainders are 2015.

N. Druckenmiiller^^" noted that any fraction can be expressed as a/x-\-
ai/x^-l- ....

J. Westerberg^^ gave in 1838 factors of 10"± 1 for nS 15.

G. R. Perkins^^ considered the remainder r^ when N'^ is divided by P,
and the quotient q in Nrj._i = Pqx-\-rj.. If Tk'^P—l, there are 2k terms in
the period of remainders, and

rk+x+r^ = P, qk+x+qx = N-l.

[These results relate to 1/P written to the base N.]

^^Polytechnisches Journal (ed., J. G. Dingier), Stuttgart, 34, 1829, 68; extract from Mechanics'

Magazine, N. 313, p. 411.
^*Von den Perioden der Decimalbriiche, Progr., Oels, 1834.

'^'De quelques propriet^s des nombres et des fractions d^cimales p^riodiques, Nantes, 1836,21 pp.
""T.heorie der Kettenreihen . . ., Trier, 1837.
28See Chapter on Perfect Numbers."*
2»Amer. Jour. Sc. Arts, 40, 1841, 112-7.

164 History of the Theory of Numbers. [Chap, vi

E. Catalan^" converted periodic decimals into ordinary fractions without
using infinite progressions. When 1/13 is converted into a decimal, the
period of remainders is 1, 10, 9, 12, 3, 4; repeat the period; starting in
the series of 12 terms with any term (as 10), take the fourth term (4) after
it, the fourth term (12) after that, etc.; then the sum 26 of the three is a
multiple of 13. In general, if D is a prime and D — l=mn, the sum of n
terms taken w by m in the period for N/D is a multiple of D [cf. Thibault'^].

If the sum of two terms of the period of remainders for N/D is D, the
same is true of the terms following them. Hence the sum of corresponding
terms of the two half periods is D. This happens if the number of terms
of the period is <f){D).

Thibault^^ denoted the numbers of digits in the periods for l/d and
1/d' by m and m'. If d' is divisible by d, m' is divisible by m. If d and d'
have no common prime factor other than 2 or 5, the number of digits in
the period for \/dd' is the 1. c. m. of m, m'. Hence it suffices to know the
length of the period for 1/p", where p is a prime. If 1/p has a period of m
digits and if 1/p" is the last one of the series 1/p, 1/p^, . . . which has a
period of m digits, then the period for 1/p" for a >n has mp"'^ digits. For
p = 3, we have w = 2; hence 1/3'^ for r^2 has a period of y~^ digits. For
any prime p for which 7^p^ 101, we have n = 1, so that 1/p" has a period
of mp°-~^ digits. Note that \/p and 1/p^ have periods of the same length
to base h if and only if h^~^ = 1 (mod p^). Proof is given of Catalan's^" first
theorem, which holds only when 10"' ^1 (mod D), i. e., when m is not a
multiple of the number of digits in the period. For example, the sum of
the /cth and (6+A;)th remainders for 1/13 is not a multiple of 13.

E. Prouhet^^ proved Thibault's" theorem on the period for l/p". He^^"
noted that multiples of 142857 have the same digits permuted.

P. Lafitte^^ proved Midy's^^ theorem that, if p is a prime not dividing
m and if the period for m/p has an even number of digits, the sum of the
two halves of the period is 9 ... 9.

J. Sornin^^ investigated the number m of digits in the period for 1/Z),
where D is prime to 10. The period is a; = (10"* - l)/D. First, let D = lOA: + 1 .
Then x = \Qy — \, where

10*"-^+ A; ,^ , , lO'-^-A:^
y = ^ = lOz+k, z =

Finally, we reach v= \l — { — k)'^\/D, and x is an integer if and only if v
is. Hence if we form the powers of the number k of tens in D, add 1 to
the odd powers, but subtract 1 from the even powers of k, the first exponent
giving a result divisible by D is the number m of digits in the period.

»»Nouv. Ann. Math., 1, 1842, 464-5, 467-9.

*nhid., 2, 1843, 80-89.

"/bid., 5, 1846, 661.

^IhU., 3, 1844, 376; 1851, 147-152.

'Vbid., 397-9. Cf. Araer. Math. Monthly, 19, 1912, 130-2.

w/Wd., 8, 1849, 50-57.

Chap. VI] PeEIODIC DECIMAL FRACTIONS. 165

Next, if D = 10k — 1, we have a like rule to be applied only to the ^"^ — 1. If
D = 10k=^3, 1/(3Z)) has a denominator lOZ^l, and the length of its period,
found as above, is shown to be not less than that for 1/D.

Th. Bertram^^ gave certain numbers p for which l/p has a given
length k of period for k^ 100. Cf. Shanks.^^

J. R. Young^^ took a part of a periodic decimal, as .1428571 428 for 1/7,
and marked off from the end a certain number (three) of digits. We can
find a multipHer (as 6) such that the product, with the proper carrying
(here 2) from the part marked off, has all the digits of the abridged number
in the same cyclic order, except certain of the leading digits. In the special
case the product is .8571428.

W. Loof" gave the primes p for which the period for l/p has a given
number n of digits, n^ 60, with no entry for n = 17, 19, 37-40, 47, 49, 57, 59,
and with doubt as to the primality of large numbers entered for various
other n's.

E. Desmarest^^ gave the primes P< 10000 for which 10 belongs to the
exponent {P — l)/t for successive values of t. The table thus gives the
length of the period for 1/P. He stated (pp. 294-5) that if P is a prime
< 1000, and if p is the length of the period for A/P, then except for P = 3
and P = 487 the length of the period for A/P^ is pP.

A. Genocchi^^ proved Euler's^^ rule by use of the quadratic reciprocity
law. Thus 5 is a quadratic residue or non-residue of N according as
N = 5m=^l or 5m±3; for 4n+l = 5m='=l, n or n — 2 is divisible by 5; for
4n — l = 5m='=l, n or n-\-2 is divisible by 5. Also, 2 is a residue of 4n±l
for n even, a non-residue for n odd. Hence 10 is a residue of A^ = 4n='= 1 for
n even if n orn =f2 is divisible by 5, and for n odd if neither is. Thus Euler's
inclusion of n=F6 is superfluous. By a similar proof, 10 is quadratic non-
residue of A/' = 4n±l if both 2 and 5 occur among the divisors of n±2,
n±6, or if neither occurs; a residue if a single one of them occurs.

A. P. Reyer^^" noted that the period for a/3^ has 3^~^ digits and gave the
length of the period for a/p for each prime p< 150.

*F. van Henekeler^^^ treated decimal fractions.

C. G. Reuschle^" gave for each prime p< 15000 the exponent e to which
10 belongs modulo p. Thus e is the length of the period for l/p. He gave
all the prime factors of lO'^-l for n^l6, n = lS, 20, 21, 22, 24, 26, 28, 30,
32, 36, 42; those of 10"+1 for n^l8, n = 21; also cases up to n = 243 of
the factors of the quotient obtained by excluding analytic factors.

"Einige Satze aus der Zahlenlehxe, Progr. Coin, Berlin, 1849, 14-15.

»«London, Ed. Dublin Phil. Mag., 36, 1850, 15-20.

»^Archiv Math. Phys., 16, 1851, 54-57. French transl. in Nouv. Ann. Math., 14, 1855, 115-7.

Quoted by Brocard, Mathesis, 4, 1884, 38.
'^Th^orie des nombres, Paris, 1852, 308. For errata, see Shanks*^ and G^rardin.^'^
"Bull. Acad. Roy. Sc. Belgique, 20, II, 1853, 397-400.
"<^Archiv Math. Phys., 25, 1855, 190-6.
'^''Ueber die primitiven Wurzeln der Zahlen und ihre Anwendung auf Dezimalbriicbe, Leyden,

1855 (Dutch).
"Math. Abhandlung.. .Tabellen, Progr. Stuttgart, 1856. Full title in Ch. I."* Errata,

Bork,i''5 Hertzer,ii3 Cunningham. i"

I

166 History of the Theory of Numbers. [Chap, vi

W. Stammer^^ noted that n/p = 0.di . . . a^ implies

-(10'-l)=ai...a,.
V

J. B. Sturm^^ used this result to explain the conversion of decimal into
ordinary fractions without the use of series.

M. Collins'^^ stated that, if we multiply any decimal fraction having m
digits in its period by one with n digits, we obtain a product with Own
digits in its period if vi is prime to n, but with 71(10™ — 1) digits if n is
divisible by m.

J. E. Oliver^^ proved the last theorem. If x'/x gives a periodic fraction
to the base a with a period of ^ figures, then a^ = 1 (mod x) and conversely.
The product of the periodic fractions for x'/x, . . . , z'/z with period lengths
^, . . . , f has the period length

•M(^,...,f),

M{x,...,z)

where M{x, . . ., z) is the 1. c. m. of x, . . . , z. He examined the cases in
which the first factor in the formula is expressible in terms of ^, . . . , f .

Fr. Heime'*^ and M. Pokorny^^ gave expositions without novelty.

Suffield*^ gave the more important rules for periodic decimals and indi-
cated the close connection with the method of synthetic division.

W. H. H. Hudson*^ called d a proper prime if the period for n/d has d — 1
digits. If the period for r/p has n = ip — l)/\ digits, there are X periods
for p. The sum of the digits in the period for a proper prime p is 9{p — 1)/2.
If 1/p has a period of 2n digits, the sum of corresponding digits in the two
half periods is 9, and this holds also if p is composite but has no factor
dividing 10" — 1 [Midy"]. If lOp+l is a proper prime, each digit 0, 1, . . . , 9
occurs p times in its period. If a, h are distinct primes with periods of
a, /3 digits, the number of digits in the period for ab is the 1. c. m. of a, /8
[Bernoulli^]. Let p have a period of n digits and l/p = A-/(10" — 1). Let m
be the least integer for which

\ljp^-'^\2)p^-''^- ^\x-l) p
is an integer; then 1/p^ has a period of mn digits.

"Archiv Math. Phys., 27, 1856, 124.

«/6id., 33, 1859, 94-95.

«Math. Monthly (ed., Runkle), Cambridge, Mass., 1, 1859, 295.

**Ibid., 345-9.

♦'Ueber relative Prim- und correspondirende Zahlen, primitive und sekundare Wurzeln und

periodische Decimalbriiche, Progr., BerUn, 1860, 18 pp.
"Ueber einige Eigenschaften periodischer Dezimalbriiche, Prag, 1864.
♦^Synthetic division in arithmetic, with some introductory remarks on the period of circulating

decimals, 1863, pp. iv-|-19.
*80xford, Cambridge and Dublin Messenger of Math., 2, 1864, 1-6. Glaisher" atrributed this

useful anonymous paper to Hudson.

Chap. VI] PERIODIC DECIMAL FRACTIONS. 167

V. A. Lebesgue^^ gave for iV^347 the periods for 1/iV, r/N,. . .[cf.
Gauss^l.

Sanio^° stated that, if m, n,. . . are distinct primes and 1/m, 1/n, . . .
have periods of length q, q',. . ., then l/(wV. . .) has the period length
^a-i^b-i qq' ^ He gave the length of the period for l/p for each
prime p^700, and the factors of 10" — 1, n^ 18.

F. J. E. Lionnet^^ stated that, if the period for a/h has n digits, that for
any irreducible fraction whose denominator is a multiple of h has a multiple
of n digits. If the periods for the irreducible fractions a/6, a'/h', . . . have
n, n', . • • digits, every irreducible fraction whose denominator is the 1. c. m.
of b, h',. . . has a period whose length is the 1. c. m. of n,n',. . .. If the period
for 1/p has n digits and if p" is the highest power of the prime p which divides
10" — 1, any irreducible fraction with the denominator p"'^^ has a period
of np^ digits.

C. A. Laisant and E. Beaujeux^^ proved that if g is a prime and the
period for 1/q to the base B is P = ab. . .h, with q — 1 digits, then

P-{a+h+...+h) = {B-l)a, ^{^+^-y) =

B'-'-l

and stated that a like result holds for a composite number q if we replace
q—1 by/=</)(g). Their proof of the generaUzed Fermat theorem 5^=1
(mod q) is quoted under that topic.

C. Sardi^^ noted that if 10 is a primitive root of a prime p = lOn+1, the
period for 1/p contains each digit 0,..., 9 exactly n times [Hudson^^].
For p = 10n-f-3, this is true of the digits other than 3 and 6, which occur
n+1 times. Analogous results are given for lOn+7, lOn+9.

Ferdinand Meyer^^ proved an immediate generalization from 10 to
any base k prime to 6, 6', ... of the statements by Lionnet.^^

Lehmann^" gave a clear exposition of the theory.

C. A. Laisant and E. Beaujeux^^ considered the residues Vq, ri, . . . when
A, AB, AB^,. . . are divided by A- Let ri_iB = QiZ)i+r,. When written
to the base B, let Di = ap. . .02^1, and set Di = ap. . Mi. Then

airi+ . . . +0prp = Z)i(ri-Q2A- • • • -QpDp).

The further results are either evident or not novel.

For G. Barillari^°" on the length of the period, see Ch. VII.

*'M6m. soc. sc. phys. et nat. de Bordeaux, 3, 1864, 245.

^"Ueber die periodischen Decimalbrtiche, Progr., Memel, 1866.

"Algebre 61em., ed. 3, 1868. Nouv. Ann. Math., (2), 7, 1868, 239. Proofs by Morel and Pellet,

(2), 10, 1871, 39-42, 92-95.
MNouv. Ann. Math., (2), 7, 1868, 289-304.
"Giornale di Mat., 7, 1869, 24-27.
"Archiv Math. Phys., 49, 1869, 168-178.

""Ueber Dezimalbriiche, welche aus gewohnUchen Briichen abgeleitet sind, Progr., Leipzig, 1869.
66N0UV. Ann. Math., (2), 9, 1870, 221-9, 271-281, 302-7, 354-360.

168 History of the Theory of Numbers. [Chap, vi

*Th. Schroder^^ and J. Hartmann^^ treated periodic decimals.

W. Shanks^^ gave Lambert's method (Bernoulli,^ end) for shortening
the work of finding the length of the period for 1/A^.

G. Salmon^^ remarked that the number 71 of digits in the period is known
if we find two remainders which are powers of 2, since 10" = 2'' and 10'' = 2'
imply 10"^"''^= 1; also if we find three remainders which are products of
powers of 2 and 3. Muir''^ noted that it is here impUed that aq — bp equals
n, whereas it is merely a multiple of n.

J. W. L. Glaisher^" proved that, for any base r,

1

ir-iy

.012...r-3r-l,

a generalization of 1/81 = .012345679.

W. Shanks^^ gave the length of the period for 1/p, when p is a prime
< 30000, and a list of 69 errors or misprints in the table by Desmarest,^^
and 11 in that by Burckhardt.^°

Shanks^- gave primes p for which the length n of the period for 1/p is a
given number ^ 100, naturally incomplete. Shanks^^ gave additional
entries p for n = 26, ?7 =99; noted corrections to his former table and stated
that he had extended the table to 40000. Shanks^^ mentioned an extension
in manuscript from 40000 to 60000. An extension to 120000 in manu-
script was made by Shanks, 1875-1880. The manuscript, described by
Cunningham, ^-^ who gave a list of errata, is in the Archives of the Royal
Society of London.

Shanks®^ stated that if a is the length of the period for 1/p, where p is a
prime >5, that for 1/p'* is ap""'^ [^vithout the restriction by Thibault,^^
Muir^^].

G. de Coninck^® stated that, if the last digit (at the right) of A is 1 or 9,
the last digit of the period for 1/A is 9 or 1 ; while, if A is a prime not ending
in 1 or 9, its last digit is the same as the last in the period.

Moret-Blanc^^ noted that the last property holds for any A not divisible
by 2 or 5. For, if a is the integer defined by the period for 1/A, that for
{A — l)/A is {A — l)a, whence a+ (A — 1)0 = 10" — 1, if n is the length of the
periods. He noted corrections to the remaining nine laws stated by Coninck
and implied that when corrected they become trivial or else known facts.

"Progr. Ansbach, 1872,

"Progr. Rinteln, 1872.

"Messenger Math., 2, 1873, 41-43.

"/bid., pp. 49-51, 80.

^^Ibid., p. 188.

«iProc. Roy. Soc. London, 22, 1873-4, 200-10, 384-8. Corrections by Workman.*"

"/bwi., pp. 381^. Cf. Bertram", Loof."

*Hbid., 23, 1874-5, 260-1.

^Ibid., 24, 1875-6, 392.

"Messenger Math., 3, 1874, 52-55.

"Nouv. Ann. Math., (2), 13, 1874, 569-71; errata, 14, 1875, 191-2.

*Ubid., (2), 14, 1875, 229-231.

Chap. VI] PERIODIC DECIMAL FRACTIONS. 169

Karl Broda^^ considered a periodic decimal fraction F having an even
number r of digits in the period and a number m of p digits preceding the
period. Let x be the first half of the period, y the second half. Then

10"* 10"*+'" 10"'+^'" io"'+3^^- ■"10"' ' 10'"(102'"-1)

_9(jp40'"+a;+p)+q
9-10"'(10^+l)

ifx+2/ = o(10'' — l)/9 = a...a(tor terms). The first paper treated the case
p = m = 0, and gave the generalization to base a in place of 10:

£ ,^ , _£ , a+(a-l)x -r , _ a'-l

a^^a"-^a'''^-- ' " (a-l)(a'-+l) " ^+2/-^ ^_j-

The case a = a — l shows that a purely periodic fraction to the base a equals
(a:+l)/(a'"+l) if the sum of the half periods has all its digits (to base a)
equal to a— 1. Returning to the base 10, and taking A'= 9(10'"H-1),
Z = 9x+a, where each digit of x is ^a, we see that Z/N equals a decimal
fraction in which x is the first half of the period of r digits, while the second
half is such that the sum of corresponding digits in it and x is a. If R is the
remainder after r digits of the period have been obtained, R-\-Z = a (10''+ 1).

C. G. Reuschle^^ gave tables which serve to find numbers belonging to
a given exponent < 100 with respect to a given prime modulus < 1000.

P. Mansion''" gave a detailed proof that, if n is prime to 2, 3, 5, and if
the period for 1/n has n — 1 digits, the sum of corresponding digits in the
half periods is 9.

T. Muir^^ proved that, if p is a prime, either of

N' = 1 (mod f) , iV^P" = 1 (mod p''+")

follows from the other. If Xi is the least positive integer x for which the
first holds and if p' is the highest power of p dividing N""' — !, then Xip" is
the least positive integer y for which N^ = l (mod p'+"). Hence the known
theorem: If N=JIpi'^, where Pi,P2,-- are distinct primes, and if the period
for \/pi has m^ digits, and if Pi' is the highest power of Pi dividing 10"^ — 1,
the number of digits in the period for \/N is the 1. c. m. of the niip^^i'^*. He
asked if 6 = 1 when p>3, as affirmed by Shanks.^^

Mansion's proof {ibid., 5, 1876, 33) by use of periodic decimals of the
generalized Fermat theorem is quoted under that topic.

D. M. Sensenig'^ noted that a prime p?^2, 5, divides iV if it divides the
sum of the digits of N taken in sets of as many figures each as there are
digits in the period for l/p.

«»Archiv Math. Phys., 56, 1874, 85-98; 57, 1875, 297-301.

"Tafeln complexer Primzahlen, Berlin, 1875. Errata by Cunningham, Mess. Math., 46,

1916, 60-1.
'"Nouv. Corresp. Math., 1, 1874-5, 8-12.
"Messenger Math., 4, 1875, 1-5.
"The Analyst, Des Moines, Iowa, 3, 1876, 25.

i

170 History of the Theory of Numbers. [Chap, vi

*A. J. M. Brogtrop^' treated periodic decimals.

G. Bellavitis^* noted that the use of base 2 renders much more com-
pact and convenient Gauss' ^^ table and hence constructed such a table.

W. Shanks'^ found that the period for 1/p, where p = 487, is divisible
by p, so that the period for 1/p^ has p — l digits.

J. W. L. Glaisher^^ formed the period 05263. . . for 1/19 as follows:
List 5; divide it by 2 and list the quotient 2; since the remainder is 1,
divide 12 by 2 and list the quotient 6; divide it by 2 and list the quotient,
etc. To get the period for 1/199, start with 50. To get the period, apart
from the prefixed zero, for 1/49, start with 20 and divide always by 5; for
1/499, start wath 200.

Glaisher^^ noted that, if we regard as the same periods those in which
the digits and their cyclic order are the same, even if commencing at differ-
ent places, a number q prime to 10 will have/ periods each of a digits, where
af=4){q). This was used to check Goodwyn's table. ^^ If g = 39, there are
four periods each of six digits, li q — 1 belongs to the period for 1/q, the
two halves of every period are complementary; if not, the periods form
pairs and the periods in each pair are complementary. For each prime
N< 1000, except 3 and 487, the period for l/N" has nA^*"^ digits if that
for 1/iV has n digits.

Glaisher'^^ collected various known results on periodic decimals and
gave an account of the tables relating thereto. If q is prime to 10 and if
the period for 1/q has (/)(g) digits, the products of the period by the 4>{q)
integers <q and prime to q have the same digits in the same cyclic order;
for example, if g = 49. He gave (pp. 204-6) for each g<1024 and prime
to 10 the number a of digits in the period for 1/q, the number n of periods
of irreducible fractions p/q, not regarding as distinct two periods having
the same digits in the same cychc order, and, finally Euler's (f>(,q). The
values of a and n were obtained by mere counting from the entries in Good-
wyn's^^ "table of circles"; in every case, an = <j){q). For the prime p = 487,
he gave the full periods for 1/p and 1/p", each of 486 digits, thus verifying
Desmarest's^^ statement of the exceptional character of this p [cf. Shanks'^].

Glaisher^^ again stated the chief rules for the lengths of periods.

The problem was proposed^" to find a number whose products by 2, . . . , 6
have the same digits, but in a new order.

Birger Hausted^^ solved this problem. Start with any number a of
one digit, multiply it by any number p and let b be the digit in the units

"Nieuw Archief voor VViskunde, Amsterdam, 3, 1877, 58-9.

7«Atti Accad. Lincei, Mem. Sc. Fis. Mat., (3), 1, 1877, 778-800. Transunti, 206. See 62a

of Ch. VII.
"Proc. Roy. Soc. London, 25, 1877, 551-3.
^^Messenger Math., 7, 1878, 190-1. Cf. Desmarest."
"Report British Assoc, 1878, 471-3.
"Proc. Cambridge Phil. Soc, 3, 1878, 185-206.

"Solutions of the Cambridge Senate-House Problems and Riders for 1878, pp. 8-9.
""Tidsskrift for Math., Kjobenhavn, 2, 1878, 28.
"/bid., pp. 180-3. Jornal de Sc. Math, e Ast., 2, 1878, 154-6.

Chap. VI] PeEIODIC DECIMAL FRACTIONS. 171

place of the product ap, /S the digit in the tens place. Write the digit b
to the left of digit a to form the last two digits of the required number P.
The number c in the units place in 6p+j8 is written to the left of digit h in
P. To cp add the digit in the tens place of bp and place the unit digit of
the sum to the left of c in P. The process stops with the kth. digit t if the
next digit would give a. Then P = t. . . cba and its products by k integers or
fractions has the same k digits in the same cyclic order. For a = 2, p = 3,
we get A; = 28 and see that P is the period of 2/27, and the k multipliers
are m/2, m = l,. . ., 28. [To have an example simpler than the author's,
take a = 7, p = 5; then P = 142857, the period of 1/7; the multipliers are
1, . . . , 6.] For proof, we have

P = 10''-H-\- . . .-\-10h+10b+a, pP = 10''-'a+10''-H+ . . .+10c-\-h,

pP = 10^-a+^, 10^ = 10^'

so that P is the period with k digits for a/{lOp — l).

E. LucasS2 gave the prime factors of lO'^^l, 10'^±1, lO^^^l, 10^^+1,
10^^+1, communicated to him by W. Loof, with the remark that (10^^ — 1)/9
has no prime factor < 3035479. Lucas gave the factors of 10^^+1.

J. W. L. Glaisher^^ proved his^^ earlier statements, repeated his" earher
remarks, and noted that, if g is a prime such that the period for 1/q has q — 1
digits, the products of the period for 1/q by 1, 2, . . ., g — 1 have the same
digits in the same cyclic order. This property, well known for q = 7, holds
also for g = 17, 19, 23, 29, 47, 59, 61, 97 and for q = 7\

0. Schlomilch^^ stated that, to find every N for which the period for
1/N has 2k digits such that the sum of the sth and (fc+s)th digits is 9 for
s = 1, . . . , A;, we must take an integer iV= (10*^+l)/r; then the first k digits
of the period are the k digits of T — 1.

C. A. Laisant^^ extended his investigations with Beaujeux^^'^^ and gave a
summary of known properties of periodic fractions; also his^^ process to
find the period of simple periodic fractions without making divisions.

V. Bouniakowsky^^ noted that the property of the period of 1/N,
observed by Schlomilch^^ for iV = 7, 11, 13, 77, 91, 143, holds also for the pe-
riods of /c/iV, for A; = iV — 1 and (iV — 1)/2, with the same values of AT. Consider
the decimal fraction Q.yiy2- ■ ■ with ym — ym-i+ym-2 (mod 9), replacing any
residue zero by 9, and taking yi > 0, 1/2 > 0- The fraction is purely periodic
and is either 0.9 or 0.33696639 or has the same digits permuted cyclically,
or else has a period of 24 digits and begins with 1, 1 or 2, 2 or 4, 4, or has the
same 24 digits permuted cyclically or by the interchange of the two halves

s^Nouv. Corresp. Math., 5, 1879, 138-9.

8'Nature, 19, 1879, 208-9.

s^Zeitschrift Math. Phys., 25, 1880, 416.

8*M6m. Soc. Sc. Phys. et Nat. de Bordeaux, (2), 3, 1880, 213-34.

86Le8 Mondes, 19, 1869, 331.

"BuU. Acad. Sc. St. P^tersboiirg, 27, 1881, 362-9.

172 History of the Theory of Numbers. [Chap, vi

of the period. The property of Schlomilch holds for these and the generali-
zation to any base, as well as for those with the law xjm = '^ym-\-\-ym-2' But if

ym = ^ym-i-2y^.2 (mod 9), ?/. = (2"'-'-l)(!/2-2/i)+2/i (mod 9),

the fact that 2^ = 1 (mod 9) shows that the period has at most six digits.
Those with six reduce by cychc permutation to nine periods :
167943, 235986, 278154, 197346,
265389, 218457, 764913, 329568, 751248.

In the A-th of these the sum of corresponding digits in the two half periods
is always =A- (mod 9).

Karl Broda^^ examined for small values of r and certain primes p the
solutions a: of x''= 1 (mod p) to obtain a base x for which the periodic frac-
tion for 1/p has a period of r digits, and similariy the condition x^=—\
(mod p) for an even number of digits in the period (Broda^^).

F. Kessler^^ factored 10"-1 forn = ll, 20, 22, 30.

W. W. Johnson^° formed the period for 1/19 by placing 1 at the extreme

right, next its double, etc., marking wdth a star a digit when there is 1 to carry:

« * * * * * * ««

05263157894736842 1. ;^

To deduce the value of 1/19 written to the base 2, use 1 for each digit
starred and 0 for the others, reversing the order:

.6 0001101011110010 i.

If we apply the first process with the multipUer m, we get the period for the
reciprocal of 10?7i — 1.

E. Lucas^^ gave the prime factors of 10" — 1 for n odd, n^l7, 7i = 21,
and certain factors forn = 19, . . . , 41 ; those of 10" + 1 for n^ 18 and n = 21.
He stated that the majority of the results were given by Loof and pubUshed
by Reuschle. In 1886, Le Lasseur gave

10^7-1 =3--2071723-5363222[3]57,

said by Loof to have no divisor < 400,000 other than 3,9. On the omission
of the digit 3, see Cunningham. ^-^

F. Kessler^- listed nine errors in Burckhardt's-" table and described his
own manuscript of a table to p = 12553, i. e., for the first 1500 primes.

Van den Broeck^^ stated that 10^" -1 is divisible by 3"+^
A. Lugli^^ proved that, if p is a prime 5^2, 5, the length of the period
of 1/p is a divisor of p — 1. If the number of digits in the period of a/p is
an even number 2t, the ^th remainder on dividing a by p is p — 1, and con-
versely. Hence, if r^ is the hth remainder, rh+rh+i = p {h = l,. . ., t), and
the sum of all the r's is tp. If the period of 1/p has s digits, s<p — 1, then

".\rchiv Math. Phys., 68, 1882, 85-99.

«»Zeitschrift Math. Naturw. Unterricht, 15, 1884, 29.

•"Messenger of Math., 14, 1884-5, 14-18.

"Jour, de math. 6Um., (2), 10, 1886, 160. Cf . rinterm^diaire des math., 10, 1903, 183. Quoted

by Brocard, Mathesis, 6, 1886, 153; 7, 1887, 73 (correction, 1889, 110).
"Archiv Math. Phys., (2), 3, 1886, 99-102.

"Mathesis, 6, 1886, 70. Proofs, 23.5-6, and Math. Quest. Educ. Times, 54, 1891, 117.
"Periodico di Mat., 2, 1887, 161-174.

Chap. VI] PERIODIC DECIMAL FRACTIONS. 173

p — l=sh and we have h sets of s fractions whose periods differ only by the
cycHc permutation of the digits. If p is a product of distinct primes pi, P2 • • •
and if the lengths of the periods of 1/p, 1/pi, l/p2, ■ ■ ■ are s, Si, S2, . . . , then
s is the 1. c. m. of Si, S2,.... If p = Pi"P2^- • •> and s, Si, s' are the lengths of
the periods of 1/p, 1/pi, l/pi", then s' is one of the numbers Si, Sip,. . .,
SiPi°~^ and hence divides (pi — l)pi"~^; and s is a divisor of <f){p). Thus p
divides lO^^^^-l.

C. A. Laisant^^ used a lattice of points, whose abscissas are a+r,a-\-2r,...,
a-\-pf and ordinates are their residues <p modulo p, to represent graphically
periodic decimal fractions and to expand fractions into a difference of two
series of ascending powers of fixed fractions.

*A. Rieke^® noted that a periodic decimal with a period of 2m digits equals
(i4. + l)/(10"*+l), where A is the first half of the period. He discussed the
period length for any base.

W. E. HeaP^ noted that, if B contains all the prime factors of N, the
number of digits in the fraction to the base B for M/N is the greatest integer
in (n+n' — l)/n', where n—n' is the greatest difference found by subtracting
the exponent of each prime factor of N from the exponent of the same prime
factor of B. If B contains no prime factor of N, the fraction for M/N is
purely periodic, with a period of ^(A'') digits. If B contains some, but not
all, of the prime factors of N, the number of digits preceding the period is
the same as in the first theorem. The proofs are obscure. There is given
the period for 1/p when p<100 and has 10 as a primitive root [the same
p's as by Glaisher^^]. Likewise for base 12, with p<50.

R. W. Genese^^ noted that, if we multiply the period for 1/81 [Glaisher^"]
by m, where m<81 and prime to it, we get a period containing the digits
0, 1, . . ., 9 except 9n—m, where 9n is the multiple of 9 just exceeding m.

Jos. Mayer^^ investigated the moduli with respect to which 10 belongs
to a given exponent, and gave the factors of 10"— 1, n< 12. He discussed
the determination of the exponent to which 10 belongs for a given modulus
by use of the theory of indices and by the methods of quadratic, cubic,
biquadratic,... residues. He used also the fact that there are (a — a')
08-/3') . . . divisors of Pi''p2^Vz ■ ■ • which divide no one of the fixed factors
ViVVi ■ • ■, Pi>2W> • • • J where a<a,b<^,..., and pi, P2,-- are distinct
primes. He gave the length of the period for 1/p, for each prime p^2543
and 22 higher primes [Burckhardt^^].

L. Contejean^°° proved that, in the conversion of an irreducible fraction
a/h into a decimal fraction, if the remainders o^ and a^ are congruent
modulo b, so that lO'a^lO^'a, then 10"'~''-1 is divisible by the quotient
h' of b by the highest factor 2*5' of b. Thus the length of the period is

"Assoc, fran?. avanc. sc, 16, 1887, II, 228-235.

•'Versuch iiber die periodischen Bniche, Progr., Riga, 1887.

•^Annals of Math., 3, 1887, 97-103.

•^Report Britiah Assoc, 1888, 580-1.

"Ueber die Grosse der Periode eines unendlichen Dezimalbruches, oder die Congruence

lO^Sl (mod P). Progr. K. Studienanstalt Burghausen, Munchen, 1888, 52 pp.
""Bull. Boc. philomathique de Paris, (8), 4, 1891-2, 64-70.

174 History of the Theory of Numbers. [Chap, vi

m—r, while r digits precede the period. The condition that the length of
the period be the maximum 0(6') is that 10 be a primitive root of h', whence
5' = p", since 6'?^ 4 or 2^", p being an odd prime.

P. Bachmann^°^ used a primitive root g of the prime p and set

to the base g. We get the multiples Q, 2Q, . . . , (p — 1)Q by cyclic permuta-
tion of the digits of Q. For p = 7, ^ = 10, Q = 142857.

J. Kraus^"^ generaUzed the last result. When ri/n is converted into a
periodic fraction to base g, prime to n, let ai, . . . , Ck be the quotients
and ri, . . . , r^ the remainders. Then

<7*-l

rx = ax^^"^+ax+i/"^+- • -f«x-i (X = l,. • ■, k),

n

whence

^x(aiS'*"^+ • • • +(ik) =n(«x9'*"^+ • ■ • 4-ax-i).

In particular, let n be such that it has a primitive root g, and take ri = 1.

Then

ft

and if rx is prime to n, the product ry,Q has the same digits as Q permuted
cyclically and beginning with a^.

H. Brocard^"^ gave a tentative method of factoring 10" — 1.

J. Mayer^°^ gave conditions under which the period of z/P to base a,
where z and a are relatively prime to P, shall be complete, i. e., corresponding
digits of the two halves of the period have the sum a — 1.

Heinrich Bork^°^ gave an exposition, without use of the theory of num-
bers, of kno^n results on decimal fractions. There is here first published
(pp. 36-41) a table, computed by Friedrich Kessler, showing for each prime
p< 100000 the value of q={p — l)/e, where e is the length of the period
for 1/p. The cases in which ^ = 1 or 2 were omitted for brevity. He
stated that there are many errors in the table to 15000 by Reuschle.'*"
Cunningham^^^ listed errata in Kessler's table.

L. E. Dickson^"^ proved, without the use of the concept of periodic
fractions, that every integer of D digits written to the base N, which is
such that its products by D distinct integers have the same D digits in
the same cyclic order, is of the form A{N^ — 1)/P, where A and P are
relatively prime. A number of this form is an integer only when P is prime

"iZeitschrift Math. Phys., 36, 1891, 381-3; Die Elemente der Zahlentheorie, 1892, 95-97.

Alike discussion occurs in l'interm(5diaire des math., 5, 1898, 57-8; 10, 1903, 91-3.
"'Zeitschrift Math. Phys., 37, 1892, 190-1.
"'El Progreso Matematico, 1892, 25-27, 89-93, 114-9. Cf. rinterm^diaire des math., 2, 1895,

323-4.
'"Zeitschrift Math. Phys., 39, 1894, 376-382.

losperiodische Dezimalbriiche, Progr. 67, Prinz Heinrichs-Gymn., Berlin, 1895, 41 pp.
looQuart. Jour. Math., 27, 1895, 366-77.

Chap. VI] PERIODIC DECIMAL FRACTIONS. 175

to N, and D is a multiple of the exponent d to which N belongs modulo P.
The further discussion is limited to the case D = d, to exclude repetitions
of the period of digits. Then the multipUers which cause a cyclic permuta-
tion of the digits are the least residues of N, N^, . . . , A^^ modulo P. For
A = 1, we have a solution for any N and any P prime to N. There are listed
the 19 possible solutions with A>1, N^QS, and having the first digit >0.
The only one with A^= 10 is 142857. General properties are noted.

A like form is obtained (pp. 375-7) for an integer of D digits written to
the base A^, such that its quotients by D distinct integers have the same
D digits in the same cyclic order. The divisors are the least residues of
N^, N^-\. . ., N modulo P. For example, if N = n, P = 7, A=4:, we get
4(11^ — 1)/7, or 631 to base 11, whose quotients by 2 and 4 are 316 and 163,
to base 11. Another example is 512 to base 9.

E. Lucas^ gave all the prime factors of 10"— 1 forn^ 18.

F. W. Lawrence^"^ proved that the large factors of 10^^ — 1 and 10^^ — 1
are primes.

C. E. Bickmore^'^^ gave the factors of 10" -1, n^ 100. Here (1023-l)/9
is marked prime on the authority of Loof , whereas the latter regarded its
composition as unknown [Cunningham^^^]. There is a misprint for 43037
in 10^^-1.

B. Bettini^"^ considered the number n of digits in the period of the deci-
mal fraction for a/b, i. e., the exponent to which 10 belongs modulo h. If
10 is a quadratic non-residue of a prime b, n is even, but not conversely
(p. 48). There is a table of values of n for each prime 6^277.

V. Murer^^" considered the n = mq remainders obtained when a/b is
converted into a decimal fraction with a period of length n, separated them
into sets of m, starting with a given remainder, and proved that the sum
of the sets is a multiple of 9 ... 9 (to m digits) . Further theorems are found
when q = l, 2 or 3.

J. Sachs ^^^^ tabulated all proper fractions with denominators <250 and
their decimal equivalents.

B. Reynolds^ ^^ repeated the rules given by Glaisher'^^' '^^ for the length
of periods. He extended the rules by Sardi^^ and gave the number of times
a given digit occurs in the various periods belonging to a denominator N,
both for base 10 and other bases.

Reynolds^^^ gave numerical results on periodic fractions for various
bases the lengths of whose period is 3 or 6, and on the length of the period for
1/A^ for every base <N—1, when A^ is a prime.

A. Cunningham^ ^^ applied to the question of the length of the period
of a periodic fraction to any base the theory of binomial congruences [see

i"Proc. London Math. Soc, 28, 1896-7, 465. Ci. Bickmore" of Ch. XVI.

"'Nouv. Ann. Math., (3), 15, 1896, 222-7.

"Teriodico di Mat., 12, 1897, 43-50. "o/bid., 142-150.

uoaprogr. 632, Baden-Baden, Leipzig, 1898.

""Messenger Math., 27, 1897-8, 177-87.

»"/feid., 28, 1898-9, 33-36, 88-91.

"'/bid., 29, 1899-1900, 145-179. Errata.i"

176 History of the Theory of Numbers. [Chap.vi

201 of Ch. VII]. He gave extensive tables, and references to papers on
higher residues and to tables relating to period lengths.

O. Fujimaki^^* noted that if 10'" — 1 is exactly divisible by n, and the
quotient is Qi. . .a^ of jn digits, the numbers obtained from the latter by
cycHc permutations of the digits are all multiples of Ci . . . a^.

J. Cullen, D. Biddle, and A. Cunningham^ ^^ proved that the large factor
of 14 digits of (10-^+l)/(10Hl) is a prime.

L. Kronecker^^^ treated periodic fractions to any base.

W. P. Workman^^^ corrected three errors in Shanks'^^ table.

D. Biddle^^^ concluded erroneously that (10^^ — 1)/9 is a prime.

H. Hertzer"' extended Kessler's^"'^ table from 100000 to 112400, noted
Reuschle's'*'^ error on the conditions that 10 be a biquadratic residue of a
prime p and gave the conditions that 10 be a residue of an 8th power
modulo p. For errata in the table, see Cunningham. ^^

P. Bachmann^'° proved the chief results on periodic fractions and cyclic
numbers to any base g.

A. Tagiuri^^^ proved theorems [F. Meyer ,^ Perkins^^] on purely periodic
fractions to any base and on mixed fractions.

E. B. Escott^^^ noted a misprint in Bickmore's^^^ table and two omissions
in Lucas'^^ table, but described inaccurately the latter table, as noted by
A. Cunningham. ^^^

A. Cunningham^^^ described various tables (cited above) which give
the exponent to which 10 belongs, and listed many errata.

J. R. Akerlund^^° gave the prime factors of 11 ... 1 (to n digits) for n^ 16,
n = 18.

K. P. Nordlund^^^ applied to periodic fractions the theorem that, if
Til, . . ., rir are distinct odd primes, no one dividing a, then N = ni"''. . . Ur""^
di\'ides a^ — l, where A: = 0(iV)/2'""\ He gave the period of \/p for p a
prime < 100 and of certain a/p.

T. H. Miller, ^-^ generalizing the fact that the successive pairs of digits
in the period for 1/7 are 14, 28, ... , investigated numbers n to the base r
for which

1 _2n 4n 8n

~ — 2"~1 4 I 6 ~r • • • )

n r r r"

»"Jour. of the Physics School in Tokio, 7, 1897, 16-21; Abh. Gesch. Math. Wiss., 28, 1910, 22.

i"Math. Quest. Educat. Times, 72, 1900, 99-101.

"'Vorlesungen iiber Zahlentheorie, I, 1901, 428-437.

"'Messenger Math., 31, 1901-2, 115.

"«7&id., p. 34; corrected, ibid., 33, 1903^, 126 (p. 95).

"•Archiv Math. Phys., (3), 2, 1902, 249-252.

""Niedere Zahlentheorie, I, 1902, 351-363.

"iPeriodico di Mat., 18, 1903, 43-58.

»«Xouv. Ann. Math., (4), 3, 1903, 136; Messenger Math., 33, 1903-4, 49.

'"Messenger Math., 33, 1903-4, 95-96.

^^Ibid., 14.5-155.

'"Nj-t Tidsskrift for Mat., Kjobenhavn, 16 A, 1905, 97-103.

'"Goteborgs Kungl. Vetenskaps-Handlingar, (4), VII-VIII, 1905.

"'Proc. Edinburgh Math. Soc, 26, 1907-8, 95-6.

Chap. VI] PERIODIC DECIMAL FRACTIONS. 177

whence r^ — 2n^ = 2. Besides the case r = 10, n = 7, he found r = 58, n = 41 ,
etc.

A. Cunningham^^* noted two errors in his paper"^ and added
252^2 = ^j^o^ 9972>)^ 390112^ = 1 (mod 17«)

and cases modulo p^, where p = 103, 487, attributed to Th. Gosset.

A. Cunningham^^^ gave tables of the periods of \/N to the bases 2, 3, 5
for N^ 100.

H. Hertzer^^" noted three errors in Bickmore's^°* table.

A. Gerardin^^^ gave factors of 10" — 1, n<100, and a table of the expo-
nents to which 10 belongs modulo p, a prime < 10000, with a list of errors
in the tables by Burckhardt and Desmarest.

A. Filippov^^^ gave two methods of determining the generating factor
for the periodic fraction for 1/6 (cf. Lucas, Th^orie des nombres, p. 178).

G. C. Cicioni^^^ treated the subject.

E. R. Bennett^^^ proved the standard theorems by means of group
theory.

W. H. Jackson^^^ noted that, if a is prime to 10 and if h is chosen so that
h< 10, a& = 10m — 1, the period for \/a may be written as

6]l + 10m+(10m)2+. . .+(10m)'-it -A;-10',

where s is the exponent to which 10 belongs modulo a, and /c is a positive
integer. Thus for a = 39, 6 = 1, we have m = 4, s = 6, and the period is

1+40+. . . + (40)^-A:-10^ ^ = .025641.

G. Mignosi^^^ discussed the logic underlying the identification of an
unending decimal with its generator y/q.

A. Cunningham^^^ treated periodic decimals with multiples having the
same digits permuted cyclically.

F. Schuh^^^ considered the length g^ of the period for 1/p" for the base g,
where p is a prime. He proved that qa is of the form qip% where 0^ c^ a — 2
when p = 2, a>2, while O^c^a — 1 in all other cases. For a>2,

?a-l = giP""\ • • • , qa-c+1 = qiVj Qa-c = • • • = ?2 = ?,

where q = qi txcept when p = 2, gr = 4m — 1, and then g = 2. Equality of
periods for moduli p" and p'' can occur for an odd prime p only when this
period is gi, and for p = 2 only when it is 1 or 2. It is shown how to find
the numbers g which give equal periods for p" and p, and the odd numbers
g which give the period 2 for 2".

"8Math. Gazette, 4, 1907-8, 209-210. Sphinx-Oedipe, 8, 1913, 131.

"9Math. Gazette, 4, 1907-8, 259-267; 6, 1911-12, 63-7, 108-116.

"OArchiv Math. Phys., (3), 13, 1908, 107.

"^Sphinx-Oedipe, Nancy, 1908-9, 101-112.

"'Spaczinskis Bote, 1908, pp. 252-263, 321-2 (Russian).

"'La divisibiht^ dei numeri e la teoria delle decimaU periodiche, Perugia, 1908, 150 pp.

"«Amer. Math. Monthly, 16, 1909, 79-82.

"'Annals of Math., (2), 11, 1909-10, 166-8.

"'II Boll. Matematica Gior. Sc.-Didat., 9, 1910, 128-138.

"^Math. Quest. Educat. Times, (2), 18, 1910, 25-26.

"'Nieuw Archief Wiskunde, (2), 9, 1911, 408-439. Cf. Schuh,"'"*, Ch. VII.

178 History of the Theory of Numbers. [Chap, vi

T. Ghezzi^^^ considered a proper irreducible fraction m/p with p prime
to the base b of numeration. Let h belong to the exponent n modulo p. In

7nb = pqi-\-ri, rih = pq2+r2,. . ., 0<ri<p, 0<r2<p,. . .,

fi,. . ., r„ are distinct and r„ = w. Multiply the respective equations by
6""^, 6""^,. . . and add; we see that

p hr-i

A similar proof shows that m/p equals a fraction ^xith. the denominator
b'{b'* — l) when 6 = aia2a3, p^piCL^a^a^^ the a's being primes and pi rela-
tively prime to b, while 6' is the least power of b having the di\isor ai^a^a^,
and n is the exponent to which b belongs modulo pi.

F. Stasi^*° gave a long proof showing that the length of the period for
b/a does not exceed that for 1/a. If the period A for 1/p has m digits and
n = p5 is prime to 10, the length of the period for \/n is m if A is divisible
by q; is mi if A is prune to q and if the least A(10'"^*"^^+ . . . +1) divisible
by q has m = i; and is mj if A=A'a, q = aq', with A', q' relatively prime,
while the least A' (10"'^*'-^^+ ... +1) divisible by q' has k=j. For a prime
p5^2, 5, let

1 A

h

i

p'' 10"* -1'

and let A^ be the first of the periods of successive powers of 1/p not divisible
by p; then the period for l/p''+^' has wp^' digits. If p, is a prime 9^2, 5,
and Ti is the length of the period for l/p„ and if l/pj^< is the highest power
of 1/pi with a period of Ti digits, the length of the period for l/p,"* is
T-' = r{pi''i~^i and that for l/II Pi"< is a multiple of the 1. c. m. of the r/.

If n is prime to 10 and if ri, . . . , r;„ = 1 are the successive remainders on
reducing \/n to a decimal, then r^=r2i (mod n). Hence if 1/n has a period
of 2i digits, r^ = \ (mod n) and conversely. But if it has a period of
2i+l digits, r-+i = 10 and conversely.

*K. W. Lichtenecker^^^ gave the length of the period for 1/p, when p is
a prime ^307, and the factors of 10^ — 1, r?^ 10.

L. Pasternak^^^ noted that, after multiplying the terms of a fraction by
9, 3 or 7, we may assume the denominator iV' = 10m — 1. To convert Rq/N
into a decimal, we have 10Rk-i = Nyk+Rk (^ = 1, 2, . . .). Set 7?^. = lOz^+e^t,
ek^ 9. Since Vk'^ 9, e^ = Vk and Rk-i = mCk+Zk. Hence the successive digits
of the period are the unit digits of the successive remainders.

E. Maillet^^^ defined a unique development Oo+ai/n+ 02/11^+ ... of an
arbitrary number, where the Oi are integers satisfjdng certain conditions.
He studied the conditions that the development be limited or periodic.

"»I1 Boll. Matematica Gior. Sc.-Didat., 9, 1910, 263-9.
""/bid., 11, 1912, 226-246.

i"Zeit3chr. fur das Realschulwesen, 37, 1912, 338-349.
i^L'enseignement math., 14, 1912, 285-9.
»"L'interm6diaire des math., 20, 1913, 202-6.

Chap. VI] PERIODIC DECIMAL FRACTIONS. 179

Welsch^** discussed briefly the length of the period of a decimal fraction.

B. Howarth^^^ noted that D^ is not a factor of (10^"-1)/(10'*-1) if D is
a prime and n is not a multiple of the length of the period for 1/D. Again/^^
(^IQmnp^- _i)/9 is not divisible by (lO'"^-!) (10"^-1)/81.

A. Cunningham^^^ factored 10^^ ± 1. Known factors of lO"^ 1 are given.

Cunningham^^^ gave factors of 10"*^'* — !.

A. Leman^^^ gave an elementary exposition and inserted proofs of Fer-
mat's theorem and related facts, with the aim to afford a concrete introduc-
tion to the more elementary facts of the theory of numbers.

S. Weixer^^'' would compute the period P for 1/p by multiplication,
beginning at the right. Let c be the final digit of P, whence pc = 10z — l.
Then c is the first digit of the period P^ for z/p. The units digit Ci of
cz = 10zi-\-Ci is the tens digit of P and the units digit of P^. In CiZ-\-Zi =
1022+^2, C2 is the hundreds digit of P and the tens digit of P\ etc.

A. Leman^^^ discussed the preceding paper.

Problems^^^ on decimal fractions may be cited here.

O. Hoppe^^^ proved that (10^^ — 1)/9 is a prime.

M. Jenkins^^^ noted that if iV= a^6^. . . , where a,h,. . .are distinct primes
9^2, 5, the period for 1/N is complementary (sum of corresponding digits of
the half periods is 9) if and only if the lengths of the periods for 1/a, 1/b,. . .
contain the same power of 2.

Kraitchik^^^ of Ch. VII and Levanen^^ of Ch. XII gave tables of ex-
ponents to which 10 belongs. Bickmore and Cullen^^^ of Ch. XIV factored
10^^+1.

Further Papers Involving No Theory of Numbers.

J. L. Lagrange, Legons 61em. k I'^cole normale en 1795, Oeuvres 7, 200.
James Adams, Annals Phil., Mag. Chem. (Thompson), (2), 2, 1821, 16-18.

C. R. Telosius and S. Morck, Disquisitio. . . . Acad. Carolina, Lundae,
1838 (in Meditationum Math. . . . PubHce Defendant C. J. D. Hill, 1831,
Pt. II).

J. A. Arndt, Archiv Math. Phys., 1, 1841, 101-4.

J. Dienger, ibid., 11, 1848, 232; Jour, fur Math., 39, 1850, 67.

Wm. Wiley, Math. Magazine, 1, 1882, 7-8.

A. V. Filippov, Kagans Bote, 1910, 214-221 (pedagogic).

i*^L'intermediaire des math., 21, 1914, 10.

"sMath. Quest. Educat. Times, 28, 1915, 101-4.

"»76id., 27, 1915, 33-4.

^"Ibid., 29, 1916, 76, 88-9.

i"Math. Quest, and Solutions, 3, 1917, 59.

"'Vom Periodischen Dezimalbruch zur Zahlentheorie, Leipzig, 1916, 59 pp.

""Zeitschrift Math. Naturw. Unterricht, 47, 1916, 228-230.

i"/6id., 230-1.

i"Zeitschrift Math. Naturw. Unterricht, 12, 1881, 431; 20, 188; 23, 584.

i^Proc. London Math. Soc, Records of Meeting, Dec. 6, 1917, and Feb. 14, 1918, for a revised

proof.
i"Math. Quest. Educ. Times, 7, 1867, 31-2. Minor results, 32, 1880, 69; 34, 1881, 97-8: 37,

1882, 44; 41, 1884, 113-4; 58, 1893, 108-9; 60, 1894, 128; 63, 1895, 34; 72, 1900, 75-6;

74, 1901, 35; (2), 2, 1902, 65-6, 84-5; 4, 1903, 29, 65-7, 95; 7, 1905, 97, 106, 109-10; 8,

1905, 57; 9, 1906, 73. Math. Quest, and Solutions, 3, 1917, 72 (table); 4, 1917, 22.

I

4

I

CHAPTER VII.

PRIMITIVE ROOTS. BINOMIAL CONGRUENCES.
Primitive Roots, Exponents, Indices.

J. H. Lambert^ stated without proof that there exists a primitive root
g of any given prime p, so that g^ — \ is divisible by p for e = p — 1, but not
for 0<e<p — 1.

L. Euler^ gave a proof which is defective. He introduced the term
primitive root and proved (art. 28) that at most n integers a;<p make
x" — 1 divisible by p, the proof applying equally well to any polynomial
of degree n with integral coefficients. He stated (art. 29) that, for n<p,
x" — 1 has all n solutions "real" if and only if n is a divisor of p — 1; in par-
ticular, x^~^ — l has p — 1 solutions (referring to arts. 22, 23, where he
repeated his earlier proof of Fermat's theorem). Very likely Euler had
in mind the algebraic identity a;^"^ — l = (x" — 1)Q, from which he was in a
position to conclude that Q has at most n— p+1 solutions, and hence x" — 1
exactly n. By an incomplete induction (arts. 32-34), he inferred that there
are exactly </)(n) integers x<p for which x" — 1 is divisible by p, but x^ — \
not divisible by p for 0<Z<n, n being a divisor of p — 1 (as the context
indicates). In particular, there exist <f>{p — l) primitive roots of p (art. 46).
He listed all the primitive roots of each prime ^ 37.

J. L. Lagrange^ proved that, if p is an odd prime and

a:P-i-l=Z^+pF,
where X, ^, F are polynomials in x with integral coefficients, and if x"" and x"
are the highest powers of a; in X and ^ with coefficients not divisible by p,
there are m integral values, numerically <p/2, of x which make X a mul-
tiple of p, and fi values making ^ a multiple of p. For, by Fermat's theorem,
the left member is a multiple of p for a; = ± 1, ± 2, . . . , =*= (p — 1)/2, while at
most m of these values make X a multiple of p and at most fx make ^ a
multiple of p.

L. Euler^ stated that he knew no rule for finding a primitive root and
gave a table of all the primitive roots of each prime ^41.

Euler^ investigated the least exponent x (when it exists) for which
fa'+g is divisible by N. Find X such that —g^\N is a multiple, say aV,
of a. Then fa'-^-r is divisible by N. Set r=FX'iV = a^s, ^^1. Then
j'gx-a-ff_^ is divisible by N; etc. If the problem is possible, we finally get
/ as the residue of /a"^""" • • • "^, whence x = a+. . . +f . For example, to find
the least x for which 2"" — 1 is divisible by iV = 23, we have

1+23 = 2^3, 3-23= -2^5, -5-23= -2^7, -7-^23 = 2^,
whence a^ = 3+2+2+4 = ll.

^Nova Acta Eruditomm, Leipzig, 1769, p. 127.
''Novi Comm. Acad. Petrop., 18, 1773, 85; Comm. Arith., 1, 516-537.
^Nouv. M6m. Ac. Roy. Berlin, ann^e 1775 (1777), p. 339; Oeuvres 3, 777.
<0pu8c. Anal., 1, 1783 (1772),. 121; Comm. Arith., 1, 506.

^Opusc. Anal., 1, 1783 (1773), 242; Comm. .\i-ith., 2, p. 1; Opera postuma, I, 172-4.

181

r

182 History of the Theory of Numbers. [Chap, vii

A. M. Legendre^ started with Lagrange's' result that, if p is a prime
and n is a divisor of p — 1,
(1) a:" = l(modp)

has n incongruent integral roots. Let n = v^v'^ . . ., where v, v',. . . are dis-
tinct primes. A root a of (1) belongs* to the exponent n if no one of
a"/', a"^', . . . is congruent to unity modulo p. For, if a* = l, 0<d<n, let
a be the g. c. d. of 6, n, so that a = ny—dz for integers y, z; then

contrary to hypothesis. Next, of the n roots of (1), n/v satisfy x''^'' = l
(mod p), and n{l — l/v) do not. Likewise, n{l — l/v') do not satisfy
2.n/«'' = 1 . qIq i^ jg gaj(j ^Q follow that there are

*(„)=„ (i-i)(i-i)

numbers belonging to the exponent n modulo p. If
^•^^1, ^-^-^Kmodp),

/3 belongs to the exponent v"". If j8' belongs to the exponent v'^, etc., the
product /3]S' ... is stated to belong to the exponent n.

C. F. Gauss^ gave two proofs of the existence of primitive roots of a
prime p. If d is a divisor of p — 1, and a'' is the lowest power of a congruent
to unity modulo p, a is said to belong to the exponent d modulo p. Let
ypid) of the integers 1, 2, . . . , p — 1 belong to the exponent d, a given divisor
of p — 1 . Gauss showed that i/' (c?) = 0 or 0 (d) , 2 1/' (c^) = p — 1 = 2 <^ (d) , whence
i^(d) —(t>{d). In his second proof, Gauss set p — 1 =a"6'^. . ., where a, 5, . . .
are distinct primes, proved the existence of numbers A, B,. . . belonging
to the respective exponents a", h^,. . ., and showed that AB . . . belongs to
the exponent p — 1 and hence is a primitive root of p.

Let a be a primitive root of p, h any integer not divisible by p, and e
the integer, uniquely determined modulo p — 1, for w^hich o* = 6 (mod p).
Gauss (arts. 57-59) called e the index of h for the modulus p relative to the
base a, and wrote e = ind h. Thus

a'^^^'^b (mod p), ind 66'=ind 6+ind h' (mod p-1).

Gauss (arts. 69-72) discussed the relations between indices for different
bases and the choice of the most convenient base.

In articles 73-74, he gave a convenient tentative method for finding a
primitive root of p. Form the period of 2 (the distinct least positive resi-
dues of the successive powers of 2); if 2 belongs to an exponent ^<p — 1,
select a number 6<p not in the period of 2, and form the period of 6; etc.

If a belongs to the exponent t modulo p, the product of the terms in the
period of a is = ( — 1)'+^ (mod p), while the sum of the terms is =0 unless
a=l (arts. 75, 79).

•M6m. Ac. R. Sc, Paris, 1785, 471-3. Thdorie des nombres, 1798, 413-4; ed. 3, 1830,

Nos. 341-2; German transl. by Maser, 2, pp. 17-18.
*This term was introduced later by Gauss.''
^Disquisitiones Arith., 1801, arts. 52-55.

Chap. VII] PRIMITIVE RoOTS, EXPONENTS, INDICES. 183

The product of all the primitive roots of a prime p^3 is =1 (mod p) ;
the sum of the primitive roots of p is =0 if p — 1 is divisible by a square,
but is =( — 1)" if p — 1 is the product of n distinct primes (arts. 80, 81).

If p is an odd prime and e is the g. c. d. of ^(p")=p''~^(p — 1) and t,
then x' = l (mod p") has exactly e incongruent roots. It follows that there
exist primitive roots of p", i. e., numbers belonging to the exponent 0(p")
(arts. 85-89).

For n>2, every odd number belongs modulo 2" to an exponent which
divides 2""^, so that primitive roots of 2" are lacking; however, a modified
method of employing indices to the base 5 may be used (arts. 90, 91).

If w = A"5^.., where A, B,... are distinct primes, and a=0(A"),
^=4>{B^), . . ., and if ii is the 1. c. m. of a, jS, . . ., then ^'' = 1 (mod m) for z
prime to m. Now fiKa-^. . . =4>{m) except when m = 2", p" or 2p", where
p is an odd prime. Thus there exist primitive roots of m only when m = 2,
4, p"or2p" (art. 92).

Table I, at the end of Disq. Arith., gives on one page the indices of each
prime <p for each prime and power of prime modulus < 100. Gauss gave
no direct table to determine the number corresponding to a given index,
but indicated (end of art. 316) how his Table III for the conversion of ordi-
nary into decimal fractions leads to the number having a given index (cf.
Gauss,i^'i^Ch. VI).

S. F. Lacroix^ reproduced Gauss' second proof of the existence of primi-
tive roots of a prune, without a reference.

L. Poinsot^ argued that the primitive roots of a prime p may be obtained
from the algebraic expressions for the imaginary (p — l)th roots of unity
by increasing the numbers under the radical signs by such multiples of p
that the radicals become integral. The (/)(p — 1) primitive roots of p may
be obtained by excluding from 1, . . . , p — 1 the residues of the powers whose
exponents are the distinct prime factors of p — 1; while symmetrical, this
method is unpractical for large p.

Fregier^° proved that the 2"th power of any odd number has the remainder
unity when divided by 2""*"^, if n>0.

Poinsot^^ developed the first point of his preceding paper. The equa-
tion for the primitive 18th roots of unity is x^—x^-\-l=0. The roots are

: = a^^Kl + ^^'=^ (a' = l).

But \/^= ±4, -¥^=4:, ^-11 = 2 (mod 19). Thus the six primitive
roots of 19 are x= —4, 2, —9, —5, —6, 3. In general, the algebraic expres-
sions for the nth roots of unity represent the different integral roots of
a;" = l (mod p), where p is a prime kn-\-\, after suitable integers are added
to the numbers under the radical signs. Since unity is the only (integral)

sCompldment des ^l^mens d'alg^bre, Paris, ed. 3, 1804, 303-7; ed. 4, 1817, 317-321.

«M6m. Sc. Math, et Phys. de I'Institut de France, 14, 1813-5, 381-392.
"Annales de Math, (ed., Gergonne), 9, 1818-9, 285-8.
"M6m. Ac. Sc. de I'Institut de France, 4, 1819-20, 99-183.

184 History of the Theory op Numbers. [Chap, vii

root of x^=l (mod p), if p is a prime >2, he concluded (p. 165) that p is
a factor of the numbers under the radical signs in the formula for a primitive
pth root of unity. Cf. Smith^^^ of Ch. VIII.

Poinsot^^" again treated the same subject.

J. Ivory^^ stated that a primitive root of a prime p satisfies x^^~^^^^^ — 1,
but no one of the congruences x'=—l (mod p), <=(p — l)/(2a), where a
ranges over the odd prime factors of p — 1 ; while a number not a primitive
root satisfies at least one of the a;' = — 1 . Hence if each a' ^ — 1 and
^(p-i)/2^ — 1, then a is a primitive root.

V. A. Lebesgue^^ stated that prior to 1829 he had given in the Bulletin
du Nord, Moscow, the congruence X = 0 of Cauchy^^ for the integers
belonging to the exponent n modulo p.

A. Cauchy^^ proved the existence of primitive roots of a prime p, essen-
tially as in Gauss' second proof. If p — 1 is divisible by n = a"6V . . . , where
a, b, c,. . . are distinct primes, he proved that the integers belonging to the
exponent n modulo p coincide with the roots of

Y (a^"-l)(a:"^°^-l)(a;"/°--l)... _^ , , ,
^=(x"/"-l)(a:''/^-l)...(a:"/-^-l)...=^ ^^^^ P^'

The roots of the equation X = 0 are the primitive nth roots of unity. For
the above divisor n of p — 1, the sum of the Zth powers of the primitive
roots of a;" = 1 (mod p) is divisible by p if Z is divisible by no one of the
numbers

n, n/a, n/h, . . . , n/ab, . . . , n/ahc, ....

But if several of these are divisors of I, and if we replace n, a, b,. . . by
<t>{n), 1—a, 1 — 6, . . . in the largest of these divisors in fractional form, we
get a fraction congruent to the sum of the Ith. powers. In case x'" = l
(mod p) has m distinct integral roots, the sum of the lib. powers of all the
roots is congruent modulo p to m or 0, according as I is or is not a multiple
of m.

M. A. Stern^^ proved that the product of all the numbers belonging to
an exponent d is = 1 (mod p) , while their sum is divisible by p if d is divisible
by a square, but is = ( — 1)" if d is a product of n distinct primes (generaliza-
tions of Gauss, D. A., arts. 80, 81). If p = 2n+l and a belongs to the expo-
nent n, the product of two numbers, which do not occur in the period of a,
occurs in the period of a. To find a primitive root of p when p — 1 = 2ab . . . ,
where a,b,. . . are distinct odd primes, raise any number as 2 to the powers
(p — l)/a, (p — 1)/6, . . . ; if no one of the residues modulo p is 1, the negative
of the product of these residues is a primitive root of p; in case one of the
residues is 1, use 3 or 5 in place of 2. If p = 2g+l and q are odd primes, 2
or — 2 is a primitive root of p according as p = 8n + 3 or 8n + 7 . If p = 4^^ -f-1

"''Jour, de I'dcole polytechnique, cah. 18, t. 11, 1820, 345-410.
"Supplement to Encyclopaedia Britannica, 4, 1824, 698.
"Jour, de Math., 2, 1837, 258.

"Exercices de Math., 1829, 231; Oeuvrea, (2), 9, 266, 278-90.
"Jour, fiir Math., 6, 1830, 147-153.

Chap. VII] PRIMITIVE RoOTS, EXPONENTS, INDICES. 185

and q are primes, 2 and —2 are primitive roots of p. If p = 4g+l and
g = 3n+l are primes, 3 and —3 are primitive roots of p.

F. Minding^^ gave without reference Gauss' second proof of the exist-
ence of primitive roots of a prime.

F. J. Richelot^^ proved that, if p = 2"'+l is a prime, every quadratic
non-residue (in particular, 3) is a primitive root of p.

A. L. Crelle^^ gave a table showing all prime numbers ^ 101 having a
given primitive root; also a table of the residues of the powers of the
natural numbers when divided by the primes 3, . . ., 101. His device^^
for finding the residues modulo p of the powers of a will be clear from the
example p = 7, a = 3. Write under the natural numbers <7 the residues
of the successive multiples of 3 formed by successive additions of 3 ; we get

12 3 4 5 6
3 6 2 5 14.

Then the residues 3, 2, 6, . . . of 3, 3^, 3^, . . . modulo 7 are found as follows:
after 3 comes the number 2 below 3 in the above table; after 2 comes the
number 6 below 2 in the table; etc.

Crelle^° proved that, if p is a prime and X is prime to p — 1 and <p — 1,
the residues modulo p of z^ range with z over the integers 1, 2,. . ., p — 1.
His proof that there exist (^(n) numbers belonging to the exponent n
modulo p, if n divides p — 1, is like that by Legendre.^

G. L. Dirichlet^^ employed 0(A:) systems of indices for a modulus
/j = 2^p'p"'. . ., where p, p', . . . are distinct primes, and X^3. Given any
integer n prime to k, and primitive roots c, c', . • • of P'> v" \ • • • > we can
determine indices a, /3, 7, 7', . . . such that

n=(-l)''5^ (mod 2^^), n = c^ (mod p'), n = c"'' (mod p"'),- • ••

Michel Ostrogradsky^^ gave for each prime p<200 all the primitive
roots of p and companion tables of the indices and corresponding numbers.
(See Jacobins and Tchebychef .3^)

C. G. J. Jacobi^^ gave for each prime and power of a prime < 1000 two
companion tables showing the numbers with given indices and the index
of each given number. In the introduction, he reproduced the table by
Burckhardt, 1817, of the length of the period of the decimal fraction for
1/p, for each prime p^2543, and 22 higher primes. Of the 365 primes
<2500, we therefore have 148 having 10 as a primitive root, and 73 of the
form 4w+3 having —10 as a primitive root. Use is made also of the
primes for which 10 or — 10 is the square or cube of a primitive root.

"Anfangsgrlinde der hoheren Arith., 1832, 36-37.

"Jour, ftir Math., 9, 1832, p. 5.

^Hhid., 27-53.

"Also, ihid., 28, 1844, 166.

"Abh. Ak. Wiss. BerUn, 1832, Math., p. 57, p. 65.

^HhU., 1837, Math., 45; Werke, 1, 1889, 333.

"Lectures on alg. and transc. analysis, I-II, St. P^tersbourg, 1837; M6m. Ac. Sc. St. P6tera-

bourg, s6r. 6, sc. math, et phys., 1, 1838, 359-85.
2'Canon Arithmeticus, Berlin, 1839, xl+248 pp. Errata, Cunningham.""-""

186

History of the Theory of Numbers.

[Chap. VII

To find a primitive root g of p, select any convenient integer a and form
the residues of a, or, a^,. . . [as by Crelle^®]. Let n be the exponent to
which a belongs. Set nn' = p — \. If n<p — 1, select an integer h not in
the period a, . . . , a". The residue of 6" is in this period of a. If y is the
least power of 6 whose residue is in the period of a, then / divides n', say
w'=i/' (P- xxiii). Since a=g'^', h^=a\ we have

y^gf^''^g"''^''"'\ h = g^'^'+'^^ (mod p),

for some value 0, 1, . . . , /—I of k. But A: must be chosen so that i+nk is
prime to /. For, if i-\-nk = du, where d is a divisor of /, we would have
5^'' = a". The nf residues of a'b' (r = 0,. . ., n-1; s = 0,. . ., /-I) are dis-
tinct ; their indices to base g are/', 2f', . . . , nff in some order and are known.
If nf'<p — l, we employ an integer not in the set a^b' and proceed similarly.
Ultimately we obtain a primitive root and at the same time the index of
everj" number. This method was used for the primes between 200 and 1000.

For primes < 200, the tables by Ostrogradsky^^ w^ere reprinted with the
same errors (noted at the end of the Canon).

Jacobi proved that, if n is an odd prime, any primitive root of n^ is a
primitive root of any higher power of n (p. xxxv).

For the modulus 2", 4^iu^9, the final tables give the index / of any
positive odd number to base 3, where

(_l)(Ar-l)W-3)/8^ = 37 (jjjQ^ 2").

Robert ]\Iurphy-^ stated the empirical theorem that every prime
anr+p has a as a primitive root if p>a/2, p is a prime <a, and if a is a
primitive root of p. For example, a prime 10nr-{-7 has 10 as a primitive
root.

H. G. Erlerus'^ considered two odd primes p and p' and a number m
such that m=a (mod p), m = a' (mod p'). Let a belong to the exponent
e modulo p, and a' to the exponent e' modulo p\ If 8 is the g. c. d. of
e and e', then m belongs to the exponent ee'/8 modulo pp'. He discussed
at length the number of integers belonging to the exponent n for a com-
posite modulus.

A. Cauchy^^ called the least positive integer i for which m' = 1 (mod n)
the indicator relative (or corresponding) to the base m and modulus n,
which are assumed relatively prime. If the base m is constant, and ii, 12
are the indicators corresponding to moduli nj, 112, and if n = nin2 is prime
to 772, then the 1. c. m. of I'l and {2 is the indicator corresponding to modulus
n. If the modulus n is constant, and ii, io are the indicators corresponding
to bases Wi, ^2, and if I'l, 1*2 are relatively prime, then 1*112 is the indicator
corresponding to the base 7^17^2.

Let I'l, io be the indicators corresponding to the bases mi, 7722 and same
modulus n. The g. c. d. 0; of I'l, 2*2 can be expressed (often in several ways)
as a product uv such that ii/u, io/v are relatively prime. For, if co = a/3. . . ,

"Phil. Mag., (3), 19, 1841, 369.

"Elementa Doctrinse Numerorum, Diss., Halis, 1841, 18-43.

»«Comptes Rendus Paris, 12, 1841, 824-845; Oeuvres, (1), 6, 124-146.

Chap. VII] PRIMITIVE RoOTS, EXPONENTS, INDICES. 187

where a, j8, . . . are powers of distinct primes, use a as a factor in forming u
in case a is prime to ii/a, but as a factor of y in case a is prime to zVa, and
as a factor of either u or v indifferently in case a is prime to both ii/a and
12/0. Since ii/u and i2/v are relatively prime indicators corresponding to
bases mi" and m2^ it follows from the preceding theorem that the indicator
corresponding to base mi"-W2'' and modulus n is

ii ^2 iii2 1 r • •
= — = 1. c. m. of ii, i2.

U V £0

Hence, given several bases mi, m2, . . . and a single modulus n, we can
find a new base relative to which the indicator is the 1. c. m. of the indicators
corresponding to mi, m2, .... If the latter bases include all the integers <n
and prime to n, the corresponding indicators give all indicators which can
correspond to modulus n, so that all of them divide a certain maximum
indicator I. Then for every integer m relatively prime to n,m^ = l (mod n) .
If n = v°', where v is an odd prime, or if n = 2 or 4, l=^{n). If n = 2^ k>2,
I=(f}{n)/2. If Ij is the maximum indicator corresponding to a power Uj
of a prime, and if n = llnj, then I is the 1. c. m. of /i, /2, • • •• The equation
mx — ny = l has the solution x = 7n^~^ (mod n).

Cauchy^^ republished the preceding paper, but with an extension from the
limit n = 100 to the limit n = 1000 for his table of the maximum indicator I.

C. F. Arndt^^ gave (without reference) Gauss' second proof of the exist-
ence of a primitive root of an odd prime p, and proved the existence of the
<^(p") primitive roots of p'* or 2p'', and that there are no primitive roots for
moduli other than these and 4. If i is a divisor of 2""^, n>2, exactly t
numbers belong to the exponent t modulo 2'' (p. 18). If, for a modulus
p", 2p", a belongs to the exponent t, then a-a^ . . .a' is congruent to ( — 1)'+^
(pp. 26-27), while the product of the numbers belonging to the exponent t
is congruent to +1 if ^?^ 2 (pp. 37-38). He proved also Stern's^^ theorem
on the sum of these numbers. He gave the same two theorems also in a
later paper. ^^

L. Poinsot^" used the method of Legendre^ to prove the existence of
4>{n) integers belonging to the exponent n, sl divisor of p — 1, where p is a
prime. He gave (pp. 71-75) essentially Gauss' first proof, and gave his
own^ method of finding primitive roots of a prime. The existence of
primitive roots of p", 2p", 4, but of no further moduli, is established by use
of the number of roots of binomial congruences (pp. 87-101).

C. F. Arndt^^ noted that if a belongs to an even exponent t modulo 2",
then ±a, ±a^, ..., ±a'~^ give the t incongruent numbers belonging to
the exponent t, and are congruent to A; • 2"" =f 1 (A; = 1 , 3, 5, . . . ) . The product
of the numbers belonging to the exponent t modulo 2", n>2, is = +1.

• "Exercices d' Analyse et de Phys. Math., 2, 1841, 1-40; Oeuvres, (2), 12.
"Archiv Math. Phys., 2, 1842, 9, 15-16.
"Jour, flir Math., 31, 1846, 326-8.
3«Jour. de Math^matiques, (1), 10, 1845, 65-70, 72.
"Archiv Math. Phys., 6, 1845, 395, 399.

188

History of the Theory of Numbers.

[Chap. VII

E. Prouhet^" gave, without reference, Crelle's^' method of forming the
residues of the powers of a number. The object of the paper is to give a
uniform method of proof of theorems, given in various places in Legendre's
text, relating to the residues of the first n powers of an integer belonging
to the exponent n modulo P, especially when P is a prime or a power of a
prime, and the existence of primitive roots. He gave (p. 658) the usual
proof that =•= 2 is a primitive root of a prime 2^+ 1 if 5 is a prime 4/c± 1 (with
a misprint).

C. F. Arndt^^ proved that if ^ is a primitive root of the odd prime p and
if p^ (SKn) is the highest power of p dividing G = g^~^ — 1, then g belongs
to the exponent p'*~''(p — 1) modulo p". Conversely, if the last is true of a
primitive root g of p, then G is divisible by p^ and not by p^"'"^ The first
result with X = 1 shows that any primitive root of p^ is a primitive root of
p", n>2. Let g he a, primitive root of p; if G is not divisible by p^, g is a.
primitive root of p^; but if G is divisible by p^, and h is not divisible by p,
then g+hp is a primitive root of p^. Any odd primitive root of p** is a
primitive root of 2p". If gr is a primitive root of p'* or 2p'*, and t is a divisor
of p"~^(p — 1), then if a ranges over the integers <t and prime to t, the
<f>{t) integers belonging to the exponent t modulo p" or 2p" are g% where
e = p"~^(p — l)a/<. The numbers belonging to the exponent 2"""* modulo
2" are found more simply than by Gauss'^ and Jacobi^^ (p. 37).

P. L. Tchebychef^^ proved that if a, /3, . . . are the distinct prime factors
of p — 1, where p is a prime, then a is a primitive root of p if and only if no
one of the congruences x'' = a, xP = a,. . . (mod p) has an integral root.
This furnishes a method (usually impracticable) of finding all primitive
roots of p. A second method uses a number a belonging to the exponent n,
and a number h not congruent to a power of a, and deduces a number
belonging to an exponent >n. In the second supplement, he proved that
3 is a primitive root of any prime 2^"+ 1 ; that =*= 2 is a primitive root of any
prime 2a +1 such that a is a prime 4A:± 1 ; 3 is a primitive root of 4iV2"'4-l
if w>0 and iV is a prime >9^ /(4-2'"); 2 is a primitive root of any prime
4iVH-l such that A^ is an odd prune. The last result was later proposed'^
as a question for solution (with reference to this text) . There is given the
table of primitive roots and indices for primes < 200, due to Ostrogradsky^^.
Schapira (p. 314) noted that in the list of errata in Jacobi's^^ Canon (p. 222)
there is omitted the error 8 for 6 in ind 14 for p = 25.

V. A. Lebesgue^*^ remarked that Cauchy's^^ congruence X=0 shows
the existence of 0(n) integers belonging to the exponent n modulo p, a
prime.

»«Nouv. Ann. Math., 5, 1846, 175-87, 659-62, 675-83.

»3Jour. fiir Math., 31, 1846, 259-68.

"Theory of Congruences (m Russian), 1849. German translation by Schapira, Berlin, 1889,

p. 192. Italian translation by Mile. Massarini, Rome, 1895, with an extension of the

tables of indices to 353.
»Nouv. Ann. Math., 15, 1856, 353. Solved by use of Euler's criterion by P. H. Rochette,

and., 16, 1857, 159. Also proved by Desmarest,*^ p. 278.
»*Nouv. Ann. Math., 8, 1849, 352; 11, 1852, 420.

Chap. VII] PRIMITIVE RoOTS, EXPONENTS, INDICES. 189

E. Desmarest" devoted the last 86 pages of his book to primitive roots;
the 70 pages claimed to be new might well have been reduced to five by
the omission of trivial matters and the use of standard notations. To find
(pp. 267-8) a primitive root of the prime P = 6g+l, where q is an odd prime,
seek an odd solution of ^^^+3 = 0 (mod P) and set w = 2/2 — 1; then R^=—l
and R belongs to the exponent 6; thus we know the solutions of x^ = l\
let a be any integer prime to P and not such a solution; if a^=±l, then
=ta belongs to the exponent q, and ±ai2 is a primitive root of P; but, if
a^« 7^ 1 , then a^^= =f 1 (mod P) , and =*= a is a primitive root of P. If P = 8Q + 1
and Q are primes, then P=5 (mod 12) and 3 is a quadratic non-residue and
hence a primitive root of P.

Let P be a prime of the form 5q^2. Then u^= 5 (mod P) is not solvable.
Thus, if a is a primitive root of P, 5 = a% where e is odd. Thus if e is prime
to P — 1, 5 is a primitive root of P. It is recommended that 5 be the first
number used in seeking by trial a primitive root. And yet he announced
the theorem (p. 283) that 5 is in general a primitive root. If P is a prime
5g±2 also of the form 2"Q+1, where Q is an odd prime including 1, then
(pp. 284-6) 5 is a primitive root of P provided P is not a factor of 5^ —1.
He gave the factors of the latter and of 10^" — 1 for n = 1, . . . , 5. '

Results, corresponding to those just quoted for 5, are stated for p = 7, — 7,
10, 17. What is really given is a Hst of the linear forms of the primes P
for which p is a quadratic non-residue. If, in addition, P = 2''Q + 1, where
Q is an odd prime, then p is a primitive root, provided p^^^^l (mbd P).
The last condition is ignored in his statement of his results and again in his
collection (pp. 297-8) of "principles which give primitive roots" entered in
his table (pp. 298-300) giving a primitive root of each prime < 10000.

V. A. Lebesgue^^ proved that, if a and p = 2'a+l are primes, any quad-
ratic non-residue x of p is a primitive root of p if

a;2*-'+1^0(modp).

J. P. Kulik^^ gave for each prime p between 103 and 353 the indices and
all the primitive roots of p. His manuscript extended to 1000. There is
an initial table giving the least primitive root of the primes from 103 to 1009.

G. 01tramare^° called x a root of order or index m of a prime piix belongs
to the exponent {p — l)/m modulo p. Let Xm{x) = 0 (mod p) be the con-
gruence whose roots are exclusively the roots of order moi p. By changing
X to x^^"", we obtain Xmn=<l>{^) ^0. li rii, n2, . . . , n are the divisors > 1 of w.

Am — ■

Y Y

'^Th^orie des nombres. Traits de I'analyse ind6terminee du second degr6 k deux inconnues
suivi de I'application de cette analyse k la recherche des racines primitives avec une table
de ces racines pour tous les nombres premiers compris entre 1 et 10000, Paris, 1852,
308 pp. For errata, see Cunningham, Mess. Math., 33, 1903, 145.

58Nouv. Ann. Math., 11, 1852, 422-4.

'9 Jour, fur Math., 45, 1853, 55-81.

"7Wd., 303-9.

190 History of the Theory of Numbers. [Chap, vii

V. A. Lebesgue^^ noted that, given a primitive root g (g<p) of the
prime p, we can find at once the primitive roots of p". Let g' be the positive
residue <p~ when g^ is divided by p^ and set h = {g' — g)/p. Then

g+px+p'^y {y = 0,. . ., p""^-!; x = 0,. . ., p-1; x^h)

give p"~^(p — 1) primitive roots. Replacing g by g\ where i is less than
and prime to p — 1, we obtain 0 ]0(p") } primitive roots of p". In particular,
a primitive root of p~ is a primitive root of p" (Jacobi^). But, if h = 0, g
is not a primitive root of p". Since

ginda+e^p_^ (mod p") , e = ip"-np-l),

we can reduce by half the size of Jacobi's Canon.

D. A. da Silva^^ gave two proofs that x'^ = l (mod p) has (f)(d) primitive
roots, if d divides p — 1, and perfected the method of Poinsot^'^" for finding
the primitive roots of a prime.

F. Landry^^" was led to the same conclusion as Ivory.^^ In particular,
if p = 2* + l, or if p = 2n+l (n an odd prime) and a7^p — l, any quadratic
non-residue a of p is a primitive root. For each prime p< 10000, at least
one prime ^ 19 is a quadratic non-residue of p. Cauchy's^* congruence for
the primitive roots is derived and proved.

G. Oltramare*^ proved that — 3°2^'' is a primitive root of the prime
p = 2a/3 + l, if a^3, /3f^3, S'^^l, 22^^1 (mod p); that, if

p = 3-2"'-M=g2+3r2, qx-]-ry = l,

{ — l+qy — 3rx)5i^/2 is a primitive root of p; and analogous theorems. If
a and 2a-^l are primes, 2 or a is a primitive root of 2a -fl, according as a
is of the form 4n-[-l or 4n+3. If a is a prime 9^3 and if p = 2a4-l is a
prime and m> 1, then 3 is a primitive root of p unless 3^'"~^-|-l=0 (mod p).
[Cf. Smith.''^]

P. Buttel^ attributed to Scheffler (Die unbestimmte Analytik, 1854,
§142) the method of Crelle^^ for finding the residues of powers.

C. G. Reuschle's^^ table C gives the Haupt-exponent {i. e., exponent to
which the number belongs) (a) of 10, 2, 3, 5, 6, 7 with respect to all primes
p< 1000, and the least primitive root of p; (b) of 10 and 2 for 1000< p< 5000
and a convenient primitive root; (c) of 10 for 5000<p< 15000 (no primitive
root given). Numerous errata have been listed by Cunningham.""

Allegret^^ stated that if n is odd, n is not a primitive root of a prime
2^^n-f-l, X>0; proof can be made as in Lebesgue.^^

"Comptes Rendus Paris, 39, 1854, 1069-71; same in Jour, de Math., 19, 1854, 334-6.
**Proprietades geraes et resolu^ao directa das Congruencias binomias, Lisbon, 1854. Report

by C. Alasia, Rivista di Fisica, Mat. e Sc. Nat., Pavia, 4, 1903, 25, 27-28; and Annaes

Scientificos Acad. Polyt. do Porto, Coimbra, 4, 1909, 166-192.
**'Troi8i&me m6moire sur la thdorie des nombres, Paris, 1854, 24 pp.
"Jour, fiir Math., 49, 1855, 161-86.
"Archiv Math. Phys., 26, 1856, 247.
"Math. Abhandlung. . .Tabellen, Prog. Stuttgart, 1856; full title in the chapter on perfect

numbers. i''^
"Nouv. Ann. Math., 16, 1857, 309-310.

Chap. VII] PRIMITIVE RoOTS, EXPONENTS, INDICES. 191

H. J. S. Smith^^ stated that some of Oltramare's^^ general results are
erroneous at least in expression, and gave a simple proof that 0^"^= 1 (mod p**)
has exactly d roots if d divides 0(p").

V. A. Lebesgue^^ proved that, if p is an odd prime and a, b belong to
exponents a, (3, there exist numbers belonging to the 1. c. m. m of a, (3, as
exponent. Hence if neither a nor /3 is a multiple of the other, w exceeds
a and /3. If d<p — l is the greatest of the exponents to which 1, . . ., p — 1
belong, the latter do not all belong to exponents dividing d, since otherwise
they would give more than d roots of x'^=l (mod p). Hence there exist
primitive roots of p. If a is odd, ±l+2°a belongs to the exponent 2™~"
modulo 2"" (p. 87). If h belongs to the exponent k modulo p, a prime, then
h+Pz belongs modulo p" to an exponent which divides A;p"~^ (p. 101). If
/ is a primitive root of p, and f^~^ — l=pz, then / is a primitive root of p™
if and only if z is not divisible by p (p. 102).

G. L. Dirichlet^^ proved the last theorem and explained his^^ system of
indices for a composite modulus.

V. A. Lebesgue^° published tables, constructed by J. Hoiiel,^^ of indices
and corresponding numbers for each prime and power of prime modulus
< 200, which differ from Jacobi's^^ only in the choice of the least primitive
root. There is an auxiliary table of the indices of x\ for prime moduli
<200.

V. A. Lebesgue^^ stated that, if g'<p is a primitive root of the prime p
and if g'=g^~^ (mod p), then g' is a primitive root of p; at least one of g and
g' is a primitive root of p" for n arbitrary.

V. Bouniakowsky^^ proved in a new way the theorems of Tchebychef^*
that 2 is a primitive root of p = 8n+3 if p and 4n+l are primes, and of
p = 4nH-l if p and n are primes. He gave a method to find the exponent
to which 2 or 10 belongs modulo p.

A. Cayley^^ gave a specimen table showing the indices a, j3,. . . for every
number M = a"6^. . .(modiV), where ilf<iV and prime to iV, for iV = l,. . ., 50.
There is no apparent way of forming another single table for all A^'s analo-
gous to Jacobi's tables (one for each N) of numbers corresponding to given
indices.

F. W. A. Heime^^ gave the least primitive root of each prime < 1000.
His other results are not new. A secondary root of a prime p is one belong-
ing to an exponent < p — 1 modulo p.

"British Assoc. Report, 1859, 228; 1860, 120, §73; Coll. Math. Papers, 1, 50, 158 (Report on
theory of numbers).

**Introd. th^orie des nombres, 1862, 94-96.

"Zahlentheorie, §§128-131, 1863; ed. 2, 1871; ed. 3, 1879; ed. 4, 1894.

soM^m. soc. sc. phys. et nat. de Bordeaux, 3, cah. 2, 1864-5, 231-274.

"Formiiles et tables numer., Paris, 1866. For moduli ^ 347.

^Comptes Rendus Paris, 64, 1867, 1268-9.

"Bull. Ac. Sc. St. Petersbourg, 11, 1867, 97-123.

"Quart. Jour. Math., 9, 1868, 95-96.

"Untersuchungen, besonders in Bezug auf relative Primzahlen, primitive u. secundare Wurzeln,
quadratische Reste u. Nichtreste; nebst Berechnung der kleinsten primitiven Wurzeln
vorf alien Primzahlen zwischen 1 und 1000. BerUn, 1868; ed. 2, 1869.

192 History of the Theory of Numbers. [Chap, vii

C. J. D. Hill^^ noted that his tables of indices for the moduU 2" and 5"
(n^5) give the residues of numbers modulo 10", i. e., the last n digits.
Using also tables for the moduli 9091 and 9901, as well as a table of loga-
rithms, we are able to determine the last 22 digits.

B. M. Goldberg^^ gave the least primitive root of each prime < 10160.

V. Bouniakowsky^^ proved that 3 is a primitive root of p if p = 24n+5
and (p — 1)/4 are primes; —3 is a primitive root of p if p = 12n+ll and
(p — 1)/2 are primes; if p is a primitive root of the prime p = 4n+l, one
(or both) of p, p—p is a primitive root of p"' and of 2p"'; 5 is a primitive
root of p = 20?i+3 or 20n4-7 if p and {p — 1)/2 are primes, and of p = 40n + 13
or 4071-1-37 if p and (p — 1)/4 are primes; 6 is a primitive root of a prime
24n-|-ll and —6 of 24n-|-23 if (p — 1)/2 is a prime; 10 is a primitive root
of p = 40n+7, 19, 23, and -10 of p = 40n+3, 27, 39, if (p-l)/2 is a prime;
10 is a primitive root of a prime 80n-(-73, n>0, or 80n+57, n>l, if
(p — 1)/8 is a prime. If p = 8an-h2a — 1 or 8an+a— 2 and (p — 1)/4 are
primes, and if a^-f-1 is not divisible by p, a is a primitive root of p.

V. A. Lebesgue^^ proved certain theorems due to Jacobi^^ and the
following theorem which gives a method different from Jacobi's for forming
a table of indices for a prime modulus p: If a belongs to the exponent n,
and if 6 is not in the period of a, and if / is the least positive exponent for
which h^=a\ then x^=a has the root a'6", where ft-\-iu — l=nv; the root
belongs to the exponent nf if and only if u is prime to /.

Consider the congruence x*" = a (mod p) , where a belongs to the exponent
n = (p — l)/n', and m is a divisor of n'. Every root r has a period of mn
terms if no one of the residues of r, r^,. . ., r*""^ is in the period of a. If all
the prime divisors of m divide n, the m roots have a period of mn terms;
but if m has prime divisors g, r, . . . , not dividing n, there are only

-(^X^)-

roots having a period of mn terms. The existence of primitive roots follows;
this is already the case if m = n'.

Mention is made of companion tables in manuscript giving indices of
numbers, and numbers corresponding to indices, constructed by J. Ch.
Dupain in full for p<200, but from 200 to 1500 with reduction to one-half
in view of ind p — a=ind a=t(p — 1)/2 modulo p — 1.

L. Kronecker^^ proved the existence of two series of positive integers
Qj, m, {j=l,. . ., p) such that the least positive residues modulo A:>2 of
^1 V2*' • • ■ ^p*" give all the (f){k) positive integers <A: and prime to k, if
ii=0, 1,. . ., mi — 1; i2 = 0, 1,. . ., m2 — 1; etc. [cf. Mertens^^].

G. Barillari^"" proved that, if a is prime to h and belongs to the exponent

"Jour, fur Math., 70, 1869, 282-8; Acta Univ. Lundensis, Lund, 1, 1864 (Math.), No. 6, 18 pp.

"Rest- und Quotient-Rechnung, Hamburg, 1869, 97-138.

"BuU. Ac. Sc. St. P6tersbourg, 14, 1869, 375-81.

»«Compte8 Rendua Paris, 70, 1870, 1243-1251.

"Monatsber. Ak. BerUn, 1870, 881. Cf. Traub, Archiv Math. Phys., 37, 1861, 278-94.

•KJiomale di Mat., 9, 1871, 125-135.

Chap. VII] PrBIITIVE RoOTS, EXPONENTS, INDICES. 193

m modulo h, and if h^ is the highest power of h which divides a"* — 1, and if
n^/i, then 6" divides a* — 1 where e = m6"~\ Further, if 6 is a prime, a
belongs to the exponent e modulo 6". For a new prime 6', let m', n', h'
have the corresponding properties. Then the exponent to which a belongs
modulo B = })%'"' ... is the 1. c. m. L of m6''-\ m'b'"'-''', .... For a = 10, we
see that L is the length of the period for the irreducible fraction N/B.

L. Sancery^^ proved that if p is a prime and a<p belongs to the exponent
6 modulo p, there exists an infinitude of numbers a-\-px = A such that A^—1
is divisible by p^, but not by p'''^^, where k is any assigned positive integer.
If A belongs to the exponent 6 modulo p>2, A will belong to the exponent
6 modulo p" if the highest power of p which divides .A^ — 1 is ^p"; but if it
be p"'^, A belongs to the exponent dp^ modulo p" [Barillari^°"]. Hence A
is a primitive root of p" if a primitive root of p and if A^~^ — 1 is not divisible
by p^, and there are ^j^CpOj primitive roots of p" or 2p\ [Generalization
of Arndt.^^j

C. A. Laisant®^ noted that if a belongs to the exponent 3 modulo p, a
prime, then a + 1 belongs to the exponent 6, and conversely. If a belongs to
the exponent 6, a+1 will not belong to the exponent 3 unless p = 7, a = 3.
Hence if p is a prime 6m +1, there are two numbers a, h belonging to the
exponent 3, and two numbers a + 1, 6+1 belonging to the exponent 6; also,
a+6 = p — 1. If (p. 399) p+5 is an odd prime and p is even, then pV— 9>
p^qP = p (mod p+g).

G. Bella vitis^^'' gave, for each power p'^383 of a prime p, the periodic
fraction for 1/p' to the base 2 and showed how to deduce the indices of
numbers for the modulus p\ Let ? = p'~^(p — 1) and let 2 belong to the
exponent q/r modulo p\ A root b of 6'"= 2 (mod p') is the base of the
system of indices.

G. Frattini^^ proved by the theory of roots of unity that, if p is a prime,
the number of interchanges necessary to pass from 1, 2, . . ., p — 2 to ind 2,
ind 3, . . . , ind (p — 1) and to

ind 1— ind 2, ind 2 — ind 3, . . ., ind (p — 2)— ind (p — 1)

are both even or both odd.

Fritz Hofmann^^ used rotations of regular polygons to prove theorems
on the sum of the primitive roots of a prime (Gauss^).

A. R. Forsyth^^ found the sum of the cth powers of the primitive roots
of a prime p. The sum is divisible by p if p — 1 contains the square of a
prime not dividing c or if it contains a prime dividing c but with an exponent
exceeding by at least 2 its exponent in c. If neither of these conditions is
satisfied, the result is not so simple.

"BuU. Soc. Math, de France, 4, 1875-6, 23-29.

fi^M^m. Soc. So. Phys. et Nat. de Bordeaux, (2), 1, 1876, 400-2.

"^lAtti Accad. Lincei, Mem. Sc. Fis. Mat., (3), 1, 1876-7, 778-800.

"Giornale di Mat., 18, 1880, 369-76.

"Math. Annalen, 20, 1882, 471-86.

^'Messenger of Math., 13, 1883-4, 180-5.

194 History of the Theory of Numbers. [Chap, vii

J. Perott^^ gave a simple proof that x^ = l (mod p") has p'' roots. Thus
there exists an integer b belonging to the exponent p""^ modulo p"*. Assum-
ing the existence of a primitive root of p, we employ a power of it and obtain
a number a belonging to the exponent p — 1 modulo p". Hence ab is a
primitive root of p".

Schwartz^" stated, and Hacken proved, the final theorem of Cauchy.^*

L. Gegenbauer^^ stated 19 theorems of which a specimen is the follow-
mg: If p = 8a(8/3+l) + 24/3+5 and (p-l)/4 are primes and if 64a2+48a
+ 10 is relatively prime to p, then 8a+3 is a primitive root of p.

G. Wertheim^^ gave the least primitive root of each prime < 1000 and
companion tables of indices and numbers for primes < 100. He reproduced
(pp. 125-130) arts. 80-81 of Gauss^ and stated the generalization by
Stern.i^

H. Keferstein''' would obtain all primitive roots of a prime p by excluding
all residues of powers with exponents dividing p — 1 [Poinsot^].

IM. F. Daniels"^ gave a proof like Legendre's^ that there are <f>{n) num-
bers belonging to the exponent n modulo p, a prime, if n divides p — 1.

*K. Szily^- discussed the "comparative number" of primitive roots.

E. Lucas"^ gave the name reduced indicator of n to Cauchy's^^ maximum
indicator of n, and noted that it is a divisor <4){n) of 0(n) except when
n = 2, 4, p* or 2p^', where p is an odd prime, and then equals (f>{n). The
exponent to which a belongs modulo m is called the "gaussien" of a modulo
m (preface, xv, and p. 440).

H. Scheffler"'* gave, without reference, the theorem due to' Richelot^'^ and
the final one by Prouhet.^- To test if a proposed number a is a primitive
root of a prime p, note whether p is of one of the linear forms of primes for
which a is a quadratic non-residue, and, if so, raise a to the powders whose
exponents divide (p — 1)/2.

L. Contejean^^ noted that the argument in Serret's Algebre, 2, No. 318,
leads to the following result [for the case a = 10]: If p is an odd prime and
a belongs to the exponent e = {p — l)/q modulo p, it belongs to the exponent
p-'^e modulo p" when (a*— l)/p is not di\dsible by p, but to a smaller
exponent if it is divisible by p [Sancery®^].

P. Bachmann^^ proved the existence of a primitive root of a prime p
by use of the group of the residues 1, . . . , p — 1 under multiplication.

**Bull. des Sc. Math., 9, I, 1885, 21-24. For k = n — l the theorem is contained imphcitly in a

posthumous fragment by Gauss, Werke, 2, 266.
"Mathesis, 6, 1886, 280; 7, 1887, 124-5.
«8Sitzungsber. Ak. Wiss. Wien (Math.), 95, II, 1887, 843-5.
"Elemente der Zahlentheorie, 1887, 116, 375-381.
'"Mitt. Math. Gesell. Hamburg, 1, 1889, 256.
^'Lineaire Congruenties, Diss., Amsterdam, 1890, 92-99.
"Math, ^s termes ^rtesito (Memou^ Hungarian Ac. Sc), 9, 1891, 264; 10, 1892, 19. Magyar

Tudom. Ak. Ertesitoje (Report of Hungarian Ac. Sc), 2, 1891, 478.
"Th^orie des nombres, 1891, 429.
'*Beitrage zur Zahlentheorie, 1891, 135-143.
"Bull. Soc. Philomathique de Paris, (8), 4, 1891-2, 66-70.
"Die Elemente der Zahlentheorie, 1892, 89.

Chap. VII] PeIMITIVE RoOTS, EXPONENTS, INDICES. 195

G. B. Mathews'^^ reproduced art. 81 of Gauss''' and gave a second proof
by use of Cauchy's^^ congruence X=0 for n = p — 1.

K. Zsigmondy^^ treated the problem to find all integers K, relatively
prime to given integers a and 6, such that a''=b'' (mod K) holds for the
given integral value <T = y, but for no smaller value. For 6 = 1, it is a
question of the moduli K with respect to which a belongs to the exponent y.
Set y=Ilqi*, where the q's are distinct primes and qi the greatest. Then
all the primes K for which a''=b'' (mod K) holds for (T = 7, but for no smaller
a, coincide with the prime factors of

y y

(a^-6^)n(a««'-6««'). . .
A =

n(a^/«-6^/«)...

in which the products extend over the combinations of qi,q2,--- one, two, . . .
at a time, provided that, if a''=h'' (mod qi) for (J=^ylqi\ but for no smaller
(T, we do not include among the K's the prime q^, which then occurs in A
to the first power only. If the prime p is a K and if p^ is the highest power
of p dividing A, then p* is the highest power of p giving a K. The com-
posite i^'s are now easily found. If a and 6 are not both numerically equal
to unity, it is shown that there is at least one prime K except in the following
cases: 7 = 1, a-6 = l; 7 = 2, 0+6 = ^2" (/x^l); 7 = 3, a = ±2, 6==f1;
7 = 6, a = ='=2, 6 = ±l. The case h = \ shows that, apart from the corre-
sponding exceptions, there exists a prime with respect to which the given
integer aj^^^X belongs to the given exponent 7. As a corollary, every
arithmetical progression of the type mT+I ()" = 1? 2, . . .) contains an infini-
tude of primes.

Zsigmondy^^ considered the function A^(a) obtained from the above A
by setting 6 = 1. If a is a primitive root of the prime p = l+7, the main
theorem of the last paper shows that p divides A^(a). Conversely, I+7 is
a prime if it divides A. Thus, if all the primes of a set of integers possess
the same primitive root a, any integer p of the set is a prime if and only if
Ap_i(a) is divisible by p. Hence theorems due to Tchebychef^^ imply
criteria for primes. For example, a prime 2^"+l has the primitive root 3
implies that 2^"+l is a prime if and only if it divides 3^ + 1, where k = 2^'' .
Since ±2 is a primitive root of any prime 2q-\rX such that g- is a prime
4/c± 1, we infer that, if g is a prime 4/c± 1, then 2g+l is a prime if and only
if it divides (2^±1)/(2±1). Since 2 is a primitive root of a prime 4A''+1
such that N is an odd prime, we infer that, if N is an odd prime, 4A^+1 is a
prime if and only if it divides (2^^-|-l)/5.

G. F. Bennett^° proved (pp. 196-7) the first theorem of Cauchy,^^ and
(pp. 199-201) the results of Sancery.^^ If a and a' belong to exponents
t and t' which contain no prime factor raised to the same power in each,
then the exponent to which aa' belongs is the 1. c. m. of t and t' (p. 194).

"Theory of Numbers, 1892, 23-25.

"Monatshefte Math. Phys., 3, 1892, 265-284.

'Hhid., 4, 1893, 79-80.

8»Phil. Trans. R. Sec. London, 184 A, 1893, 189-245.

196 History of the Theory of Numbers. [Chap, vii

If 2*'^^ is the highest power of 2 dividing a^ — 1, where a is odd, the exponent
to which a belongs modulo 2^ is 2^~' if X>s, but, if X^s, is 1 if a=l, 2 if
o^=l, a^l (mod 2^^); the result of Lebesgue'*^ (p. 87) now follows (pp.
202-6) . In case a is not prime to the modulus, there is an evident theorem
on the earliest power of a congruent to a higher power (p. 209). If e is a
given divisor of 0(w), there is determined the number of integers belonging
to exponent e modulo m [cf. Erlerus^^]. If a, a',. . . belong to the exponents
t, t',... and if no two of the «' . . . numbers a'a"' . . . {0^r<t,0^r'<t',. . .)
are congruent modulo m, then a, a', . . . are called independent generators
of the 4>{m) integers <m and prime to m (p. 195); a particular set of
generators is given and the most general set is investigated (pp. 220-241)
[a special problem on abelian groups].

J. Perott^^ found a number belonging to an exponent which is the 1. c. m.
of the exponents to which given numbers belong. If, for a prime modulus p,
a belongs to an exponent t>l, and b to an exponent which divides t, then b
is congruent to a power of a (proof by use of Newton's relations between
the sums of like powers of a, . . . , a' and their elementary symmetric func-
tions). Hence there exists a primitive root of p.

M. Frolo . ^- noted that all the quadratic non-residues of a prime modulus
m are primitive roots of m if m = 2^''4-l, m = 2n+l or 4n + l with n an odd
prime [Tchebychef^^]. To find primitive roots of m "without any trial,"
separate the m — 1 integers <m into sets of fours a, b, —a, —b, where
a6=l (mod m): Begin with one such set, say 1, 1, —1, —1. Either a or
m — a is even; divide the even one by 2 and multiply the corresponding
=t 6 by 2 ; we get another set of four. Repeat the process. If the resulting
series of sets contains all m — 1 integers <m, 2 and —2 are primitive roots
if w = 4/i+l, and one of them is a primitive root if m = 4/i — 1. If the sets
just obtained do not include all m — 1 integers <m, further theorems are
proved.

G. Wertheim^^ gave the least primitive root of each prime p <3000.

L. Gegenbauer^^" gave two expressions for the sum Sk of those terms of a
complete set of residues modulo p which belong to the exponent k, and
evaluated l>Sk/t fit) with t ranging over the divisors of k.

G. Wertheim^^ proved that any prime 2'*" + l has the primitive root 7.
If p = 2"g-|-l is a prime and ^ is a prime >2, any quadratic non-residue m
of p is a primitive root of p if m"" — 1 is not divisible by p. As corollaries,
we get primes q of certain linear forms for which 2, 5, 7 are primitive roots
of a prime 2^-1-1 or 4g-f-l; also, 3 is a primitive root of all primes 8g-|-l
or 16g+l except 41; and cases when 5 or 7 is a primitive root of primes
8^+1, lQq+1. There is given a table showing the least primitive root of
each prime between 3000 and 3500.

"BuU. des Sc. Math., (2), 17, I, 1893, 66-83.

""BuU. Soc. Math, de France, 21, 1893, 113-128; 22, 1894, 241-5.

"Acta Mathematica, 17, 1893, 315-20; correction, 22, 1899, 200 (10 for p = 1021).

8"Denkschr. Ak. Wiss. Wien (Math.), 60, 1893, 48-60.

"Zeitschrift Math. Naturw. Unterricht, 25, 1894, 81-97.

Chap. VII] PRIMITIVE RoOTS, EXPONENTS, INDICES. 197

J. Perott^^ employed the sum Sk of the ^th powers of 1, 2, . . ., p — 1, and
gave a new proof that Si=0, . . ., Sp_2=0, Sp_i= —1 (mod p). If m is the
1. c. m. of the exponents to which 1,2,. . ., p — 1 belong, evidently Sm=p — 1,
whence m>p — 2. If A belongs to the exponent m, then A, A^, . . ., A"" are
incongruent, whence mSp — 1- Thus A is a primitive root.

N. Amici^^ proved that, if j'>2, a number belongs to the exponent 2""^
modulo 2" if and only if it is of the form 8/i±3, and called such numbers
quasi primitive roots of 2\ For a base Sh=^S, numbers of the two forms
8A:+1 or 8^=*=3, and no others, have indices. The product of two numbers
having indices has an index which is congruent modulo 2""^ to the sum of
the indices of the factors. The product of two numbers 6i and 62? neither
with an index, has an index congruent modulo 2""^ to the sum of the indices
of —61 and —62- The product of a number with an index by one without
an index has no index.

K. Zsigmondy^^ proved by use of abelian groups that, if 8 = qi^\ . .Qr'"',
m = pi'^K . .ps^s, where Qi,. . ., Qr are distinct primes, and Pi,..., Ps are dis-
tinct primes, the number of incongruent integers belonging to the exponent
5 modulo m is

5i...5,n(l-l/g/0,
1=1

where d, is the g. c. d. of 5 and tj=(f>{pp), while li is the number of the
integers ti,...,ts which contain the factor ql'K

E. de Jonquieres^^ proved that the product of an even number of primi-
tive roots of a prime p is never a primitive root, while the product of an
odd number of them is either a primitive root or belongs to an exponent not
dividing {p — l)/2. Similar results hold for products of numbers belonging
to like exponents. Certain of the n integers r, for which f is a given num-
ber belonging to the exponent e = {p — \)/n, belong to the exponent ne,
while the others (if any are left) belong to an exponent ke, where k divides n.
He conjectured that 2 is not a primitive root of a prime p=l, 7, 17 or 23
(mod 24); 3 not of p=l, 11, 13 or 23 (mod 24); 5 not of p=\, 11, 19, or
29 (mod 30). These results and analogous ones for 7 and 11 were shown
by him and T. Pepin^^ to follow from the quadratic reciprocity law and
Gauss' theorems on the divisors oi x^^A.

G. Wertheim^°. added to his^* corollaries cases when 6, 10, 11, 13 are
primitive roots of primes 2^+1, 4^+1; also, 10 is a primitive root of all
primes 8g+l?^137 for which g- is a prime 10A;+7 or lOyc+9, and of primes
IGg+l for which g is a prime 10/c+l or lO/c+7.

Wertheim^^ gave the least primitive root of each prime between 3000 and
5000 and of certain higher primes. He noted errata in his^^ table to 3000.

85BuU. des Sc. Math6matiques, 18, I, 1894, 64-66.

8«Rendiconti Circolo Mat. di Palermo, 8, 1894, 187-201.

"Monatshefte Math. Phys., 7, 1896, 271-2.

88Compte8 Rendus Paris, 122, 1896, p. 1451, p. 1513; 124, 1897, p. 334, p. 428.

8»Comptes Rendus Paris, 123, 1896, pp. 374, 405, 683, 737.

'"Acta Math., 20, 1896, 143-152.

"/bid., 153-7; corrections, 22, 1899, 200.

198 History of the Theory of Numbers. [Chap, vn

F. Mertens^- called I'l,. . ., ip the system of indices of n modulo k if
n=gi\ . .qj" (mod A:) for the g's of Kronecker.^° Such systems of indices
differ from Dirichlet's.

C. Moreau^^ set A^ = pV . . . , v = p''~^q^~^ . . . , where p, q,... are distinct
primes. Take € = 1 if iV" is not divisible by 4 or if N = 4, but e = 2 if iV is
divisible by 4 and A'' > 4. Let \p{N) denote the 1. c. m. of v/e, p — l,q — l,. . .
[equivalent to Cauehy's-^ maximum indicator for modulus N]. For A
prime to N, A*^^^= 1 (mod N) . If A^ = p'', 2p^ or 4 (so that N has primitive
roots), yp{N) =4>{N) [Lucas^^j^ ^j^^^.^ -^ ^ ^^^^^ ^^ values of A^< 1000 and
certain higher values for which \p{N) has a given value < 100.

A. Cunningham^"* noted that we may often abbre\iate Gauss' method
of finding a primitive root of a prime p by testing whether or not the trial
root a is a primitive root before computing the residues of all powers of a.
The tests are the simple rules to decide whether or not a is a quadratic or
cubic residue of p. If a is both a quadratic non-residue and a cubic non-
residue of p = 3co+l, and if a^^l for every/ dividing p — 1 except /=p — l,
then a is a primitive root.

A. Cunningham^^ gave tables showing the residues of the successive
powers of 2 when divided by each prime or power of prime < 1000, also
companion tables showing the indices x of 2"" whose residues modulo p'' are
1, 2, 3, . . .. The tables are more convenient than Jacobi's Canon-^ (errata
given here) for the problem to find the residue of a given number with
respect to a given power of a prime, but less convenient for finding all roots
of a given order of a given prime. There are given (p. 172) for each power
p^< 1000 of a prime p the factors of 0(p^"), the exponent ^ to which 2 belongs
modulo p'', and the quotient 0/^.

E. Cahen^^ proved that if p is a prime >(32"'^'-l)/2'"+^ and if 5 =
2^+'^p-\-l (7«>0) is a prime, then 3 is a primitive root of q, whereas
Tchebychef^^ had the less advantageous condition p>3^^V2'"+^. Other
related theorems by Tchebychef are proved. There are companion tables
of indices for primes < 200.

G. A. Miller^^ appUed the theory of groups to prove the existence of
primitive roots of p", to show that the primitive roots of p^ are primitive
roots of p", and to determine primitive roots of the prime p.

L. Kronecker^^ discussed the existence of primitive roots, defined sys-
tems of indices and appHed them to the decomposition of fractions into
partial fractions. He developed (pp. 375-388) the theor>^ of exponents to
which numbers belong modulo p, a prime, by use of the primitive factor

"Sitzungsber. Ak. Wien (Math.), 106, II a, 1897, 259.

«Nouv. Ann. Math., (3), 17, 1898, 303.

"Math. Quest. Educat. Times, 73, 1900, 45, 47.

•'A Binary Canon, showing residues of powers of 2 for divisors under 1000, and indices to

residues, London, 1900, 172 pp. Manuscript was described by author. Report British

Assoc, i895, 613. Errata, Cunningham.'"
"filaments de la th^orie des nombres, 1900, 335-9, 375-390.
•'BuU. Amer. Math. Soc, 7, 1901, 350.
•'Vorlesungen liber Zahlentheorie, I, 1901, 416-428.

Chap. VII] PRIMITIVE RoOTS, EXPONENTS, INDICES. 199

Fd{x) of a;'*— 1 (dividing the last but not x'— 1 iorKd). To every divisor
d of p — 1 belong exactly 4>{d) numbers which are the roots of i^d(^)=0
(modp).

P. G. Foglini^^ gave an exposition of known results on primitive roots,
indices, linear congruences, etc. In applying (p. 322) Poinsot's^ method of
finding the primitive roots of a prime p to the case p = 13, it suffices to exclude
the residues of the cubes of the numbers which remain after excluding the
residues of squares; for, if a; is a residue of a square, (x^)®=l and x^ is the
residue of a square.

R. W. D. Christie^"" noted that, if 7 is a primitive root of a prime
p = 4A; — l,the remaining primitive roots are congruent to p — 7 (n = 1, 2, . . . )

A. Cunningham^°^ noted that 3, 5, 6, 7, 10 and 12 are primitive roots of
any prime /^, = 22"+l>5. Also 7^/^^+1 = 0 (mod F^+, >5).

E. I. Grigoriev^"^ noted that a primitive root of a prime p can not equal
a product of an even number of primitive roots [evident].

G. Wertheim^°^ treated the problem to find the numbers belonging to
the exponent equal to the 1. c. m. of m, n, given the numbers belonging to
the exponents m and n, and proved the first theorem of Stern. ^^ He dis-
cussed (pp. 251-3) the relation between indices to two bases and proved
(pp. 258, 402-3) that the sum of the indices of a number for the various
primitive roots of w = p" or 2p" equals ^4){m)4> ]0(w) \ ■ If « belongs to the
exponent 45 modulo p, the same is true of p — a (p. 266). He gave a table
showing the least primitive root of each prime < 6200 and for certain larger
primes; also tables of indices for primes < 100.

P. Bachmann^°^ gave a generalization (corrected on p. 402) of Stern's^^
first theorem.

G. Arnoux^°^ constructed tables of residues of powers and tables of
indices for low composite moduli.

A. Bindoni^°^ noted that a table showing the exponent to which a belongs
modulo p, a prime, can be extended to a table modulo N by means of the
following theorems. Let a, 61,..., &„ be relatively prime by twos. A
number belonging to the exponent ti modulo bi belongs modulo 6162 ■ ■ -K
to the 1. c. m. of ^1, . . . , ^^ as exponent. If ti is the least exponent for which
a'''+l=0 (mod bi) and if the ti are all odd, the least t for which a'+l is
divisible by 6], ... , 6„ is the 1. c. m. of ^i, . . . , i„. If p is an odd prime not
dividing a and if a belongs to the exponent t modulo p, and a' = pg+l, and
if p" is the highest power of p dividing q, then a belongs to the exponent
lpn~i-u jjiojuio p". Hence if a is a primitive root of p, it is one of p" if

s'Memorie Pont. Ac. Nuovi Lincei, 18, 1901, 261-348.
^""Math. Quest. Educat. Times, 1, 1902, 90.
"i/6id., pp. 108, 116.

"^Kazani Izv. fiz. mat. obsc, BuU. Phys. Math. Soc. Kasan, (2), 12, 1902, No. 1, 7-10.
"'Anfangsgrunde der Zahlenlehre, 1902, 236-7, 259-262.
ii^Niedere Zahlentheorie, 1, 1902, 333-6.
"'Assoc. fran§. av. sc, 32, 1903, II, 65-114.
"«I1 Boll, di Matematica Giorn. Sc. Didat., Bologna, 4, 1905, 88-92.

200 History of the Theory of Numbers. [Chap, vii

and only if a""^ — 1 is not divisible by p^. If t is even, the least x for which
a"+l = 0 (mod p") is l^p""'"".

]\I. Cipolla^°^gave a historical report on congruences (especially binomial),
primitive roots, exponents, indices (in Peano's symboUsm).

K. P. Nordlund^°^ proved by use of Fermat's theorem that, if rij, . . ., n,.
are distinct odd primes, no one dividing a, then A^" = ni"*' . . . n^*"' divides
a'-l, where A;=0(iV)/2^-^

R. D. Carmichael^°^ proved that the maximum indicator of any odd
number is even; that of a number, whose least prime factor is of the form
4ZH-1, is a multiple of 4; that of p(2p — 1) is a multiple of 4 if p and 2p — 1
are odd primes.

A. Cunningham^^° gave a table of the values of v, where {p — l)/v is the
exponent to which 2 belongs modulo p"< 10000, the omitted values of p
being those for which i' = 1 or 2 and hence are immediately distinguished
by the quadratic character of 2 (extension of his Binary Canon^^). A list
is given of errata in the table by Reuschle.^^ An announcement is made of
the manuscript of tables of the exponents to which 3, 5, 6, 7, 10, 11, 12
belong modulo p"< 10000, and the least positive and negative primitive
roots of each prime < 10000 [now in type and extended in manuscript to
p"< 22000].

A. Cunningham^ ^^ defined the sub-Haupt-exponent ^i of a base q to
modulus m = q°-°y]Q (where 770 is prime to q, and ao^O) to be the exponent to
which q belongs modulo r^o- Similarly, let ^2 be the exponent to which q
belongs modulo 771, where ^i = 5'''i?i; etc. Then the ^'s are the successive
sub-Haupt-exponents, and the train ends with ^,.+1 = 1, corresponding to
77;. = 1 . His table I gives these ^k for bases g = 2, 3, 5 and for various moduli
including the primes < 100.

Paul Epstein^ ^^ desired a function ^{m), called the Haupt-exponent for
modulus m, such that a'''^'"^ = 1 (mod m) for every integer a prime to m and
such that this will not hold for an exponent <\p{m). Thus \f/{m) is merely
Cauchy's^^ maximum indicator. Although reference is made to Lucas, ^^
who gave the correct value of 4^(ni), Epstein's formula requires modification
when m = 4 or 8 since it then gives \p = l, whereas \p = 2. The number
x(w, m) of roots of x''= 1 (mod m) is 2dodi . . .d„ if m is divisible by 4 and if
H is odd, but is di . . . ci„ in the remaining cases, where, for m = 2'*°pi*i . . .pn'"'*,
di is the g. c. d. of jj, and 4>{pi°-^), and do the g. c. d. of fx and 2°""^, when
ao>l. The number of integers belonging to the exponent /x = pV--
modulo m is
\x{m, p°)-x(m, p°-^)[ \x{m, q^)-x{m, (f-^)\. . ..

"^Revue de Math. (Peano), Turin, 8, 1905, 89-117.

"8G6teborgs Kungl. Vetenskaps-Handlingar, (4), 7-8, 1905, 12-14.

"»Amer. Math. Monthly, 13, 1906, 110.

"OQuar. Jour. Math., 37, 1906, 122-145. Manuscript announced in Mess. Math., 33, 1903-4,
145-155 (with list of errata in earUer tables); British Assoc. Report, 1904, 443; I'inter-
m^diaire des math., 16, 1909, 240; 17, 1910, 71. CI. Cunningham."^

"iProc. London Math. Soc, 5, 1907, 237-274.

"^Archiv Math. Phys., (3), 12, 1907, 134-150.

Chap. VII] PRIMITIVE RoOTS, EXPONENTS, INDICES. 201

This formula is simplified in the case tx = \l/{m) and the numbers belonging
to this Haupt-exponent are called primitive roots of m. The primitive
roots of m divide into families of 0(i/'(m)) each, such that any two of one
family are powers of each other modulo m, while no two of different families
are powers of each other. Each family is subdivided. In general, not
every integer prime to m occurs among the residues modulo m of the powers
of the various primitive roots of m.

A. Cunningham"^ considered the exponent ^ to which an odd number q
belongs modulo 2"*; and gave the values of ^ when m^ 3, and when q = 2^12='= 1
(fi odd), m>3. When g' = 2''=Fl and m>x-\-l, the residue of q^^^^ can
usually be expressed in one of the forms 1=f2", 1=f2"=f2^.

G. Fontene"^ determined the numbers N which belong to a given
exponent p"'~''8 modulo p"", where 5 is a given divisor of p — l, and h^l,
without employing a primitive root of p"". li p>2, the conditions are that
N shall belong to the exponent 8 modulo p and that the highest power of
p dividing N^ — 1 shall he p^, l^h^m.

*M. Demeczky"^ discussed primitive roots.

E. Landau"^ proved the existence of primitive roots of powers of odd
primes, discussed systems of indices for any modulus n, and treated the
characters of n.

G. A. Miller"^ noted that the determination of primitive roots of g
corresponds to the problem of finding operators of highest order in the
cyclic group G of order g. By use of the group of isomorphisms of G it is
shown that the primitive roots of g which belong to an exponent 2q, where
q is an odd prime, are given by —a", when a ranges over those integers
between 1 and g/2 which are prime to g. As a corollary, the primitive
roots of a prime 2g+l, where q is an odd prime, are — a^, l<a<g+l.

A. N. Korkine"^ gave a table showing for each prime p<4000 a primitive
root g and certain characters which serve to solve any solvable congruence
x^=a (mod p), where g is a prime dividing p — l. Let q" be the highest
power of q dividing p — 1. The characters of degree q are the solutions of

M« = l, u'' = u, u"' = u',..., (w^"-")' = w(''-2) (mod p)

and hence are the residues of the powers of g^p~'^^^^ for k = l,. . ., a. There
are noted some errors in the Canon of Jacobi^^ and the table of Burckhardt.
Korkine stated that if p is a prime and a belongs to the exponent e = {p — 1)/5,
exactly (f){p — l)/<l>{e) of the roots of a;* = a (mod p) are primitive roots of p.
K. A. Posse"^ remarked that Korkine constructed his table without
knowing of the table by Wertheim,^^and extended Korkine's tables to 10000.

"^Messenger of Math., 37, 1907-8, 162-4.

"*Nouv. Ann. Math., (4), 8, 1908, 193-216.

"^Math 6s Phys. Lapok, Budapest, 17, 1908, 79-86.

ii«Handbuch . . .Verteilung der Primzahlen, I, 1909, 391-414, 478-486.

ii'Amer. Jour. Math., 31, 1909, 42-4.

iisMatem. Shorn. Moskva (Math. Soc. Moscow), 27, 1909, 28-115, 120-137 (in Russian). Cf.

D. A. Grave, 29, 1913, 7-11. The table was reprinted by Posse."*
iio/bid., 116-120, 175-9, 238-257. Reprinted by Posse.»"

202 History of the Theory of Numbers. [Chap, vii

R. D. CarmichaeP^® called a number a primitive X-root modulo n if it
belongs to the exponent X(?i), defined in Ch. Ill, Lucas. ""^ The existence
of primitive X-roots g is proved. The product of those powers of g which
are prhnitive X-roots is = 1 (mod n) if X(n) >2. A method is given to solve
X(x) =a, and the solutions tabulated for a ^24.

C. Posse^-^ noted that in Wertheim's^'^^ table, the primitive root 14
of 2161 should be replaced by 23, while 10 is not a primitive root of 3851.

E. Maillet^^^ described the manuscript table by Chabanel, deposited in
the library of the University of Paris, giving the indices for primes under
10000 and data to determine the number having a given index.

F. Schuh^^^ showed how to form the congruence for the primitive roots
of a prime and gave two further proofs of the existence of primitive roots.
He treated binomial congruences, quadratic residues and made applica-
tions to periodic fractions to any base. For any modulus n, he found the
least m for which x"' = 1 (mod n) holds for every x prime to n, and derived
the solutions ?i of 4>{n) =m, i. e., n's having primitive roots.

F. Schuh^^^ discussed the solution of a;' = 1 (mod p") with the least com-
putation. If X belongs to the exponent q modulo n, the powers of x give
a cycle of 0(g) numbers each with the "period" q. The numbers prime to
n and having the period q may form several such cycles — more than one if
n has no primitive root and q is the maximum period. If n = 2" (a>2), then
g = 2* (s^a — 2) and the number of cycles is 1, 3 or 2 according as s = 0, s = 1
or s>l. In the last case, the cj^cles are formed by 2''~^(2fc+l) =f1.

When q is even, x is said to be of the first or second kind according as
x'''^= — 1 (mod n) or not. If the numbers of a cycle are of the second kind,
we get a new cycle of the second kind by changing the signs of the numbers
of the first cycle. While for moduli n having primitive roots there exist no
numbers of the second kind, when n has no primitive roots and g is a possible
even period, there exist at least two cycles of the second kind and of period
q. Finally, there is given a table showing the number of cycles of each
kind for moduli ^ 150.

M. Kraitchik^^^ gave a table showing for each prime p< 10000 a primi-
tive root of p and the least solutions of 2""=!, 10"= 1 (mod p).

*J. Schumacher^^*^ discussed indices.

L. von Schrutka^^^ noted that, if g, r, . . . are the distinct primes dividing
p — l, where p is a prime, all non-primitive roots of p satisfy

(a;V-l)(xV_i) . . .=0 (mod p).

""Bull. Amer. Math. Soc, 16, 1909-10, 232-7. Also, Theory of Numbers, pp. 71-4.

i^iActa Math., 33, 1910, 405-6.

i=»L'interm6diaire des math., 17, 1910, 19-20.

i23Supplement de Vriend derWiskunde, Culemborg, 22, 1910, 34-114, 166-199, 252-9; 25, 1913,

33-59, 143-159, 228-259.
"*Ibid., 23, 1911, 39-70, 130-159, 230-247.
'"Sphinx-Oedipe, May, 1911, Num^ro Special, pp. 1-10; errata listed p. 122 by Cunningham and

Woodall. Extension to 25000, 1912, 25-9, 39-42, 52-5; errata, 93-4, by Cunningham.
"'Blatter Gymnasiaj-Schulwesen, Miinchen, 47, 1911, 217-9,
"^Monatshefte Math. Phys., 22, 1911, 177-186.

Chap. VII] PRIMITIVE RoOTS, EXPONENTS, INDICES. 203

To this congruence he appHed Hurwitz's^^ method (Ch. VIII) of finding the
number of roots and concluded that there are p — l—(f>(p — l) roots.
Hence there exist 0(p — 1) primitive roots of p.

A. Cunningham and H. J. WoodalP^^ continued to p< 100000 the table
of Cunningham"" of the maximum residue indices j^ of 2 modulo p.

C. Posse^^^ reproduced Korkine's"^ and his own"^ tables and explained
their use in the solution of binomial congruences.

C. Krediet^^o treated x*'=l (mod n) of Lucas/^" Ch. Ill, and called x
a primitive root if it belongs to the exponent cp. The powers of such a
root are placed at equal intervals on a circle for various n's.

G. A. Miller^^^ proved by use of group theory that, if m is arbitrary,
the sum of those integers < m and prime to m which belong to an exponent
divisible by 4 is = 0 (mod m) , and the sum of those belonging to the expo-
nent 2 is = — 1 (mod m), and proved the corresponding theorem by Stern^^
for a prime modulus.

A. Cunningham^^^ tabulated the number of primes p<10^ for which
y belongs to the same exponent modulo p, for y = 2, 3, 5, 6, 7, 10, 11, 12;
and the number of primes p in each 10000 to 10^ for which y (2/ = 2 or 10)
belongs to the same exponent modulo p. Also, for the same ranges on
p and y, the number of primes p for which y''^ 1 (mod p) is solvable, where
A; is a given divisor of p — 1 .

A. Cunningham^^^ stated that he had finished the manuscript of a table
of Haupt-exponents to bases 3, 5, 6, 7, 11, 12 for all prime powers < 15000;
also canons giving at sight the residues of z" modulo p'''< 10000 for z = 2,
r^l00;2 = 3, 5, 7, 10, 11, r^30.

J. Barinaga^^^ considered a number a belonging to the exponent g
modulo p, a prime. If a is not divisible by g, the sum of the ath powers
of the numbers forming the period of a modulo p is divisible by p. The
sum of their products n at a time is congruent to zero modulo p ii n<g,
but to =^"1 ii n = g, according as g is even or odd.

A. Cunningham^^^ listed errata in his Binary Canon^^ and Jacobi's Canon. ^^

G. A. Miller^^^ employed the group formed by the integers <m and
prime to m, combined by multiplication modulo m, to show that, if a
number is = ± 1 (mod 2"^), but not modulo 2^+\ where l<7</3, it belongs
to the exponent 2^~^ modulo 2^. Also, if p is an odd prime, and A^= 1
(mod p), N belongs to the exponent p^~^ modulo p^ if and only if A^" — 1 is
divisible by p^, but not by p^+\ where /3>7^ 1.

»8Quar. Jour. Math., 42, 1911, 241-250; 44, 1913, 41-48, 237-242; 45, 1914, 114-125.

i^Acta Math., 35, 1912, 193-231, 233-252.

""Wiskundig Tijdskrift, Haarlem, 8, 1912, 177-188; 9, 1912, 14-38; 10, 1913, 40-46, 87-97.

(Dutch.)
"lAmer. Math. Monthly, 19, 1912, 41-6.
"2Proc. London Math. Soc, (2), 13, 1914, 258-272.
"'Messenger Math., 45, 1915, 69. Cf. Cunningham.""
"<Annaes Sc. Acad. Polyt. do Porto, 10, 1915, 74-6.
"^Messenger Math., 46, 1916, 57-9, 67-8.
"s/Wd., 101-3.

204 History of the Theory of Numbers. [Chap, vil

A. Cunningham^^^ gave five primes p for which there is a maximum
number of exponents to which the various numbers belong modulo p.

On exponents and indices, see Lebesgue^"'*^ and Bouniakowsky^^^; also
Reuschle^^ of Ch. YI, Bouniakowsky"^ of Ch. XIV, and Calvitti^^ of Ch. XX.

Binomial Congruences.

Bhdscara Achd,rya^*^ (1150 A. D.) found y such that y^ — SO is di\'isible
by 7 by solving ?/" = 7c+30. Changing 30 by multiples of 7, we reach a
perfect square 16 with the root 4. Hence set

7c+30 = (7n+4)2, c = 7n'+8n-2, y = 7n-\-4.

Taking n = 1, we get y = ll. Such a problem is impossible if, after abrading
the absolute term (30 above) by the divisor (7 above) and the addition of
multiples of the divisor, we do not reach a square.

Similarly for the case of a cube, with corresponding conditions for impos-
sibihty (§206, p. 265). For y^ = 5e+Q, abrade 6 by the divisor 5 to get
the cube 1; adding 43-5, we get 216 = 6^. Hence set y = 5n-\-Q.

An anonymous Japanese manuscript^^° of the first part of the eighteenth
century gave a solution of x^ — ky = a by trial. The residues Oi, . . ., ak-\ of
1", . . ., (^ — 1)" modulo k are formed; if a^^a, then x = r. It was noted
that ak-r = 0'r or k—Qr according as k is even or odd, and that the residue
of r" is r times that of r"~^

Matsunaga,^^*^" in the first half of the eighteenth century, solved
a}-\-hx= y^ by expressing 6 as a product mn and finding p, q and A so that
mp — nq=l, 2pa=A (mod n). Then x={Am — 2a)A/n [and y=a — 7nb].
But if Am= 2a, write A-\-n in place of A and proceed as before. Or write
2a+h in the form bQ+R, whence x=2a+b-{Q+l)R. To solve 69+
llx=y'^, consider the successive squares until we reach 5^=3 (mod 11).
Write 2-5+11 in the form 1-11 + 10. Then for a=5, 6= 11, Q= 1, i2= 10,
the preceding expression for x becomes 1, whence 5^+11-1 = 6^. Then
write 2-6+11 in the form 2-11 + 1. Then 23-(2+l)-l = 20 gives 6"+
20-11= 16^, and a;= (256-69)/ll= 17.

L. Euler^^^ proved that, if n divides p — l, where p is a prime, and if
a = c''-\-kp, then (by powering and using Fermat's theorem), a^^~^^^" — l is
divisible by p. Conversely, if a'" — 1 is divisible by the prime p = w7i+l,
we can find an integer y such that a — ?/" is divisible by p. For,

o'"-2/'"'' = (a-2/")Q(^),

and the differences of order mn—n of Q(l), Q(2),. . ., Q{mn) are the same

>"Math. Quest, and Solutions (Ed. Times), 3, 1917, 61-2; corrections, p. 65.

'"Vlja-ganita, §§ 204-5; Algebra, with arith. and mensuration, from the Sanscrit of Brahmegupta

and Bhdscara, transl. by H. T. Colebrooke, London, 1817, pp. 263-4.
""Abhand. Geschichte Math. Wiss., 30, 1912, 237.
^'^Ibid., 234-5.
i"Novi Comm. Acad. Petrop., 7, 1758-9 (1755), p. 49, eeq., §64, §72, §77; Comm. Arith., 1,

270-1, 273. In Novi Comm., 1, 1747-8, p. 20; Comm. Arith., 1, p. 60, he proved the first

statement and stated the converse

Chap. VII] BiNOMIAL CONGRUENCES. 205

as those of the term t/'""-" for ?/ = !,..., mn, and hence equal {mn — n)\,
so that Q(y) is not divisible by p for some values 1, . . . , mn of y.

Euler^^^ recurred to the subject. The main conclusion here and from
his former paper is the criterion that, if p = mn-]-l is a prime, x''=a (mod p)
has exactly n roots or no root, according as a"^=l (mod p) or not. In
particular, there are just m roots of a""^!, and each root a is a residue of
an nth power.

Euler^^^" stated that, if aq-\-h=p'^, all the values of x making ax-\-b b,
square are given by a;= ay'^^2py-\-q.

J. L. Lagrange^^^ gave the criterion of Euler, and noted that if p is a
prime 4n+3, B'-^'^^^^ — l is divisible by p, so that x=B'''^^ is a root of
x^=B (mod p). Given a root ^ of the latter, where now p is any odd prime
not dividing B, we can find a root of x^=B (mod p^) by setting x = ^-\-\p,
i^-B = poi. Then x^-B = {\^-{-n)p'^ if 2|X+co=MP. The latter can be
satisfied by integers X, jjl since 2^ and p are relatively prime. We can pro-
ceed similarly and solve x^=B (mod p").

Next, consider ^^=B (mod 2"), for n>2 and B odd (since the case B
even reduces to the former). Then ^ = 2z-\-l, ^^ — B = Z-\-\—B, where
Z = 4:z{z-\-l) is a multiple of 8. Thus 1—B must be a multiple of 8. Let
w>3 and 1-B = 2'^,r>3. If r^n, it suflaces to take 2 = 2""^, where f is
arbitrary. If r<n, Z must be divisible by 2'', whence 2 = 2'""^^ or 2*""^^ — 1.
Hence w=^{2'-^i:=i=l)-\-p must be divisible by 2"-''. If n-r^r-2, it
suffices to take f =^iS divisible by 2""''. The latter is a necessary condition
if n-r>r-2. Thus ^ = 2'-^p=F^, w = 2'-\f=t=p). Hence f ±p must be
divisible by 2""^'^+^. We have two sub-cases according as the exponent of
2 is ^ or >r — 1; etc.

Finally, the solution of x^=B{mod m) reduces to the case of the powers of
primes dividing m. For, if / and g are relatively prime and ^^ — Bis divisible
by /, and \p^—B by g, then x^—B\b divisible by fg ii x= jif^ ^ = vg^\l/. But
the final equality can be satisfied by integers /z, v since / is prime to g.

A. M. Legendre^^^ proved that if p is a prime and co is the g. c. d. of n
and p — \ = oip', there is no integral root of

(1) a:"=j5(modp)

unless B^'= 1 (mod p) ; if the last condition is satisfied, there are co roots
of (1) and they satisfy

(2) x'^^B^ (mod p),
where I is the least positive integer for which

(3) ln — q{p — \)=o}.

For, from (1) and x''-^=l, we get x^''=B\ x^^^-^^^l, and hence (2), by use
of (3). Set n = oin'. Then, by (2) and (1),

^n'l^^n^2, 5P''=a;P'"=<rP-l=l (mod p) .

"2Novi Comm..Petrop., 8, 1760-1, 74; Opusc. Anal. 1, 1772, 121; Comm. Arith., 1, 274, 487.

"^aOpera postuma, I, 1862, 213-4 (about 1771).

"^Mem. Acad. R. Sc. Berlin, 23, ann6e 1767, 1769; Oeuvres, 2, 497-504.

"^M6m. Ac. R. Sc. Paris, 1785, 468, 476-481. (Cf. Legendre.i^^)

206 History of the Theory of Numbers. [Chap, vii

Since In'—qp' = 1, the first gives 5^"'= 1. Hence

Conversely, if B^'=l,

a^p-i_l=a^p'-_j5p'/ (mod p)

has the factor x" — B\ so that (Lagrange^) congruence (2) has co roots.

If 4n divides p — 1, the roots of x^"= —1 (mod p) are the odd powers of
an integer belonging to the exponent 4n modulo p.

Let n divide p — l, and 7n divide {p — l)/n. Let co be the g. c. d. of
m , n and set n = cov. Determine positive integers I and q such that lv — qm = l.
If 5'"= =•= 1 (mod p), (1) is satisfied by the roots of x'^^B'y (mod p), where
y ranges over the roots of ?/"= (=t 1)^ (mod p). For, the last two congruences
give

x'' = x'"'=B''^y''=B'"^+\=i=iy=B (mod p).

Hence by means of the roots of ?/''=±l, we reduce the solution of (1) to
binomial congruences of lower degrees. In particular, let n = 2, m = (p — 1)/2,
and let 2 be prune to ?«, so that p = 4:a — l,l = a,q = l. Then x^ = B (mod p)
requires that 5"* = 1 , so that we have the solutions .t = =*= 5" without trial
(Lagrange^^^). Next, if n = 2 and 5^'^+^= —1, the theorem gives x = B'''^^y,
where ?/- = — L But we may generalize the last result. Consider x" + c^ = 0
(mod p). Since p must have the form 4a+l, we have p=f^-\-g^. Deter-
mine u and z so that c = gu—pz. Then x = fu (mod p).

Let a belong to the exponent nw modulo p, where w divides (p — l)/n.
Then the roots of B"' = l (mod p) are B = a"*' (m = 1,- • •, w) — 1), and, for a
fixed B, the roots of (1) are x = 0'"""+" (m = 0, 1, . . . , n - 1). For, a" belongs
to the exponent w, whence B = a'"'.

Legendre^^^ gave the same theorems in his text. He added that, know-
ing a root 6 of (1), it is easy to find a root of x" = B (mod p"), with the
possible exception of the case in which n is divisible by p. Let6"—B = Mp
and set a:=^+i4p. Then a;" — 5 is divisible by p^ if

M+'nB''-^A=pM',

which can be satisfied by integers A, Af' if n is not divisible by p. To solve
(1) when p is composite, p = a°6^ . . . , where a, 6, . . . are distinct primes, deter-
mine all the roots X of X" = B (mod a°), all the roots ^ of ijl" = B (mod b^),

Then if x=\ (mod a°), x=iJi (mod 6^),. . ., x will range over all the roots
of (1).

Legendre^^^ noted that if p is a prime 8n+5 we can give explicitly the
solutions of a:^+a = 0 (mod p) when it is solvable, viz., when a'*"''"^ = 1. For,
either «-"+' + 1=0 and x = a"+' is a solution, or a-"+^-l=0 and (9 = a"+^
satisfies d^ — a^O (mod p), so that it remains only to solve x^-\-d' = 0, which
was done at the end of his^^* memoir. For p = 8?i+l, let n = a^, where a
is a power of 2 and /3 is odd; if 0"= ± 1, x^-\-a = 0 can be solved as in the

i"Th(5orie des nombres, 1798, 411-8; ed. 2, 1808, 349-357; ed. 3, 1830, Nos. 339-351; German

transl. by Maser, 1893, 2, pp. 15-22.
^"Ibid., 231-8; ed. 2, 1808, pp. 211-219; Maser, I, pp. 246-7.

Chap. VII] BiNOMIAL CONGEUENCES. 207

case p = 8n+5; but in general no such direct solution is known, and it is
best to represent some multiple of p by the form y'^+az^.

If we have found 6 such that ^^+a is divisible by the prime p, not dividing
a, we readily solve x^+a = 0 (mod p"). For, from

r^-\-as^ is divisible by p^. Now s is not divisible by p. Thus we may take
r = sx+p''y, whence x^+a is divisible by p". [Cf. Tchebychef, Theorie der
Congruenzen, §30.]

The case of any composite modulus N is easily reduced to the preceding
(end of Lagrange's^^^ paper). Legendre proved that, if N is odd and prime
to a, the number of solutions of a:^+a = 0 (mod N) is 2'"^ where i is the
number of distinct prime factors of N; the same is true for modulus 2N.
Henceforth let N be odd or the double of an odd number and let d be the
g. c. d. of N and a. If d has no square factor, the congruence has 2'"^ roots,
where i is the number of distinct odd prime factors of N not dividing a.
But if d=o)\(/^, where co has no square factor, the congruence has 2'~V
roots where i is the number of distinct odd prime factors of N/d.

C. F. Gauss^" treated congruence (1) by the use of indices. However,
we can give a direct solution (arts. 66-68) when a root is known to be con-
gruent to a power of B. For, by (1) and x = B^, B^B^"". If therefore a
relation of the last iy^e is known, a root of (1) is B''. The condition for
the relation is l = A:n (mod t), where t is the exponent to which B belongs
modulo p. It is shown that t must divide m = (p — l)/n. We may discard
from m any factor of n; if the resulting number is m/q, the unique solution
k of 1 = 1:11 (mod m/q) is the desired k. [Cf. Poinsot^^^]

Gauss (arts. 101-5) gave the usual method of reducing the solution of
x^= A (mod m) for any composite modulus to the case of a prime modulus
and gave the number of roots modulo p'* in the various possible subcases.
His well-known and practical ''method of exclusion" (arts. 319-322) employs
successive small powers of primes as moduU. Another method (arts.
327-8) is based on the theory of binary quadratic forms [cf. Smith^^°].

The congruence ax^-\-'bx-\-c=0 (mod m) is reduced (art. 152) to y^=}? —
Aac (mod 4am). For each root y, it remains to solve 2ax-{-b=y (mod 4aw).

Gauss^^^ showed in a somewhat incomplete posthumous paper that, if
t is a prime and f~'^{t — l)=a''¥. . ., where a,h,. . . are distinct primes, the
solution of a:"= 1 (mod t") may be made to depend upon the solution of a
congruences of degree a, jS congruences of degree h, etc. Use is made of the
periods formed of the primitive roots of the congruence, as in Gauss' theory
of roots of unity.

Legendre^^^ solved x^+a=0 (mod 2'") when a is of the form — 1 =F8a by

i"Disquis. Arith., 1801, Arts. 60-65.

"sWerke, 2, 1863, 199-211. Maser's German transl. of Gauss' Disq. Arith., etc., 1889, 589-601

(comments, p. 683).
"'Theorie des nombres, ed. 2, 1808, pp. 358-60 (Nos. 350-2). Maser, 2, 1893, 25-7.

208

History of the Theory of Numbers.

[Chap. VII

use of the expansion of (1+2)^'^:

M

M-3

Vl±8a = l±|2^a-— 7 2V=t— — 2V- . . . =tiV23"a"+ .

N =

M-3-5

2-4

(2n

2-4-6

■3)

2-4-6-8. ..2n

The coefficient of a" is an integer divisible by 2"^^ Retain only the terms
whose coefficients are not divisible by 2'""^ and call their sum 6. Hence
every term of 6~-^a is divisible by 2'". Thus the general solution of the
proposed congruence is x=2'^~^x'^d.

P. S. Laplace^*^" attempted to prove that, if p is a prime and p — l=ae,
there exists an integer x<e such that x' — l is not divisible by p. For, if
x = e and all earlier values of x make a:* — 1 divisible by p,

/=(e^-l)-e^
would be divisible by p.

,{e-lY-l\ + {^^y,{e-2Y-l\-...

The sum of the second terms of the binomials is

+ ... = -(1-1)^ = 0,

while the sum of the first terms of the binomials is e ! by the theory of differ-
ences, and is not divisible by p since e<p. [But the former equality implies
that the last term of / is ( — 1)''(0— 1), whereas the theorem is trivial if x
is allowed to take the value 0. Again, nothing in the proof given prevents
a from being unity; then the statement that there is a positive integer
x<p — l such that x^~^ — 1 is not divisible hyp contradicts Fermat's theorem.]

L. Poinsot^^ deduced roots of a;"= 1 (mod p) from roots of unity.

M. A. Stern^^ (p. 152) proved that if n is odd and p is a prime, rc"= —1
(mod p) is solvable and the number of roots is the g. c. d. of n and p — l;
while, if n is even, it is solvable if and only if the factor 2 occurs in p — 1 to a
higher power than in n.

G. Libri^^^ gave a long formula, involving sums of trigonometric func-
tions, for the number of roots of x^+c=0 (mod p).

V. A. Lebesgue^^ applied a theorem on/(a:i, . . ., Xk) = 0 to derive Legen-
dre's^^^ condition B^'=l for the existence of roots of (1), and the number
of roots. Cf. Lebesgue^^ of Ch. VIII.

Erlerus^^ (pp. 9-13) proved that, if pi, . . . , p^ are distinct odd primes,

x~=l (mod2''p/'...p/)

has 2", 2", 2"+^ or 2"+^ roots according as j/ = 0, 1, 2 or >2.

For the last result and the like number of roots of x^=a, see the reports,
in Ch. Ill on Fermat's theorem, of the papers by Brennecke^^ and Crelle^*
of 1839, Crelle,^^ Poinsot" (erroneous) and Prouhet^^ of 1845, and Schering^''*
of 1882.

C. F. Arndt^^^ proved that the number of roots of x'= 1 (mod p") for

"»Communication to Lacroix, Traitd Calcul Diff. Int., ed. 2, vol. in, 1818, 723.
'"Jour, fur Math., 9, 1832, 175-7. See Libri," Ch. VIII.
"*Archiv Math. Phys., 2, 1842, 10-14, 21-22.

Chap. VII] BiNOMIAL CONGRUENCES. 209

p an odd prime is the g. c. d. of t and (/)(p") ; the same holds for modulus 2p".
He found the number of roots of x'^=r (mod m), m arbitrary. By using
S</>(0 =5, if i ranges over the divisors of 5, he proved (pp. 25-26) the known
result that the number of roots of x"= 1 (mod p) is the g. c. d. 5 of n andp — 1.
The product of the roots of the latter is congruent to ( — 1)*"^^; the sum of
the roots is divisible by p; the sum of the squares of the roots is divisible
bypif 6>2.

P. F. Arndt^^^ used indices to find the number of roots of x^ = a.

A. L. Crelle^^^gave an exposition of known results on binomial congruences.

L. Poinsot^^^ considered the direct solution of x"=A (mod p), where p
is a prime and n is a divisor of p — l=nm (to which the contrary case
reduces). Let the necessary condition ^""=1 be satisfied. Hence we may
replace A by A^+"''^ and obtain the root rc=A^ if l-\-mk = ne is solvable for
integers k, e, which is the case if m and n are relatively prime [cf. Gauss^^^].
The fact that we obtain a single root x=A^ is explained by the remark that
it is a root common to a:"=A and x"'=l, which have a single common root
when n is prime to m. Next, let n and m be not relatively prime. Then
there is no root A' if A belongs to the exponent m modulo p. But if A
belongs to a smaller exponent m' and if m' is prime to n, there exists as
before a root A", where l-\-m'k = ne'. The number of roots of a;"=l
(mod N) is found (pp. 87-101).

C. F. Arndt^^^ proved that x'=l (mod 2"), n>2, has the single root 1 if
t is odd; while for t even the number of roots is double the g. c. d. of i and
2n-2^ The sum of the A:th powers of the roots of x'= 1 (mod p) is divisible
by the prime p if A: is not a multiple of t. By means of Newton's identities
it is shown that the sum, sum of products by twos, threes, etc., of the roots
of x*= 1 (mod p) is divisible by the prime p, while their product is = + 1 or
— 1 according as the number of roots is odd or even. If the sum, sum of
products by twos, threes, etc., of m integers is divisible by the prime p,
while their product is =—( — 1)'", the m integers are the roots of x'"=l
(mod p).

A. Cauchy^" stated that if I = p\'' . . ., where p, q,... are m distinct
primes, and if n is an odd prime, x"= 1 (mod 7) has rf distinct roots, includ-
ing primitive roots, i. e., numbers belonging to the exponent n. [But
x^= 1 (mod 5) has a single root.]

Cauchy^^^ later restricted p, q,. . . to be primes =1 (mod n). Then
a:"=l (mod p^) has a primitive root ri, and rc^^l (mod q") has a primitive
root 7-2, so that x''^ 1 (mod /) has a primitive root, viz., an integer =ri (mod
p*") and =r2 (mod q"), etc.; but no primitive root ii p, q,. . . are not all =1
(mod n).

i«3Von den Kubischen Resten, Torgau, 1842, 12 pp.

»*Jour. fiir Math., 28, 1844, 111-154.

»«Jour. de Math^matiques, (1), 10, 1845, 77-87.

""Archiv Math. Phys., 6, 1845, 380, 396-9.

"'Comptes Rendus Paris, 24, 1847, 996; Oeuvres, (1), 10, 299.

"sComptes Rendus Paris, 25, 1847, 37; Oeuvres, (1), 10, 331.

210 History of the Theory of Numbers. [Chap, vii

Hoen4 Wronski^^^ stated without proof that, if a;'"=a (mod M),

a = {-iy+'\hK+{-lY+''rA[M/K,o)Y-^+Mi,
x = h + (-lY+'A[M/K, iry-'+Mj,

and that M must be a factor of aK"" - \hK-{-iy+^\'". Here the "alephs"
A[M/K, o)Y, for r = 0, 1,. . ., are the numerators of the reduced fractions
obtained in the development of M/K as a continued fraction. In place of
K, Wronski wrote the square of l''^^ = k\. Concerning these formulas, see
Hanegraeff,"^ Bukaty,!^^ Dickstein.^^^ Cf. Wronski^^^ of Ch. VIII.

E. Desmarest" noted that, if x'^+D=0 (mod p) is solvable, x^+Dy^ = mp
can be satisfied by a value of m<3+y>/16 and a value of 2/^3. His proof
is not satisfactory.

D. A. da Silva''^ (Alasia, p. 31) noted that x^^l (mod m), where
m = Pi*'P2^* •• ■ . has the roots 'Zxiqi7n/p{^ where Xi is a root of x^'= 1
(mod Pi"^), Di being the g. c. d. of D and <t){pr), while the g's are integers
such that Xqim/p['=\ (mod m).

Da Silva^^^" proved that a solvable congruence a:"=r (mod m) can be
reduced to the case r prime to m and then to the case m = p'',p a prime > 2.
Then, if 5 is the g. c. d. of n and (f){p'')=8di, there is a root if and only if
r*'=l (mod p") and hence if and only if r'^=l (mod p"'"^^), where p"' is the
g. c. d. of n and p"~"\ while d is the quotient of p — 1 by its g. c. d. with n.

H. J. S. Smith^'^" indicated a simplification in Gauss'^" second method
of solving x^^A, If r^-\-D=0 (mod P) is solvable, mP = x^-\-Dy'^ is solvable
for some value of ?72< 2V-D/3. Employing all values of m under that limit
for which also

(i)=S>

and finding with Gauss all prime representations of the resulting products
by the form x^-\-Dy^, we get ±r=x'/y', x"/y",. . .(mod P), where x', y';
x", y" \. . . denote the sets of solutions of mP = x^-\-Dy^.

Eg. Hanegraeff^^^ reduced x"'=r to d"'r=l (mod p) by use of 6x=l.
When p/d is developed into a continued fraction, let /x and P^_i be the
number of quotients and number of convergents preceding the last. Let v,
P^_i be the corresponding numbers for p/O"". Then

x^i-iy-'P,_„ r=(-ir^P,_i (mod p).

For p a prime, we get all roots by taking 6 = 1,. . . , (p — 1)/2. By starting
with d{x — h)^l in place of 6x= 1, we get

"'R6forme des Math^matiques, being Vol. i of R6forme du savoir humain, 1847. Wronski's
mathematical discoveries have been discussed by S. Dickstein, Bibliotheca Math., (2),
6, 1892, 48-52, 85-90; 7, 1893, 9-14 [on analysis, (2), 8, 1894, 49, 85; (2), 10, 1896, 5].
Bull. Int. Ac. Sc. Cracovie, 1896; Rozprawy, Krakow, 4, 1913, 73, 396. Cf. I'intermd-
diaire des math., 22, 1915, 68; 23, 1916, 113, 164-7, 181-3, 199, 231-4; 25, 1918, 55-7.

"'<KU. Alasia, Annaes Sc. Acad. Polyt. do Porto, 9, 1914, 65-95. There are many confusing
misprints; for example, five at the top of p. 76.

""British Assoc. Report, 1860, 120-, §68; CoU. M. Papers, 1, 148-9.

"*Note BUT r^quation de congruence x^=r (mod p), Paris, 1860.

Chap. VII] BiNOMIAL CONGRUENCES. 211

x-h={-iy-'P,-u r^{-iy-\dh+irP^.^ (mod p).

By taking ^=(1^/')^ and replacing 1 by (-1)^+^ in 0(a;-/i) = l, the last
results become the fundamental formula given without proof by Wronski^^^
in his Reforme des Mathematiques.

G. L. Dirichlet^^^ discussed the solution of x^^D for any modulus.

G. F. Meyer"^ gave an elementary discussion of the solution of x^=b
(mod k), for k a prime, power of prime, or any integer.

V. A. Lebesgue^^^ employed a prime p, a divisor n of p — l=nn', and a
number a belonging to the exponent n' modulo p. Then the roots of
a;" = a (mod p) are a"6^, where h is not in the period of a, and 6 is a quadratic
non-residue of p if a is a quadratic residue, and 6" is the least power of h
congruent to a term of the period of a. If we set 6" = a" (mod p), then
must na-\-v^ = l (mod n'). The roots x are primitive roots of p. In the
construction of a table of indices, his method is to seek a primitive root
giving to ±2 the minimum index (rather than to ±10, used by Jacobi);
thus we use the theorem for a= ±2.

Lebesgue^'^^ gave reasons why the conditions imposed on h in his pre-
ceding paper are necessary. He added that when we have found that
x" = a (mod p) leads to a primitive root x = g oi p,\i is easy to solve x'"=r
(mod p) when m divides p — 1, by expressing r as a power of g by the equiva-
lent of an abridged table of indices.

Lebesgue^^*^ noted that the usual method of solution by indices leads
to the theorem: If a belongs to the exponent e modulo p, and if n divides
p — 1, and we set n = e'm, where e' has only prime factors which divide e,
while m is prime to e, then, for every divisor M of m, x'^^a (mod p) has
e'(j){M) roots belonging to the exponent M.

If a belongs to the exponent e modulo p, there are e0(n) numbers h, not
in the period of a, for which 6"= a' (mod p), with n sl minimum. A common
divisor of n and i does not divide e. Then the n roots of x"= a (mod p) are
a'6", where nt — iu — l = ev, t<e, u<n. This generahzation of his^^'' earlier
theorem is used to find the period of a primitive root of p from the period of 2.

R. Gorgas"^ stated that, if p is the residue modulo M of the pth term of
](M-l)/2[^. . .,2^ 1^, then p(p-l)=p±m+ikf a, according as ilf = 4m=t:l.
Take the lower signs and solve for p ; we get

2p = l±6, 62 = M(4a-l)+4p.

Set 4p = Mc+p'. Hence the initial equation x^ = My+p has been replaced
by 6^ = M(4a-fc — l)+p' of like form. Let p' be the p'th place from the
end. The process may be repeated until we reach an equation P(P — 1)
= MA-\-p^—m solvable by inspection.

"^Zahlentheorie, 1863, §§32-7; ed. 2, 1871; ed. 3, 1879; ed. 4, 1894.

»"Archiv Math. Phys., 43, 1865, 413-36.

"^Comptes Rendus Paris, 61, 1865, 1041-4.

"'Ihid., 62, 1866, 20-23.

"«/6id., 63, 1866, 1100-3.

"^Ueber Losung dioph. Gl. 2. Gr., Progr., Magdeburg, 1867.

212 History of the Theory of Numbers. [Chap, vii

Ladrasch^^^ obtained known results on x^=a for any modulus.

V. Bouniakowsky^"^ gave a method of sohdng q-S'^ ^r (mod P), where
P is odd. His first illustration is 3'==±=1 (mod 25). Write the integers
^(25 — 1)/2 in a line. Under the first four wTite in order the integers
= 0 (mod 3) ; under the next four write in reverse order those = 1 ; under
the last four write in order those = 2.

1* 2* 3* 4*
3 6 9 12

5 6* 7* 8*
10 7 4 1

9* 10 11* 12*
2 5 8 11

Mark with an asterisk 1 in the first line; below it lies 3; mark with an
asterisk 3 in the first line; etc. The number 10 of the integers marked
with an asterisk is the least solution x of 3""= —1 (mod 25). The sign is
determined by the number of integers in the second set marked by an
asterisk. The method applies to any P = 6n+1. But for P = 6n+5, we
use for the second set of numbers in the second line those =2 (mod 3) in
reverse order, and for the third set those =1 in order. If P = 23, we see
that each of the 11 numbers in the first line are marked with an asterisk,
whence 3^^=-l (mod 23). A like marking occurs for P = 5, 11, 17, 29.
For P = 35, 12 numbers are marked, whence 12 is the least x for which
3''=1 (mod 35). Starting with the unmarked number 5, we get the cycle
5, 15, 10, whence 3^= —1 (mod 7); similarly, the cycle 7, 14 gives 3"= —1
(mod 5).

For g'-3'^=='=4 (mod 25), we begin with 4 in the second row. Since it
hes below 7, we mark 7 with an asterisk in the second row; etc. We use an
affix n on the number which is the nth marked by an asterisk.

12 3 4

5

6 7 8

9 10

11 12

3*6 g*3 9*5 12*10

10

7*2^*1 ]^*7

2*^ 5

8*8 11*9

For 5 = 11, we have the entry 8*^ below 11; hence 11-3^=— 4, the sign
following from the number of entries ^ 8 in the second set which are marked
with an asterisk. Similarly for any 5^ 12, except g = 5, 10.

Bukaty^^" discussed the formula of Wronski.^^^

T. N. Thiele^^^ used a mosaic (empty and filled squares on cross-section
paper) to test y^=d{T[\od c), where c is an integer or Gauss complex integer
a + 5v— 1, employing the graph oi y'^ — cx = d.

Dittmar^^^ discussed a;^=r (mod p). Using Cauchy's^* explicit con-
gruence for the numbers belonging to a given exponent, he gave the expanded
form of the congruence with the roots belonging to the successive exponents
1,. ..,21.

"*Von den Kubischen Resten u. Nichtresten, Progr., Dortmund, 1870.

i-'Bull. Ac. Sc. St. Pdterebourg, 14, 1870, 356-375.

i*'>D6duction et demonstration de trois lois primordiales de la congruence des nombres, Paris,

1873.
*""0m Talmonstre," Forhandl. Skandinaviske Naturforskeres, Kjobenhavn, 11, 1873, 192-5.
"^Die Theorie der Reste, insbesondere derer vom 3. Grade, nebst einer Tafel der Kubischen

Reste aller Primzahlen der Form 6m + 1 zwischen den Grenzen 1 und 100. Progr. Koln

Gym., Berlin, 1873.

^li Chap. VII] BiNOMIAL CONGRUENCES. 213

L. Sancery" (pp. 17-23) employed the modulus M = p'' or 2^', where p
is an odd prime. Let a belong to the exponent n modulo M. Let A be the
g. c. d. of m and 4>{M)/n. Set A=AiA2 where Ai = pi*'p2*' • • • > and p,-
is a prime dividing both A and n, and p/< is the power of Pi dividing A.
Let b be any divisor of Ag. Then a:"'=a (mod M) has 0(nAi5)/0(n) roots
belonging to the exponent nAjS ; the power aAi5 of such a root is congruent
to a, where a can be found by means of a linear congruence. Given a
number belonging to the exponent nAi5, we can find Ai5 roots of the con-
gruence.

C. G. Reuschle^^^" tabulated the roots of /=0 (mod p), where p = wX+l
and X are primes and / is the maximum irreducible algebraic prime factor
of a^ — 1; also the roots of

T^Hc^O, r/Hc^^O, TyHc^sO, rf^'n-\-d=Q,

for c<13, d= —1 to —26, d=+2 to +21, and for various cubic and
quartic congruences.

A. Kunerth's method for ^^=c (mod h) will be given in Vol. 2, Ch. XII.
E. Lucas^^^^ treated a;^+l=0 (mod p"), where p is a prime >2, for use

in the question of the number of satins. Given a^+l=0 (mod p), set

{a+i)"' = A+Bi, ^B=l (mod p'").

Then A^ is a root x of the proposed congruence.

B. Stankewitsch^^^ proved that if x^^q (mod p) is solvable, p being an
odd prime, the positive root <p/2 is =B/A (mod p), where

1-2 i

A=Si_,+qSi.3+q%_s+ ...+q^ S^, B = Si+qSi_2+ ■ ■ • +q^

where i = {p — l)/2 and Sk denotes the sum of the products of 1, 2, . . ., i
taken k at a time. Let n be a divisor of p — 1. Let F{x) be the g. c. d.
modulo p of x" — ! and Il(x''^"- — 1), where a ranges over the distinct
prime factors of n. Call f{x) the quotient of x'' — l by i^(a;). Then the
roots of f{x) = 0 (mod p) are the primitive roots of x"= 1 (mod p) . [Cf .
Cauchy.14]

N. V. Bougaief^^^ noted that if p = 8n+5 is a prime and if x^=q
(mod p) is solvable, it has the root g(p+3)/8 ^j. (pzl)! g(p+3)/8 according as
q2n+i^-^ or -1. If p = 2^Z+l, I odd, and q'=l, it has the root x=q^'+'^/\
[Legendre.^^®]

T. Pepin^^^ treated x^= 2 by tables of indices.

P. Gazzaniga^^^ gave a generalization of Gauss' lemma (the case n = 8 = 2,

1820 Tafeln Complexer Primzahlen . . . , Berlin, 1875. Errata, Cunningham."*

^^^^ G6om6trie des tigsus, Assoc, fran^., 40, 1911, 83-6; French transl. of his Italian paper in

I'Ingegnere Civile, 1880, Turm.
is'Moscow Math. Soc, 10, 1882-3, I, 112 (in Russian).
^<^Ibid., p. 103.

"»Atti Accad. Pont. Nuovi Lincei, 38, 1884-5, 201.
"»Atti Reale Istituto Veneto, (6), 4, 1885-6, 1271-9.

214 History of the Theory of Numbers. [Chap, vii

^ = 0). Separate the residues modulo p of kq, for k = l, 2, . . ., {p — l)/d,

into three sets: .':

P 5-1 i

0<ri,. . ., r,<-<Si,. . ., s,<-^p<tu. • ., t^<p j

and form the differences mi = p — t,. From the set 1,. . ., (p — 1)/5, delete
the r, and ?n,; there remain v numbers i\. If ?/, is a root of s,?/,= yi (mod p),
then x"=5 (mod p) is solvable if and only if ( — l)"?/!. . .2/„=l (mod p),
where 5 is the g. c. d. of n and p — 1 .

P. Seelhoff^^^ gave the known cases in which x^=r (mod p) can be
solved explicitly [Lagrange, ^^^ Legendre^^^]. In the remaining cases, one
uses Gauss' method of exclusion, the process of Desmarest,^^ or, with
Seelhoff, use various quadratic residues of p {ibid., p. 306). Here x^=41
(mod 120097) is treated.

A. Berger^^^ considered a quadratic congruence reducible to a:^=D (mod
4n), where D=0 or 1 (mod 4). If D is prime to n, the number of roots is

^(D, in) = 2n{l + (f ) } = 2S (f ) f . = 22 (f ) f,,

where p ranges over the distinct prime factors of n, while d and di range
over the pairs of complementary divisors of n, and f ^ = 0 or 1 according as
d has a square factor or not. If g{nm)=g{n)g{m) for all integers n, m,
ands'(l) = l,

zgy (Z), 4n)^(n) = 22 Q ^(n) -S Q ^(n) -^2 Q ^(n)^
where n ranges over all positive integers. Mean values are found :

J,(?)*»«-;b5ti7S.?,©I«-"

it=i TT h=i\n/n

where A is a fundamental discriminant according to Kronecker, X, Xi are
finite for all n's, and p ranges over all primes.

G. Wertheim^^^ presented the theory of a;^=a (mod m).

R. Marcolongo^®° treated x^-\-P=0 (mod p) in the usual manner when
explicit solutions are known. Next, from a particular set of solutions
X, y of x^+p'"?/+P = 0, where p is a prime >2, we get the solution

=i=x,=x-p'"y[ai.. .o„_i] (mod p"'+')

of Xi^-\-p"''^^yi-{-P = 0, where [ai. . .a„_i] is the numerator of next to the
last convergent to the continued fraction for p"'/{2x). The method is
Serret's, Alg. Sup^r., II. For p = 2 the results obtained are the same as in
Dirichlet's Zahlentheorie, §36.

i"Zeitschrift Math. Phys., 31, 1886, 378-80.

"SQfversigt K. Vetenskaps-Ak. Forhandlingar, Stockholm, 44, 1887, 127-153. Nova Acta

regise soc. sc. Upsalensis, (3), 12, 1884.
"»Elemente der Zahlentheorie, 1887, 182-3, 207-217. ""Giomale di Mat., 25, 1887, 161-173.

Chap. VII] BiNOMIAL CONGRUENCES. 215

F. J. Studnicka^^^ treated at length the solution in integers x, y (y<h)
of hx-{-l = y^, discussed by Leibniz in 1716.

L. Gegenbauer^^^ gave a new derivation of the equations of Berger^^^
leading to asymptotic expressions for the number of solutions of x^=Z).

A. Tonelli^^^ gave a method of solving x^=c (mod p), when p is a prime
4/i+l and some quadratic non-residue g' of p is known. Set p = 2'y-{-l,
where y is odd. By Euler's criterion, the power 72^"^ of c and g are con-
gruent to +1, —1. Set €0 = 0 or 1, according as the power 72^"^ of c is
congruent to +1 or —1. Then

For s^3, set ei = 0 or 1 according as the square root of the left member is
= -f-lor-l. Then

Proceeding similarly, we ultimately get

g2eycy=-^l (mod p), e = €o+2€i+ . . . +2'-\_2-

Thus a;= ±^'^c^^+^^/2 (mod p). Then Z^=c (mod p^) has the root

X=x^'-'c(^^-'^^"'+i^/2 (mod p^).

G. B. Mathews'^^ (p. 53) treated the cases in which x^^a (mod p) is
solvable by formulas. Cf. Legendre.-^^^

S. Dickstein^^^ noted that H. Wronski^^^ gave the solution

rM -l(7r-l)

y==hK+{-iy+'+Mi, 0 = /i+(-1)'+'A| ^, ttJ +Mj

of 2"— a?/"=0 (mod M) with (iV^)^ in place of K, and gave, as the condition
for solvability,

a(lV^)2"-l=0(modM).

But there may be solutions when the last condition is satisfied by no
integer A;. This is due to the fact that the value assigned to y imposes a
limitation, which may be avoided by using the same expressions for y, z
in a parameter K, subject to the condition aK" — 1 = 0 (mod M).

M. F. J. Mann"^'^ proved that, if n=2^XV. . ., where X, m, • • • are dis-
tinct odd primes, the number of solutions of x^= 1 (mod n) is GGiGi . . .
QiQi . . . , where G= 1 if n or p is odd, otherwise G is the g. c. d. of 2p and 2^~'^,
and where Gi, Gi,.., gi, g2,. . are the g. c. d.'s of p with X"~\ m''~\- • •>
X — l,jLi— 1,. . ., respectively.

A. Tonelli^^^ gave an explicit formula for the roots of x^=c (mod p^),

"iCasopis, Prag, 18, 1889, 97; cf. Fortschritte Math., 1889, 30.

"^Denkschriften Ak. Wiss. Wien (Math.), 57, 1890, 520.

"'Gottingen Nachrichten, 1891, 344-6.

I'^BuU. Internat. de I'Acad. Sc. de Cracovie, 1892, 372 (64-65); Berichte Krakauer Ak. Wiss.,

26, 1893, 155-9.
"^aMath. Quest. Educ. Times, 56, 1892, 24-7.
"^AttiR. Accad. Lincei, Rendiconti, (5), 1, 1892, 116-120.

216 History of the Theory of Numbers. [Chap, vii

when p is an odd prime, and a quadratic non-residue ^ of p is known.
Set p = 2'a+l, where s^ 1 and a is odd. Then y = ap^~^ is odd, and
{}>(p^) = 2'y. Tonelli's earlier work for modulus p now holds for modulus
p^ and we get x= ± g'^c^'^'^^^^. If s = 1, then e = 0 and the root is that given
by Lagrange if X = l. If s = 2, whence p = 4a+l = 8Z+5, the expression
for X is given a form free of e = cq:

x= ± (c»+3)V^+^^/^ y = ap^-\

A. Tonelli^^^ expressed the root x in a form free of e for every s:

7+1

where the v's are given by the recursion formula

v.-H = c''-S?.t^'\ . .t^--,%+k (/i = 2, 3,. . .).

Here k is an existing integer such that A;-|-l is a quadratic residue of p,
and A: — 1 a non-residue. Thus, if s = 3,

7+1

x=^{c^''+ky {{c-'+ky^C+kl^'c 2 ,

where we may take A: = —2 if a is not divisible by 3, but A; = —4 if a is divi-
sible by 3, while neither a nor 4a +1 are di\'isible by 5.

N. Amici^^ proved that a;^*=6 (mod 2"), h odd, k^v — 2, is solvable only
when h is of the form 2^'"^^/i+l and then has 2^+^ roots, as shown by use of
indices. For (x'")^ = 5, the same condition on b is necessary ; thus it remains
to solve x'"=j8 (mod 2') when m is odd. If i3 = 8A;+l or 8A:+3, it has an
index to the base 8/z + 3 and we get an unique root. If /3 = 8/j — 3 or 8A: — 1,
then x'"= — j3 has a root a by the preceding case, and —a is a root of the
proposed congruence.

Jos. Mayer^^^ found the number of roots of x^=a (mod p''), for the
primes 2, 3, p = 6m='= 1. If fli, Go,. . . are residues of nth powers modulo p,
and if g is the g. c. d. of n and p — 1, then 0102- . . = -f-l or —1 (modp),
according as p' = (p — l)/g is odd or even. If p' is even, we can pair the
numbers belonging to the exponent p' so that the sum of a pair is 0 or p;
hence there exists a residue of an nth power = — 1 (mod p) ; but none if
p' is odd.

K. Zsigmondy^^ obtained by the use of abelian groups known theorems
on the number, product and sum of the roots of x*= 1 (mod m).

G. Speckmann^^^ considered x^=a (mod p), where p is an odd prime.
Set P=(p — 1)/2. When they exist, the roots may be designated P — k,
P-\-l-\-k, whose sum is p. The successive differences of P^, (P-|-l)^
(P+2)2,. . . arep, p+2, p+4, . . .. Thesumof 2 = s+l termsof 2,4, 6, . . . is
s'^+Ss+2 = z^+z. Adding to the latter the remainder r obtained by di\'iding
P^ by p, we must get pn-{-a. Hence in pn-\-a—r we give to n the values

i»«Atti R. Accad. Lincei, Rendiconti, (5), 2, 1893, 259-265.

"'Ueber nte Potenzreate und binomische Congruenzen dritten Grades, Progr., Freising, 1895.

>»^\rcliiv Math. Phys., (2), 14, 1896. 445-8; 15, 1897, 335-6.

Chap. VII] BiNOMIAL CONGRUENCES. 217

0, 1,2,... until we reach a number of the form ^-\-z (found by extracting
the square root). Then fc = s, so that the roots P-A^, P+l+Zc are found.
N. Amici^^^ proved that if neither m nor 6 is divisible by the prime p,
and if a is a given root of x'^=h (mod p), and if /3, g are (existing) integers
such that

i3(/)(p')-p'-i + l=mg,

then of^'^"^ is a root of x™=6 (mod y^). Hence we limit attention to the
case X = l. Consider henceforth x'^=h (mod p), where p = 2''/i+l is an
odd prime, h being odd, and 6 not divisible by p. First, let ¥^8. Then
6''=1 (mod p) is a necessary and sufficient condition for solvabihty and
x= ± y^ are roots, where q is such that 2^q — 1 is divisible by /i. If gr is a
quadratic non-residue of p, all 2" roots are given by ± 6''gr''', where e = 6i+2e2
4- . . . +2*~^€^,_i, the ei taking the values 0 and 1 independently. Finally,
let A:<s. Then two roots ±(3 are determined by the method of TonelU,
while all the roots are given by

x==^^g'', t = e,+2e2+ . . . +2'-\_„ €^ = 0 or 1.

R. Alagna^°° considered a prime p = 4/c+l for which /b is a prime. Since
2 is known to be a primitive root of p, it is easy to write down those powers
of 2 which give all the roots of x'^=l (mod p), where d is one of the six
divisors 2' or 2'k of p — 1, likewise of x'^^N, since N must be congruent to
an even power of 2. For the modulus p^, we may apply the first theorem
of Amici or proceed directly. The same questions are treated for a prime
4A;+3 for which 2A; + 1 is a prime.

A. Cunningham^"^ treated at length the solution of x^=\ (mod iV'),
where iV is a prime, and gave tables showing all incongruent roots when
< = 1, 2, N-^ 101, I any admissible divisor of iV — 1 ; also for a few additional
f's when N is small.

Cunningham^oi" treated a^= 1 (mod q^) and 3.2^= ± 1 (mod p). He^oi*-
treated the problem to find 5''=+l or ±a, given a^=\, a''=^h (mod p),
where ^ is odd and ^, x, 17 are the least values of their kind; also given
a*=l, a'^^^h, a'=^c, to find the least /? and 7 such that h^=c, c^=6
(mod p).

W. H. Besant^°^ would solve y^ = ax+h by finding the roots s of s^=6
(mod a). Then y = ar-\-s, x = ar^-\-2rs+{s'^ — h)/a.

G. Speckmann^°^ replaced x"=A; (mod p) by the pair of congruences
x"~^=r, xr^A; (mod p). In np+/c give to n the values 0, 1, 2, . . . until we
find one for which np+k = rx such that, by trial, x"~^=r. The method is, of
course, impractical.

"'Rendiconti Circolo Mat. di Palermo, 11, 1897, 43-57.

""Rendiconti Circolo Mat. di Palermo, 13, 1899, 99-129.

"^Messenger of Math., 29, 1899-1900, 145-179. Errata, Cunmngham226, p. 155. See 13a of

Ch. IV.
"i^Math. Quest. Educ. Times, 71, 1899, 43-4; 75, 1901, 52-4.
2"&/6td., (2), 1, 1902, 70-2.
^o^Math. Gazette, 1, 1900, 130.
'"'Archiv Math. Phys., (2), 17, 1900, 110-2, 120-1.

218 History of the Theory of Numbers. [Chap, vii

G. Picou^*^ applied to the case n = 2 Wronski's^^^ formula for the resi-
dues of 71 th powers modulo M, M arbitrary. For example, if M = \Qa^\,

(h=^Sa)-^ =pa{^h-iy (mod M).

[If 8a were replaced by 4a, we would have an identity in h.]

P. Bachmann^^ (pp. 344-351) discussed x"'=a (mod p"), p>2, p = 2.

G. Arnoux-°^ solved x^^=79 (mod 3-5-7) by getting the residue 2 of 79
modulo 7 and that of 14 modulo 0(7) =6 and solving x'^=2 (mod 7) by use
of a table of residues of powers modulo 7. Similarly for moduli 3, 5. Take
the product of the roots as usual.

M. Cipolla-"'^ generahzed the results of Alagna-*^" to the case of a prime
p = 2"'q-\-l, 7n>0, q an odd prime, including unity. For any divisor d of
p — 1, the roots of x'^=N (mod p) are expressed as given powers of a primi-
tive root a of p. If 2 belongs to the exponent 2''co modulo p, where w is
odd, theng'= 1 (mod p) if and only if 2""^ is the highest power of 2 dividing m.

Cunningham-"^" found the sum of the roots of (i/"=tl)/(?/±l) = 0
(mod p).

M. Cipolla'"^ proved the existence of an integer k such that k~ — q is a
quadi'atic non-residue of the prime p not dividing the given integer q. Let

Un = h^q\{kWqr-{k-Vqr\,

v^=Viik+V¥^r+{k-V¥^r\.

By expansion of the binomials it is shown that the roots of x^=q (mod p)
are given by =*=W(p_i)/2 and by ±y(p+i)/2. These may be computed by use of

Wn=2kWn_i—qWn-2 (mod p) {w = u or v),

with the initial values Uq = 1, Wi = p; ^0 = 1? Vi = k. Although u^, y„ are the
functions of Lucas, the exposition is here simple and independent of the
theory of Lucas (Ch. XVII).

M. Cipolla-°^ proved that if 5 is a quadratic residue and k^—q is a
quadratic non-residue of an odd prime p, z~^q (mod p^) has the roots

^lVq\{k+Vqr-{k-V~qr\,
where r = p^~\p — 1)/2. Other expressions for the roots are

^hq'{(k+V¥^r+{k-V¥^y\,

t=ip^-2p^-' + l)/2, s = p^-\p + l)/2.

Thus if Zi~=q (mod p), the roots modulo p^ are ^q'zi^^''^ (TonelH^^^).
Finally, let n=TLpi^', where the p's are primes >3; take e, = =»=l when
Pi=^l (mod 4). There exists a number A of the form k^—q such that

^ML'iatermddiaire dea math., 8, 1901, 162.

'^o* Assoc, frang. av. sc, 31, 1902, II, 185-201.

»«Periodico di Mat., 18, 1903, 330-5.

»'»«Math. Quest. Educ. Times, (2), 4, 1903, 115-6; 5, 1904, 80-1.

"'Rendiconto Accad. Sc. Fis. e Mat. Napoli, (3), 9, 1903, 154-163.

"8/6id., (3), 10, 1904, 144-150.

I

Chap. VII] BiNOMIAL CONGRUENCES. 219

(A/pi) = €i,. . ., (A/pJ = e^, where the symbols are Legendre's. Call M
the 1. c. m. of pl^~\pi — ei)/2 for {=1,..., v. Then z^=q (mod n) has
the root

A. Cunningham^°^ indicated how his tables may be used to solve
directly x''= —1 (mod p) for n = 2, 3, 4, 6, 12. From p = a^-\-h^, we get the
roots re = ± a/6 of a;^=— 1 (modp). Also p = a^+ 6^ = c^+2(i^ gives the roots
=i= d{a-\-b) / (ce) and ±c(a±6)/(2de) of x^^—1 (mod p), where e = a or 6.
Again, p = A^+SB^ gives the roots iA-B)/{2B), {B+A)/{B-A), and
their reciprocals, of x^=l (mod p).

M. Cipolla^°^ gave a report (in Peano's symbolism) on binomial con-
gruences.

M. Cipolla^^° proved that if p is an odd prime not dividing q and if
z^=q (mod p) is solvable, the roots are

z= ^2{qs,+q\+q\+ . . . +5'^~'%-4+Sp-2)
where

s,=r+z+...+

m-

Then x^=q (mod p'^) has the root z^^ V, e = (p^-2p^-^ + l)/2. For p=l
(mod 4), x'^=q (mod p) has the root

4 1 5^S2,_i- 2 q^-%j_s+2 S g^s^^.i (z = ^) •

1=1 y=i i=l \ 1 /

M. Cipolla^^^ extended the method of Legendre^^® and proved that

x^"'=l-\-TA (mod 2*),
for A odd and s^w+2, has a root

x = l+2^Aci-22M2^2+- • • + (-l)"'"'2"^A"c„, n=r _^~^ J,

where ^_]_ ^(2'"-l)(2-2'"-l) . . .(n^l-2'"-l)

are the coefficients in

il+zy^'"' = l+c,z-c,z'+c,z'- . . . -(-1)X2"+. . ..
0. Meissner^^^ gave for a prime p = Sn+5 the known root

£+3 £-1

^ = D » oix^=D (modp), D * =i (modp).

But if 2)^p-i)/4= _i (mod p), a root is ^](p — 1)/2)!, since the square of the
last factor is congruent to ( — l)(p+^)/2 j-^y wrjigon's theorem.

Tamarkine and Friedmann^^^ expressed the roots of z^^q (mod p) by a
formula, equivalent to Cipolla's,^^°

^osQuadratic Partitions, 1904, Introd., xvi-xvii. Math. Quest. Educ. Times, 6, 1904, 84-5; 7,

1905, 38-9; 8, 1905, 18-9.
""Rendiconto Accad. Sc. Fis. e Mat. Napoli, (3), 11, 1905, 13-19.
"i/6id., 304-9.

'"Archiv Math. Phys. (3), 9, 1905, 96.
2"Math. Annalen, 62, 1906, 409.

220 History of the Theory of Numbers. [Chap, vii

(p-3)/2

z==b2 2 q^''-''-"'s2^+,.

m = 0

For, according as 2/^ is or is not =q (mod p), we have

y\i-{y^-qy~'\=y or o (mod p).

We can express S2m+\ in terms of Bemoullian numbers.

A. Cunningham-^^ gave a tentative method of solving x'^=a (mod p).
He-^^^" noted that a root Y=2r]^ of Y^=-l leads to the roots of y^=-l
(mod p).

M. Cipolla^^^ employed an odd prime p and a divisor n of p — l=ni/.
If Ti, . . ., r, form a set of residues of p whose nth powers are incongruent,
and if ^'=1 (mod p), then x''=q (mod p) has the root

k=0 ;=1

Forn = 2, this becomes his^^° earUer formula by taking 1,2,..., (p — 1)/2 as
the r's. Next, let p — l=mji, where m and /x are relatively prime and m
is a multiple of n. If 7 and 8 belong to the exponents m and /x modulo p,
the products 7''5* {r<m/n, s<iJi) may be taken as ri,. . ., r,. According as
nk= 1 or not (mod /x), we have

y{nk-l)m/n -j^

At= -ufi — „^_i - or Ak=0 (mod p).
7 — i

If n is a prime and n" is its highest power dividing p — 1, there exists a
number co not an nth power modulo p and we may set m = n'', 7=0)" (mod p).
In particular, if n = 2, x^^q has the root

_ 1 P+2^-1 2'"-'-l

2 «=o

where co is a quadratic non-residue of p. If p=5 (mod 8), we may take
CO = 2 and get

M. CipoUa^^® considered the congruence, with p an odd prime,

x^ =a (mod p"*), r<7n,

a necessary condition for which is that h = {a^ — a)/p'"^' be an integer.
Determine A by a^ A=h (mod p"*). Then the given congruence has the
root axo if Xq is a root of

:r'''=l-^p'+' (modp"*).
This is proved to have the root

'"Math. Quest. Educ. Times, (2), 13, 1908, 19-20.

^^"^Ibid., 10, 1906, 52-3.

"»Math. Annalen, 63, 1907, 54-61.

>"Atti R. Accad. Lincei, Rendiconti, (5), 16, I, 1907, 603-8.

Chap. VII] BiNOMIAL CONGRUENCES. 221

where Ci = l/p*", . . . are given by the expansion

^1—2 ==l—CiZ — C2^ —

M. Cipolla^" treated x"=a (mod p"*) where n divides 4>{p^). We may
set n = p'v, where v divides p — 1. Determine integers a, j3 such that

Then the initial congruence has the root yx^" if y^^=a^ (mod p"*), solved as
in his preceding paper, and if Xi is a root of x''=a (mod p"*). The latter
has the root

^ A;=0 t = l

where t={p — l)/v, pi^rf""' (mod p'"), ri, . . ., r^ being integers prime to p
such that their j/th powers are incongruent and form a group modulo p"*.

K. A. Posse^^^ gave a simplified exposition of Korkine's^^^ method of
solving binomial congruences. Cf. Posse/^^ Schuh.^^^'^

F. Stasi^^^ proved that we obtain all solutions of x^=a^ (mod n), where
n is odd and prime to a, by expressing n as a product of two relatively
prime factors P and Q in all ways, setting x — a = Pz and finding z from
Pz+2a=0 (mod Q). [Instead of his very long proof, it may be shown at
once that we may take x — a, x+a divisible by P, Q, respectively.]

L. Grosschmid^^° gave for the incongruent roots of x^^r (mod M) an
expHcit formula obtained by means of the ideal factors of ilf in a quadratic
number-field.

L. Grosschmid^^^ treated the roots of quadratic binomial congruences.

A. Cunningham^^^ solved x^= —1 (mod p), where p = 616318177 is a prime
factor of 2^^ — 1; by using various small moduli, he obtained p = 24561^ +
36161

L. von Schrutka^^^'' used a correspondence between the integers and
certain rational numbers to treat quadratic congruences without novelty as
to results. The method will be given under the topic Fields in a later
volume of this History.

Grosschmid^^^ employed the products R and N of all the quadratic
residues and non-residues, respectively, ^2n of a prime p = 4n+l. Then

R^={-iy+\ iv2=(_i)« (modp).

2"Atti R. Accad. Lincei, Rendiconti, (5), 16, I, 1907, 732-741.

"'Charlkov Soobsc. Mat. Obs6 (Report Math.Soc. Charkov), (2), 11, 1910, 249-268 (Russian).

"»I1 BoU. Matematica Gior. Sc.-Didat., 9, 1910, 296-300.

«20Jour. fur Math., 139, 1911, 101-5.

""Math. 6s Phys. Lapok, Budapest, 20, 1911, 47-72 (Hungarian).

222Math. Questions Educat. Times, (2), 20, 1911, 33-4 (76).

2««Monatshefte Math. Phys., 23, 1912, 92-105.

223Archiv Math. Phys., (3), 21, 1913, 363; 23, 1914-5, 187-8.

222 History of the Theory of Numbers. [Chap, vii

Hence ±7? and =»=iV are the roots of x^=— 1 (mod p) according as
p = S7n + l or Sm + 5. ,;,

U. Concina"^ proved the first result by Legendre.^^

A. Cunningham--^ tabulated the roots of i/*=±2, 2?/"*=±l (mod p),
for each prime p< 1000.

Cunningham"^ listed the roots of ?/'= ± 1 (mod p"), where l^qp",
p being an odd prime ^19, p''<10^, a = l and often also a = 2, q a factor
of p— 1.

A. Gcrardin and L. Valroff"7 solved 2i/=l (mod p), 1000<p<5300.

Cunningham-^^ announced the completion of tables giving all proper
roots of ?/'"= 1 (mod p*) for m odd ^15, and of 'y'"= — 1 (mod p*) for m even
^ 14. These tables have since been completed up to p* < 100000 and are
now nearly all in type.

T. G. Creak^-^ announced the completion of like tables for m = 16 to
50; 52, 54, 56, 63, 64, 72, 75, and 10^<p'^<10^

H. C. Pocklington--^ noted that if p is a prime 8m+5 and a}"'^^=-l,
x^=a (mod p) has the roots =»=^(4a)'"'^^ He showed how to use {t-\-
u\/DY to solve a;-= —D (mod p=4A-+l), and treated a:^=a.

*J. Maximoff^^° treated binomial congruences and primitive roots.

*G. Rados-^^ gave a new proof of known criteria for the solvability of
x- = D (mod p). He-^^ gave a new exposition of the theory of binomial
congruences without using indices.

Congruences ^''"^^l (mod p") are treated in Chapter IV. Euler**''
of Ch. XVI solved x-=— 1 (mod p). Lazzarini"^ of Ch. I erred on the
number of roots of 2-= —3 (mod n). Many papers in Ch. XX treat x*=a;
(mod 10"). The following papers from the first part of Ch. VII treat also
binomial congruences: Euler,^ Lagrange,^ Poinsot," Cauchy,^^ Lebesgue,"
Epstein,i^2 Korkine."^

=«*Periodico di Mat., 28, 1913, 212-6.
22*Messenger Math., 43, 1913-4, 52-3.
2"/Wd., 148-163. Cf. Cunningham .201
227Sphinx-0edipe, 1913, 34; 1914, 18-37, 73.
228Messenger Math., 45, 1915-6, 69.
2^Proc. Cambridge Phil. Soc, 19, 1917, 57-9.
2^Bull. Soc. Phys.-Math. Kasan, (2), XXI.
23iMath. 4s Term^s Ertesito, 33, 1915, 758-62.
^Ibid., 34, 1916, 641-55.

CHAPTER VIII.

HIGHER CONGRUENCES.

A Congruence of Degree n has at most n Roots if the
Modulus p is a Prime.

J. L. Lagrange^ proved that, if a is not divisible by the prime p, ax'^+fex""^
+ . . . is divisible by p for at most n integers x between p/2 and — p/2.
For, let a, jS, . . . , p, (7 be n+1 such distinct integers. Then the quotient of

a(a:'^-a")+6(a:'^-i-a"-^)+ . . .

by a: — a is a polynomial aa:"~^ + . . . which is divisible by p when x=^,. . .,a.
Proceeding as before, we finally have a{p—<7) divisible by p, which is
impossible.

L. Euler^ noted that a:" — 1 is divisible by a prime p for not more than n
integers x, 0<x<p. For, if x = a, is such an integer, then x — a divides
x^ — l—mp, where m is a suitable integer; the quotient / is of degree n — 1.
If a: = 6 is a second such integer, x — h divides/— m'p. Proceeding as in alge-
bra, we obtain the theorem stated. [The argument is applicable to any
polynomial of degree n in x.]

A. M. Legendre^ noted that P^(x — a)Q-\-pA has only one more root
than Q.

C. F. Gauss'* proved the theorem by assuming that there is a congruence
ox"4- . . . = 0 (mod p) with more than n roots a, . . ., and that every con-
gruence of degree I, Kn, has at most I roots. Substituting y+a for x, we
obtain a congruence a?/"-f- ... =0 with more than n roots, one of which is
zero. Removing the factor y, we obtain a?/"~^+. . . = 0 with more than
w — 1 roots, contrary to hypothesis.

Gauss^ noted that if a is a root of ^=0 (mod p), then ^ is divisible by
x — a modulo p. li a, b,. . . are incongruent roots, ^ is divisible modulo p
by the product (x — a){x — b).... Hence the number of roots does not
exceed the degree of ^.

A. Cauchy^ made the proof by use of X=(x — a)Xi (mod p), identically
in x, where the degree of Xi is one less than the degree of X.

A. L. Crelle^ and S. Earnshaw^ gave Lagrange's proof.

Crelle^ proved that if ei, . . ., e„ are n distinct roots, '

ax^^-i- . . . = a(x — ei) . . .{x — e^+pN.

iMem. Ac. BerUn, 24, ann6e 1768 (1770), p. 192; Oeuvres, 2, 1868, 667-9.

='Novi Comm. Ac. Petrop., 18, 1773, p. 93; Comm. Arith., 1, 519-20.

»M^m. Ac. Roy. Sc, Paris, 1785, 466; TWorie des nombres, 1798, 184.

♦Disq. Arith., 1801, Art. 43.

^Posthumous paper, Werke, 2, p. 217, Art. 338 (p. 214, Art. 333). Maser's German translation

of Gauss' Disq. Arith., etc., 1889, p. 607 (p. 604).
"Exercices de Math., 4, 1829, 219; Oeuvres, (2), 9, 261; Comptes Rendus Paris, 12, 1841,

831-2; Exercices d'Analyse et de Phys. Math., 2, 1841, 1-40, Oeuvres, (2), 12.
'BerUn Abhand., Math., 1832, p. 34.
Cambridge Math. Jour., 2, 1841, 79.
•BerUn Abhand., Math., 1843, 50-54.

223

224 History of the Theory of Numbers. [Chap.viii

'J
L. Poinsot^" gave the proof due to Crelle.' ■

J. A. Gninert^^ proceeded by induction from n — 1 to n, making use of

the first part of Lagrange's proof.
D. A. da Silva^' gave a proof.

Number of Roots of Higher Congruences.

G. Libri^" found that /(a:, ?/, . . .) = 0 (mod m) has

I

1 b d

-22

Wl x=o v=t

;--! 2A-7rf . . 2Uj\

.ALi COS \-x sm \

Lfc=o Tnn m \

sets of solutions such that a^x^6, c^?/^d, .... The total number of
sets of solutions is

1 ^ ^ r, , 27r/, 47r/ , , Am-X)'KJ\

— 2 2 . . . O +COS — ^+cos — ^+ . . . +COS 2^^ '-^ V

7^1=0 v=o y m m m \

V. A. Lebesgue^^ proved that if p is a prime we obtain as follows the
residue modulo p of the number S>k of sets of solutions of F{xx, . . ., x„) = 0
(mod p), in which each x, is chosen from 0, 1,. . ., p — 1, and F is a poly-
nomial with integral coefficients. Let 2A be the sum of the coefficients of
the terms Ax^ ■ ■ x/ of the expansion of F^~'^ in wliich each of the exponents
a, . . . , ^ is a multiple > 0 of p - 1 . Then Sk= ( - 1) *"^^ 2 A (mod p) .

Henceforth, let p = hm+l. First, let F = x"'—a. In F^~^ the coefficient
of a;""'?-!-"^ is (p-^)(-a)"=a" (mod p). The exponent of x will be a multiple
>0 of p — 1 only when n = k(p — l)/d, for A: = 0, 1,. . ., d — 1, where c? is the
g. c. d. of m and p-L Thus 51=20*^^"^^'''^ (mod p), while evidently Si<p.
According as a'-^~^^^'^=l or not, we get Si=d or 0.

Next, let F = x"'-ay"'-h. Set c = ay"'-\-h. In (x"'-c)p-^ we omit the
terms in which the exponent of x is not a multiple >0 of p — 1 and also the
^rn(p-i) jjq|. containing y. Since the arithmetical coefficient is =1 as in the
first case, we get

In this, we replace c'''' by those terms of (ay"* +6)'''' in which the exponents
are multiples >0 of p — 1, viz.,

SGB^"^")

kh-lhUh

Set 2/ = 1, and sum for A* = 1, . . . , w — 1 ; we get —S2 (mod p). It is shown
otherwise that *S2 is a multiple <mp of m.

To these two cases is reduced the solution of

(1) ^ = 01X1"*+. . .-\-a^k"=a (mod p = hm-\-l).

"Jour, de Math^matiques, 10, 1845, 12-15.

"Klugel'8 Math. Worterbuch, 5, 1831, 1069-71.

"Proprietades . . .Congruencias binomias, Lisbon, 1854. Cf. C. Alasia, Rivista di fisica, mat.

e sc. nat., 4, 1903, p. 9.
"Mdm. divers Savants Ac. Sc. de I'Institut de France (Math.), 5, 1838, 32 (read 1825). Jour.

fur Math., 9, 1832, 54. To be considered in vol. n.
"Jour, de Math., 2, 1837, 253-292. Cf. vol. 3, 113; vol. 4, 366.

Chap. VIII] NuMBER OF RoOTS OF CONGRUENCES. 225

Denote by P the sum of the first / terms of F and by Q the sum of the last
k—f terms. Let gr be a primitive root of p. Let P° be the number of sets
of solutions of P=0 (mod p); P^'^ the number for P^g^ (mod p); Q^ and
Q^'^ the corresponding numbers for Q=0, Q=g'. Then the number of
sets of solution of P=Q (mod p) is P°Q°+/iS:=rP^*^Q^*\ Hence we may
deduce the number of sets of solutions of P=0 from the numbers for
P = Aand Q= -A. For P= a, we employ P = P, Q = /x'"and get P° = P°
-\-{'p — l)P^^\ which determines the desired P''^\

The theory is applied in detail to (1) for m = 2, k arbitrary, and for
w = 3, 4, k = 2. Finally, the method of Libri^^ is amplified.

Th. Schonemann^^ noted that, if Sk is the sum of the A;th powers of the
roots of an equation x"+ . . . =0 with integral coefficients, that of x"" being
unity, and if >S(p_i)«=n (mod p) for <= 1, 2, . . ., w, where p is a prime >n,
the corresponding congruence a;"+ . . . = 0 (mod p) has n real roots.

A. L. Cauchy^^ considered F{x) = Q (mod M), with M=AB. . ., where
A, B,. . . are powers of distinct primes. If F{x) = 0 (mod A) has a roots,
F(x) = 0 (mod B) has /S roots, etc., the proposed congruence has a/3. . . roots
in all. For, if a, 6, . . . are roots for the moduli A, B,. . . and X=a (mod A),
X=b (mod P), . . . , then X is a root for modulus M.

P. L. Tchebychef^° proved that, if p is a prime, a congruence /(x)=0
(mod p) of degree m<p has m roots if and only if the coefficients of the
remainder obtained by dividing x^—x hj f{x) are all divisible by p.

Ch. Hermite^^ proved the theorem: If fx and jjl' are the numbers of
sets of solutions of 4>{x, y)=0 for the respective moduli M and M', which
are relatively prime, the number of sets of solutions modulo MM' is /jl/j,'.
If 0=0 is solvable for a prime modulus p, it will be solvable modulo p" if

have no common sets of solutions. In this case, the number of sets of
solutions modulo p" is p"~V if tt is the number for modulus p. Similar
results are said to hold for any number k of unknowns. If ikf is a product
of powers of the distinct primes pi, . . ., p„, and if tt, is the number of sets
of solutions of the congruence modulo Pi, then the number of sets for
modulus M is

M'

k~l TTi-.-TTn

For a:^+A|/^=A (mod M), we have Xj = p, — (— A/p»), where (a/p) is
=«= 1 according as a is a quadratic residue or non-residue of p.

JuUus Konig gave a theorem in a seminar at the Technische Hochschule
in Budapest during the winter, 1881-2, which was published in the following
paper and that by Rados.^^

"Jour, fiir Math., 19, 1839, 293.

"Comptes Rendus Paris, 25, 1847, 36; Oeuvres, (1), 10, 324.
"Theorie der Congruenzen, in Russian, 1849; in German, 1889, §21.
"Jour, fiir Math., 47, 1854, 351-7; Oeuvres, 1, 243-250.

226 History of the Theory of Numbers. [Chap, viii

G. Raussnitz*^ proved the theorem, due to Konig: Let
(2) f{x) =aoX^-2+OiX''-H . . . +ap_2,

where the a's are integers and ap_2 is not divisible by the prime p. Then
f{x)=0 (mod p) has real roots if and only if the cyclic determinant

(3) D =

Oo Oi 02 ... ap_3 ap_2
«! a2 03 ... ap_2 Oo

Op_20o Oi ... Op_4 Op.s

is divisible by p. In order that it have at least k distinct real roots it is
necessary that all p — k rowed minors of D be divisible by p. If also not
all p — k — 1 rowed minors are divisible by p, the congruence has exactly
k distinct real roots.

The theorem is applicable to any congruence not ha\'ing the root zero,
since we may then reduce the degree to p — 2 by Fermat's theorem.

Gustav Rados-'* proved Konig's theorem, using the fact that a system of
p — l linear homogeneous congruences modulo p in p — 1 unknowns has at
least k sets of solutions linearly independent modulo p if and only if the
p — k rowed minors are divisible by p.

L. Kronecker^^ noted that, if p is a prime, the condition for the existence
of exactly p—m — 1 roots of (2), distinct from one another and from zero,
is that the rank of the system

(3') (a,+,) (i,A: = 0, l,...,p-2)

modulo p is exactly m, where Os+p_i = a^. The same is the condition for
the existence of a {p—m — l)-fold manifold of sets of solutions of the system
of linear congruences

2'a,+,0,= 0 (mod p) ( A = 0, 1 , . . . , p - 2) .

fc=0

L. Kronecker^^ gave a detailed proof of his preceding results, noted that
the rank is ?« if not all principal t?? -rowed minors are divisible by p while
all VI -{-1 rowed minors are, and added that Co+Ci.t+ . . . +Cp_2a:^~^=0
(mod p) has exactly s roots 7^0 if one and the same linear homogeneous
congruence holds between every set of p—s (but not fewer) successive
terms of the periodic series Cq, Ci, . . . , Cp_2, Cq, Ci, . . . .

L. Gegenbauer^^ proved Kronecker's version of Konig's theorem.

Gegenbauer^^ noted that Kronecker's theorems imply the corollary:

"Math, und Naturw. Berichte aus Ungam, 1, 1882-3, 266-75.

"Jour, fiir Math., 99, 1886, 258-60; Math. Termea Ertesito, Magj'ar Tudon Ak., Budapest, 1,

1883, 296; 3, 1885, 178.
»Jour. fur Math., 99, 1886, 363, 366.
**Vorlesungen liber Zahlentheorie, 1, 1901, 389-415, including several additions by Hensel

(pp. 393, 399, 402-3).
"Sitzungsber. Ak. Wiss. Wien (Math.), 95, II, 1887, 165-9, 610-2.
*^Ibid., 98, Ila, 1889, p. 32, foot-note. Cf. Gegenbauer.«

Chap. VIII] NuMBER OF RoOTS OF CONGRUENCES. 227

There exist exactly p—m—2 roots of (2), distinct from one another and
from zero, if and only if there exist exactly p — m — 2 distinct linear homo-
geneous functions

p-2

Xak,hah {k = l,. . .,p-m-2)

h=0

which remain divisible by p after applying all cyclic permutations of the
ah, so that

sV»a,„^0 (mod p) filo/iV.'.^.T™-!)-

A simple proof of this corollary is given.

L. Gegenbauer^^ noted that the niunber of roots of /(a^)=0 (mod k) is

since D{k) = 1 or 0 according as /(a:) is divisible by k or not. Let ki,...,ka
be a series of increasing positive integers and g{x) any function. In the
first equation take k = ki, multiply by g{ki) and sum iorl = l,. . .,8. Revers-
ing the order of the summation indices I, x in the new right-hand member,
we get

i \f(x), h\g{k) = S G, G=XD{ix)g{f,),

1=1 1=0

where in G the summation index n takes those of the values ki,...,ki which
exceed x. Thus G represents the sum G{f{x)] ki,..., k^; x) of the values
oi fifx) when ij, ranges over those of the numbers ki,. . ., ks which exceed x
and are divisors oif{x). In particular, if ^(x) = 1, G becomes the number x}/
of the k's which exceed x and divide /(a:).

Let f{x)=vi^nx. Then f{x) = 0 (mod k) has {k, n) roots or no root
according as m is or is not divisible by the g. c. d. {k, n) of k and n; let
{k, 71] m) denote {k, n) or 0 in the respective cases. Then

S {ki, n; m) g{ki) = s G(m^nx; ki,. . ., k^; x).

'-1 x=0

Let G{a, h) denote the sum of the values of g(ii) when n ranges over all
the divisors >6 of a; xl/{a, h) the number of divisors >b of a. Taking
ki = l ioT 1=1,. . ., d, we deduce

S 5-1

S (Z, n; m)^(0= S {G{m^nx, x)-G{m^nx, b)\.

1=1 z=0

For gil) = 1, this reduces to Lerch's^°° relation (16) in Ch. X. Again,

a b

2 {G{m+nx, x — 1) —Gim+nx,h+x)\ = S {G{m—nfx,tx) — Giin—nfx,ti-\-a)\,

X-l u=0

"SitzuDgsberichte Ak. Wiss. Wien (Math.), 98, Ila, 1889, 28-36.

228 History of the Theory of Numbers. [Chap, viii

which for g{x) = l yields the first formula of Lerch. Next, if the A;'s are
primes and g is a prime distinct from them,

2 Gix'^-q] k,,.. ., k,; x)= 2 (fc,-l, n; q)g{ki).

x=0 /=1

Finally, he treated f{x) of degree d = A-j — 2, whose constant term is prime to
each A-, and coefficient of x''~' is divisible by the prime k^ if i<ks — k^.

Gegenbauer^" noted that, if p — l—n is the rank of the system (3)
modulo p, the congruence, satisfied by the distinct roots 5^0 of (2) and by
these only, is given symboUcally by

(-X--V

\dai daj

fli+fc I =0 (mod p) {%, k = 0,. . ., p-2).

He obtained easily Kronecker's"^ form of the last congruence. He gave
necessary and sufficient conditions, expressed in terms of a comphcated
determinant and its /z — l successive derivatives with respect to Op_2, in
order that (2) and a second congruence of degree p — 2 shall have jx common
roots ?^0, and found the congruence satisfied by these ji common roots.
He deduced determinantal expressions for the sum o-^ of the rth powers of
the roots of (2), and for the coefficients in terms of the cr's.

Michael Demeczky^^ would employ Euclid's process to find the g. c. d.
G{x) modulo p of (2) and x'^—x. If G{x) = 0 (mod p) is of degree v it has
V real roots and these give all the real roots of (2) . Multiple roots are then
treated. The case of any composite modulus is known to reduce to the
case of p', p a prime. If (2) has X distinct real roots, not multiple roots, we
can derive X real roots of /(a;) = 0 (mod p'). If pi, . . . , p„ are distinct primes
and if /(x) = 0 (mod p,) has X, real roots, then/(x) = 0 (mod pi. . .p„) has
Xi. . .X„ real roots, and is satisfied by every integer x if the former are.
Various sets of necessary and sufficient conditions are found that f{x) = 0
(mod m=np'<) shall have m distinct real roots; one set is that/(x)=0
(mod p'<) identically for each i.

L. Gegenbauer^^ proved that a congruence modulo p, a prime, of degree
p — 2 in each of n variables has a set of solutions each ^0 if and only if p
divides the determinant of a cycUc matrix

A« A' ..

A'-

-1 '

A"--

-2

A^

A' A^ ..

where A" is itself a cyclic matrix in B^,. . ., B'^~^; etc., until we reach
matrices in the coefficients of the congruence. An upper limit is found for

'"Sitzungsber. Ak. Wiss. Wien (Math.), 98, Ila, 1889, 652-72.

"Math. u. Naturw. Berichte aus Ungarn, 8, 1889-90, 50-59. Math. 68 Term^s Ertesito, 7,

1889, 131-8.
»=Sitzungsber. Ak. Wiss. Wien (Math.), 99, Ila, 1890, 799-813.

Chap. VIII] NUMBER OF RoOTS OF CONGRUENCES. 229

the number of sets of solutions each not divisible by p. He proved that

s EzlL n

S ttjXj ^ + S a,+jX,+j-{-h=0 (mod p)
y=i i=i

has p""^*"^ sets of solutions. Of these,

have each x^^O, where r is the number of the 2' integers

6 =1=01 ±02='= ...=*= a,
which are divisible by p. The number of sets of solutions of

s Pui n

l^QjXj 2 +i:a,+jXs+j+b=0 (modp)

i=i 3=1

is expressed in terms of the functions used for quadratic congruences.

*E. Snopek^^ gave a generalization of Konig's criterion for the solva-
bility of a congruence modulo p.

L. Gegenbauer^^ proved that if the p congruences

S Zk^x^-^-'=0 (mod p) (X = 0, 1,. . ., p-1)

A: = 0

have in common at least p—p distinct roots not divisible by p then all
p-rowed determinants in the matrix (^^^x) are divisible by p. The converse
is proved when a certain condition holds. By specialization, Konig's
theorem is obtained.

Gegenbauer^^ proved that, if r is less than the prime p and ii Zq,. . ., 2r_i
are incongruent and not divisible by p, the system of linear congruences

(4) s' h+,y,^0 (mod p) (p = 0, 1,. . ., p-2)
has all its sets of solutions of the form

(5) 2/*^'sa,2,* (A: = 0, l,...,p-2)

x=o

or not, according as the matrix (bk+p), k = r, r+1, . . ., p — 2; p = 0, . . ., p — 2,
has a p— r — 1 rowed determinant prime to p or not. Next, if

(6) S 6;fcX^=0 (mod p)

A:=0

has exactly r distinct roots Zq, . . ., z^-i each not divisible by p, every sys-
tem of solutions of (4) is given by (5), and conversely. By combining this
theorem of Kronecker's with the former, we obtain Kronecker's form of
Konig's theorem.

"Prace Mat. Fiz., Warsaw, 4, 1893, 63-70 (in PoUsh).
'^Sitzungsber. Ak. Wiss. Wien (Math.), 102, Ila, 1893, 549-64.
"Monatshefte Math. Phys., 5, 1894, 230-2. Cf. Gegenbauer."

230 History of the Theory of Numbers. [Chap, viii

K. Zsigmondy^^ proved that, if p is a prime, there are exactly

,K«, k) = p- - Q p-' + g) p'-' -...+(- 1)» g)

congruences x"+ . . . = 0 (mod p) not having as roots k given distinct num-
bers. Also,

^(n, k)=p4^(n-l, k) + {-ir(^^, rPin, k + l)=^|^{n, A:)-^(n-l, k).

If n'^k, \J/{n, ^)=p"~''(p — 1)^'. For n = k, \p{n, k) is the number \J/{n) of
congruences of degree n with no root. The number with exactly i roots is
{'])\l/{n — i). There are {^V)\l/ii—r) distinct matrices (3) of rank i such
that Qr-i is the first one of Qq, ai,. . . not divisible by p.

K. Zsigmondy^^ considered a function $(/) of a polynomial f{x) such
that $ is unaltered when the coefficients of f{x) are increased by integral
multiples of the prime p. Let/t^'^(x), i = l,. . ., p'', denote the polynomials
of degree k which are distinct modulo p and have unity as the coefficient
of x''. It is stated that

p" p-

r,n-2

i, i' J = 1

where a takes those values 1, 2, . . ., p" for which /°^(x)=0 (mod p) does
not have as a root one of the given incongruent numbers ai, . . ., a/, while,
in the outer sums on the right, i, i',. . . range over the combinations of
1, . . ., s without repetitions.

Zsigmondy^^ had earlier given the preceding formula for the case in
which tti,. . ., a, denote 0, 1,. . ., p — \. Then taking <I>(/) = 1, we get the
number of congruences of degree n with no root (Zsigmondy^^) . Taking
$(/) =/, we see that the sum of the congruences of degree n with no root is
= 0 (mod p), aside from specified exceptions. Taking $(/)=co-^, where co
is a pth root of unity, and n^p, we see that the system /j;^(x) takes each
of the values 1, . . . , p — 1 (mod p) equally often.

Zsigmondy^^ proved his^^'^^ earher formulas, obtained for an integral
value of X the number of complete sets of residues modulo p into which
fall the values of the fH (^) not having prescribed roots, and investigated
the system 5„ of the least positive residues modulo p of the left members
of all congruences of degree n having no root. In particular, he found how
often the system B^ contains each residue, or non-residue, of a gth power.
He investigated (pp. 19-36) the number of polynomials in x which take k
prescribed residues modulo p for k given values of x.

3«Sitzung8ber. Ak. Wiss. Wien (Math.), 103, Ila, 1894, 135-144.
»'Monatshefte Math. Phys., 7, 1896, 192-3.
"Jahresbericht d. Deutschen Math. Verein., 4, 1894-5, 109-111.
"Monatshefte Math. Phys., 8, 1897, 1-42.

Chap. VIIIJ NuMBER OF RoOTS OF CONGRUENCES. 231

L. Gegenbauer'*" proved that (2) has as a root a quadratic residue or
non-residue of the prime p if and only if the respective determinant

P = \ a^+i+o^+i+x \, N = \ a^+i-a^+i+, \ (i, /i = 0, . . ., tt-I)

be divisible by p, where 7r= (p — 1)/2. From this it is proved that (2) has
exactly ir—r distinct quadratic residues (or non-residues) of p as roots if
and only if P (or N) and its tt — 1— r successive derivatives with respect to
a,_i+ap_2 have the factor p, while the derivative of order tt— r is prime
to p. These residues satisfy the congruence

where K = P or N, while the j^th power of the sign of differentiation repre-
sents the ^'th derivative. A second set of conditions is obtained. Con-
gruence (2) has exactly tt — I—k distinct quadratic residues as roots if and
only if the determinants of type P with now i = 0, . . ., k, k+1 and fi = 0,. . . ,
K, T, are divisible by p for r = /c+l, . . ., tt — 1; while p is not a factor of the
determinant of type P with now i, fx = 0,. . ., k. These residues are the

roots of

«■

S I a^+i+a^+i+^ I x'~^~^=0 (mod p),

T=(C

where ^ = 0, . . ., k, and /x = 0, . . ., k — 1, t in the determinants. For non-
residues We have only to use the differences of a's in place of sums.

S. O. Satunovskij^^ noted that, for a prime modulus p, a congruence of
degree n (n<p) has n distinct roots if and only if its discriminant is not
divisible by p and Sp+q=S g+i (mod p) ior q = l,. . ., n — 1, where Sk is the
sum of the kth powers of the n roots.

A. Hurwitz^^ gave an expression for the number A^ of real roots of

f{x)=aQ-\-aiX-\- . . . -\-arX''=0 (mod p),
where p is a prime. By Fermat's theorem,

-1

N=X \l-f{xy-'\ (modp).

a;=l

Letf{xy-'^ = Co-\-CiX+ .... Then N is determined by

Ar+l=Co+Cp_i+C2(,-i)+ . . . (mod p).

Letf(xi, X2) be the homogeneous form of f(x). Let A be the number of
sets of solutions of f{xi, a:2) = 0 (mod p), regarding {xi, X2) and (x/, X2) as
the same solution if Xi=pxi, X2=pX2 (mod p) for an integer p. Then

A-l= -0^-1-0^71+2^^:1^1 ao'^o. . Mr^r (mod p),

tto ! . . . a^ !

"Sitzungsber. Ak. Wiss. Wien (Math.), 110, Ila, 1901, 140-7.

"Kazani Izv. fiz. mat. Obsc. (Math. Soc. Kasan), (2), 12, 1902, No. 3, 33-49. Zap. mat. otd.

Obsc, 20, 1902, I-II.
"Archiv Math. Phys., (3), 5, 1903, 17-27.

232 History of the Theory of Numbers. [Chap, viii

where the summation extends over the sets of solutions ^ 0 of

ao+ai+- • .+a, = p — 1, ai + 2a2+. . .+ra^=0 (mod p-1).

The right member is an invariant modulo p oi f{xi, x^ with respect to all
linear homogeneous transformations on Xi, Xo with integral coefficients
whose determinant is not divisible by p. The final sum in the expression
for .4 — 1 is congruent to A^+1. If r = 2, p>2, the invariant is congruent
to the power (p — 1)/2 of the discriminant a^—^aQa^ of/.

*E. Stephan^^ investigated the number of roots of linear congruences
and systems of congruences.

H. Kuhne^ considered J{x)=x"'-\- . . .-\-a„ with no multiple irreducible
factor and with a^ not a multiple of the prime p. For n<m, let ^ = x'*+ . . .
+ 6„ have arbitrary coefficients. The resultant R{f, g) is zero modulo p
if and only if / and g have a common factor modulo p. Thus the number
of all ^'s of degree n which have no common factor with / modulo p is p„,
where

P,.^^\R{J, gYr (mod p':), co = p''-np-l),

the summation extending over the p" possible ^'s. He expressed p„ as
a sum of binomial coefficients. For any two binary forms 4>, \p of degrees
w, n, it is shown that

is invariant modulo p" under linear transformations with integral coeffi-
cients of determinant prime to p ; Ji is Hurwitz's^" invariant.

M. Cipolla^^ used the method of Hurwitz^^ to find the sum of the kth
powers of the roots of a congruence, and extended the method to show that
the number of common roots of /(x) = 0, g{x) = 0 (mod p), of degrees r, s, is
congruent to —XCjKi, where i, j take the values for which

0<i^s{p-l), 0<;^r(p-l), i+j=0 (mod p),

the Cs being as with Hurwitz, and similarly

g{xy-' = Ko+K^x+....

The number of roots common to n congruences is given by a sum.

L. E. Dickson^^ gave a two-fold generalization of Hurwitz's^^ formula for
the number of integral roots of f{x) = 0 (mod p) . The first generalization
is to the residue modulo p of the number of roots which are rational in a
root of an irreducible congruence of a given degree. A further generaliza-
tion is obtained by taking the coefficients Oi of f{x) to be elements in the
Galois field of order p'* (cf. Galois^^ etc.). Then let N be the number of
roots of f{x) = 0 which belong to the Galois field of order P = p"'". Then

"Jahresber. Staatsoberrealsch. Steyer, 34, 1903-4, 3-40.
"Archiv Math. Phys., (3), 6, 1904, 174-6.
«Periodico di Mat., 22, 1907, 36-41.
«BuU. Amer. Math. Soc, 14, 1907-8, 313.

Chap. VIII] NuMBER OF RoOTS OF CONGRUENCES. 233

N=N* (mod p), where A''*+l is derived from either of Hurwitz's two sums
for iV+1 by replacing p by P. The same replacement in Hurwitz's expres-
sion for A — 1 leads to the invariant A* — l, where A* is congruent modulo p
to the number of distinct sets of solutions in the Galois field of order p""*
of the equation /(xi, 0:2) =0.

G. Rados^'^ considered the sets of solutions of

fix, y) = i\a\i^^ x^'-^+ai'' x''-^+ . . . +05,^^2)2/^"'"'= 0 (mod p)

for a prime p. Let Ak denote the matrix of D, in (3), with a^ replaced
by ap\ Let C denote the determinant of order (p — iy obtained from D
by replacing ak by matrix A^. Then/=0 has a solution other than x^y=0
if and only if C is divisible by p ; it has exactly r sets of solutions other than
x=y=0 if and only if C is of rank (p — 1)^— r.

To obtain theorems including the possible solution x=i/=0, use

cf>{x, y) = S W^ x^-i+af V-2+ . . . +af.,)y''-^-'^Q (mod p),

a =

k=0

CL2 03

\ap_i+aoai

Op-3 Op-2 o,p-\ \

ap_2 Op.i+floO
ap_i+ao Oi 0

ap_3 ap_2 0 /

and tt/fc derived from a by replacing a^ by al^\ Let y be the determinant
derived from la| by replacing a^ by matrix a^; and 0 by a matrix whose p"^
elements are zeros. Then ^=0 has a set of real solutions if and only if
7=0 (mod p) ; it has r sets of solutions if and only if y is of rank p^—r.

*P. B. Schwacha^^ discussed the number of roots of congruences.

*G. Rados^^ treated higher congruences.

Theory of Higher Congruences, Galois Imaginaries.

C. F. Gauss/'' in a posthumous paper, remarked that "the solution of
congruences is only a part of a much higher investigation, viz., that of the
factorization of functions modulo p. Even when ^(x) = 0 has no real root,
^ may be a product of factors of degrees ^2, each of which could be said
to have imaginary roots. If use had been made of a similar freedom which
younger mathematicians have permitted themselves, and such imaginary
roots had been introduced, the following investigation could be greatly
condensed." As the later work of Serret^^ shows, such imaginaries can be

*'Arm. Sc. ficole Normale Sup., (3), 27, 1910, 217-231. Math. 6s Term^s firtesito (Report of

Hungarian Ac), Budapest, 27, 1909, 255-272.
"Ueber die Existenz und Anzahl der Wurzeln der Kongruenz Sc<x* = 0 (mod w), Progr. Wilher-

ing, 1911, 30 pp.
«Math. 6s. Term6s Ertesito, Budapest, 29, 1911, 810-826.
"Werke, 2, 1863, 212-240. Maser's German translation of Gauss' Disq. Arith., etc., 1889,

604-629.

234 History of the Theory of Numbers. [Chap, viii

introduced in a way free from any logical objections. Avoiding their use,
Gauss began his investigation by showing that two polynomials in xwith
integral coefficients have a greatest common divisor modulo p, which can
be found by Euclid's process. It is understood throughout that p is a
prime (cf. Maser, p. 627). Hence if A and B are relatively prime poly-
nomials modulo p, there exist two polynomials P and Q such that

PA+QB^l {mod p). "

Thus if A has no factor in common with B or C modulo p, we find by mul-
tiplying the preceding congruence by C that A has no factor in common
with the product BC modulo p. If a polynomial is divisible by A, B, C,. . .,
no two of which have a common factor modulo p, it is divisible by their
product.

A polynomial is called prime modulo p if it has no factor of lower degree
modulo p. Any polynomial is either prime or is expressible in a single
way as a product of prime polynomials modulo p. The number of distinct
polynomials x''+aa:"~^+ . . . modulo p is evidently p". Let (n) of these be
prime functions. Then p'^-l^d{d), where d ranges over all the divisors of
n (only a fragment of the proof is preserved). It is said to follow easily
from this relation that, if n is a product of powers of the distinct primes
a, 6, ... , then

n(n)=p"-2p"/''+2:p"/''^- ....

The rth powers of the roots of an equation P = 0 with integral coefficients
are the roots of an equation Pr = 0 of the same degree with integral coeffi-
cients. If r is a prime, P^=P (mod r).

A prime function P of degree m, other than x itself, divides x' — l for
some value of vKp"". If v is the least such integer, j^ is a divisor of p*" — 1.
Hence P divides

(1) x^"-^-l.

The latter is congruent modulo p to the product of the prime functions,
other than x, whose degrees are the various divisors of m.

If P = x"'—Ax"'~^-{'Bx"'~^— ... is a prime function modulo p, the re-
mainders by dividing the sum, the sum of the products by twos, etc., of

^ ^p ~p' ^p"*~^

by P are congruent to A, B, etc., respectively.

If V is not divisible by p and if m is the least positive integer for which
^"•=1 (mod v), each prime function dividing x" — ! modulo p is a divisor of
(1) and its degree is therefore a divisor of m. Let 6 be a divisor of m, and
5', 8", ... the divisors <d oi 8; let ai be the g. c. d. of v and p^-1, fx' the
g. c. d. of V and p*' — 1, . . . and set X' =iilii.' , \" =m/m", • • • • Then the num-
ber of prime divisors modulo p of degree 6 of a:" — 1 is iV/5, if A^ is the num-
ber of integers <y. which are divisible by no one of X', X", .... A method
of finding all prime functions dividing j"— 1 is based on periods of powers
of X with exponents < v and prime to v (pp. 620-2).

Chap. VIII] HiGHER CONGRUENCES, GaLOIS ImAGINARIES. 235

If X has been expressed as a product of relatively prime factors modulo
p, we can express X as a product of a like number of factors mod p" con-
gruent to the former factors modulo p. There is a fragment on the case
of multiple factors.

C. G. J. Jacobi" noted that, if g is a prime 6n — 1, x*+^=l (mod q) has
q — 1 imaginary roots a + 6V— 3, where a +36^=1 (modg), besides the roots
±1.

E. Galois®^ employed imaginary roots of any irreducible congruence
F(a;) = 0 (mod p), where p is a prime. Let i be one imaginary root of this
congruence of degree v. Let a be one of the p" — 1 expressions

a-\-aii+a2i^-\- . . . +a^-ii''~^

in which the a's are integers <p, not all zero. Since each power of a can
be expressed as such a polynomial, we have a" = 1 for some positive integer
n. Let n be a minimum. Then 1, a, . . . , a"~^ are distinct. Multiply them
by a new polynomial (3 ini; we get n products distinct from each other and
from the preceding powers of a. If 2n<p'' — 1, we use a new multiplier,
etc. Hence n divides p" — 1, and

(2) 0^"-^ = !.

[This is known as Galois's generalization of Fermat's theorem.] It follows
that there exist primitive roots a such that a^p^l if e<p'' — L Any primi-
tive root satisfies a congruence of degree v irreducible modulo p.

Every irreducible function F{x) of degree v divides x^''—x modulo p.
Since jF(x)[^"=F(xO modulo p, the roots of F{x)=0 are

All the roots of x^' = x are polynomials in a certain root ^, which satisfies
an irreducible congruence of degree v. To find all irreducible congruences
of degree v modulo p, delete from x^'' — x all factors which it has in common
with x^^—x, iJL<v. The resulting congruence is the product of the desired
ones; the factors may be obtained by the method of Gauss, since each of
their roots is expressible in terms of a single root. In practice, we find by
trial one irreducible congruence of degree v, and then a primitive root of
(2); this is done for p = 7, v = 3.

Any congruence of degree n has n real or imaginary roots. To find
them, we may assume that there is no multiple root. The integral roots
are found from the g. c. d. of F{x) and x^~^ — l. The imaginary roots of
the second degree are found from the g. c. d. oi F{x) and x^'~^ — l; etc.

V. A. Lebesgue^^ noted that, if p is a prime, the roots of all quadratic

"Jour, fiir Math., 2, 1827, 67; Werke, 6, 235.

"Sur la tMorie des nombres, Bulletin des Sciences Mathlmatiques de M. Ferussac, 13, 1830, 428.
Reprinted in Jour, de Math^matiques, 11, 1846, 381; Oeuvres Math. d'Evariste Galois,
Paris, 1897, 15-23; Abhand. Alg. Gleich. Abel u. Galois, Maser, 1889, 100.

"Jour, de Math^matiques, 4, 1839, 9-12.

236 History of the Theory of Numbers. [Chap, viii

congruences modulo p are of the form a-}-h\/n, where n is a fixed quadratic
non-residue of p, while a, b are integers. But the cube root of a non-cubic
residue is not reducible to this form a-\-hy/n. The p+1 sets of integral
solutions of y^ — nz'^=a (mod p) yield the p-|-l real or imaginary roots
x^y-[-zy/n of x^^=a (mod p). The latter congruence has primitive roots
if 0 = 1.

Th. Schonemann^ built a theory of congruences without the use of
Euclid's g. c. d. process. He began wath a proof by induction that if a
function is irreducible modulo p and divides a product AB modulo p, it
divides A or B. ■Much use is made of the concept norm NJ^ of f{x) with
respect to <i>{x), i. e., the product /(j8i) . . ./(i3^), where i3i,. . ., jS^ are the
roots of 4>{x)=0; the norm is thus essentially the resultant of / and 0.
The norm of an irreducible function with respect to a function of lower
degree is shown by induction to be not divisible by p. Hence if / is irre-
ducible and Nf^=0 (mod p), then/ is a divisor of 0 modulo p. A long dis-
cussion shows that if ai, . . . , a„ are the roots of an algebraic equation
/(x)=a:"-f . . . =0 and if /(a:) is irreducible modulo p, then niii]z— 0(a,)[
is a power of an irreducible function modulo p.

If a is a root of /(x) and f{x) is irreducible modulo p, and if 4>{a)
=^(a)-f-pi?(a), we write (p^^/ (mod p, a); then (f>{x)—\p{x) is divisible
by J{x) modulo p. If the product of two functions of a is =0 (mod p, a),
one of the functions is =0.

If /(x) =x'*-f ... is irreducible modulo p and if /(a) =0, then

/(a;) = (x-a)(x-a''). . .(x-a''""'), aP"-^=l (mod p, a),

n-l P"~'

x^ — 1 = n )x— 0,(a)|- (mod p, a),

where 4>i is a polynomial of degree n — 1 in a with coefficients chosen from
0, 1,. . ., p — 1, such that not all are zero. There exist (^(p" — 1) primitive
roots moduhs p, a, i. e., functions of a belonging to the exponent p" — 1.

Let F{x) be irreducible modulis p, a, i. e., have no divisor of degree ^ 1
modulis p, a. Let F{^) = 0, algebraically. Two functions of ^ with coeffi-
cients involving a are called congruent modulis p, a, j3 if their difference is
the product of p by a polynomial in a, /3. It is proved that

F{x)^ix-^){x-^n . ..{x-^^'"'-'"'), /3^'""^1 (mod p, a, ^).

If v<n, n being the degree of f(x), and if the function whose roots are
the (p"— l)th powers of the roots of /(x) is ^0 (mod p) for x = l, then /(a;)
is irreducible modulo p. Hence if ??? is a divisor of p — 1 and if g^ is a primitive
root of p, and if k is prime to m, then x"* — ^* is irreducible modulo p.

If p<m, m being the degree of F{x), and if the function whose roots are
the (p*^— l)th powers of the roots of F{x) is ^0 (mod p, a) for x = l, then

"Grundziige einer allgemeinen Theorie der hohem Congruenzen, deren Modul eine reelle
Primzahl ist, Progr., Brandenburg, 1844. Same in Jour, fiir Math., 31, 1846, 269-325.

Chap. VIII] HiGHER CONGRUENCES, GaLOIS ImAGINARIES. 237

F{x) is irreducible modulis p, a. Hence if m is a divisor of p"— 1, and if
^(a) is a primitive root of

a;^"-^=l (mod p, a),

and if k is prime to m, then x^ — g^ is irreducible modulis p, a.

If F(x, a) is irreducible modulis p, a, and if at least one coefficient satisfies

^p'-i^j (mod p, a)
if and only if j' is a multiple of n, then

1^(0^)= n F(a:, a^) (mod p, a)

y=o

has integral coefficients and is irreducible modulo p.

If G{x) is of degree mn and is irreducible modulo p, and G(a) = 0, alge-
braically, and if ^(a) is a primitive root of a;^'"''=l (mod p, a), then

X(a:)^n (x-F), < = r^ 6 = ^-^,

y=o p — 1

has integral coefficients and is irreducible modulo p.

The last two theorems enable us to prove the existence of irreducible
congruences modulo p of any degree. First,

(x'"-"-'-l)/{x'"'"'-'-l)

is the product of the irreducible functions of degree p" modulo p. To prove
the existence of an irreducible function of degree Zp", where I is any integer
prime to p, assume that there exists an irreducible function of each degree
<Zp", and hence for the degree a = ylp", where A=(f){l)<l. Let a be a
root of the latter, and r a primitive root of x^~^= 1 (mod p, a), where P = p'^.
Since I divides P — 1 by Euler's generalization of Fermat's theorem, x^ — r
is irreducible modulis p, a. Hence by the theorem preceding the last,
JI]Zq{x^ —r'^) is irreducible modulo p. Since its degree is Ip^'A, the last
theorem gives an irreducible congruence of degree Zp".

Every irreducible factor modulo p of x^"~^ — 1 is of degree a divisor of n.
Conversely, every irreducible function of degree a divisor of n is a factor
of that binomial. If n is a prime, the number of irreducible functions
modulo p of degree n" is (p"'— p""^" )/n\ If n is a product of powers of
distinct primes A, B,. . ., say four, the number of irreducible congruences
of degree n modulo p is

_ipABCD_pABC_ _pBCD\pABi A.pCD_pA_ _pD]

Tv

where p = p"/(^sc'Z)) Replacing p by p"*, we get the number of irreducible
congruences of degree n modulis p, a, where a is a root of an irreducible
congruence of degree m.

If n is a prime and p belongs to the exponent e modulo n,/= {x'' — \)/{x — \)
is congruent modulo p to the product of (n — l)/e irreducible functions of

238 History of the Theory of Numbers. [Chap, viii

degree e modulo p. Hence if p is a primitive root of n, / is irreducible
modulo p, and therefore with respect to each of the infinitude of primes
p+7«. Thus/ is algebraically irreducible.

Schonemann^^ considered congruences modulo p"*. If g{x) is not divis-
ible by p, and/=x''+ ... is irreducible modulo p"* and \i A{x) is not divisible
by/ modulo p, then/g'=A5 (mod p'") implies that B{x) is divisible by/
modulo p"*. If /=/i, ^=6^1 (mod p) and the leading coefficients of the four
functions are unity, while / and g have no common factor modulo p, then
/f/^/i^iCinod p'") impHes /=/i, g=g\ (mod p"*). He proved the final
theorem of Gauss. ^° Next, {x—aY-\-'pF{x) is irreducible modulo p^ if
and only if F{a)^0 (mod p) ; an example is

^ = {x-ir-'+pF{x), F(l) = l.

Henceforth, let/(a;) be irreducible modulo p and of degree n. If f{xY-\-'pF{x)
is reducible modulo p", then (p. 101) /(x) is a factor of F(a;) modulo p. If
/(a) = 0 and g(a) ^0 (mod p, a), then g'^ 1 (mod p'", a), where e = p'"~Hp''- 1).
If the roots of G{z) are the (p'"~^)th powers of the roots of /(x), then

G{z)^{z-^){z-n...{z-^'''-') (mod p-, a).

If M is any integer and if F{x) has the leading coefficient unity, we can
find z and w such that {x^—iy is divisible by F(x) modulo M.

A. Cauchy^® noted the uniqueness of the factorization of a function f{x)
with integral coefficients into irreducible factors modulo p, a prime. An irre-
ducible function divides a product only when it divides one factor modulo p.
A common divisor of two functions divides their g. c. d. modulo p.

Cauchy^^ employed an indeterminate quantity or symbol i and defined
f{i) to be not the value of the polynomial f{x) for x = i, but to be a-\-hi if
a-\-hx is the remainder obtained by dividing /(a:) by x^+1. In particular,
if /(x) is x^+1 itself, we have i^+1 =0.

Similarly, if w(x) = 0 is an irreducible congruence modulo p, a prime,
let i denote a sjmiboHc root. Then 0(i);/'(t) = O implies either </)(i) = 0 or
yp{i) = 0 (mod p). At most n integral functions of i satisfy /(x, i) = 0 (mod p),
if the degree of / in a: is nKp. If our co(x) divides x" — 1, but not x"* — 1,
m<n, modulo p, where n is not a divisor of p — 1, call i a symbolic primi-
tive root of x''=l (mod p). Then rc"-l=(.T-l)(x-i) . . . (x-i"-^) If
s is a primitive root of n and if n — l=gh, and p''= 1 (mod n),

equals a function of x with integral coefficients, while every factor of x" — 1
modulo p with integral coefficients equals such a product.

«Jour. fur Math., 32, 1846, 93-105.

"Comptes Rendus Paris, 24, 1847, 1117; Oeuvres, (1). 10, 308-12.

"Comptes Rendus Paris, 24, 1847, 1120; Oeuvres, (1), 10, 312-23.

Chap. VIII] HiGHER CONGRUENCES, GaLOIS ImAGINARIES. 239

G. Eisenstein^^ stated that if /(a;) = 0 is irreducible modulo p, and a is a
root of the equation /(x) = 0 of degree n, and if ao, ai,. . . are any integers,

K = ao-\-aia-\-. . . . +a„_ia"~-^
is congruent modulis p, a to one and but one expression

5 = 60/3+61^^+62/3^'+ . . . +6„_i/3^"-\

where the 6's are integers and /5 is a suitably chosen function of a. Hence
the p" numbers B form a complete set of residues modulis p, a. If co is a
primitive nth root of unity, and if

(/)(X) =a+ajV+co2V'+ . . . +cu^"-i^V""\

the product 0(X)0(X') ... is independent of a if X+X'+ ... is divisible by n.
Th. Schonemann^^ proved the last statement in case n is not divisible
by p. To make K = B, raise it to the powers p, p^,. . ., p"~^ and reduce
by j8^"=/3 (mod p, a). This system of n congruences determines /3 uniquely
if the cyclic determinant of order n with the elements hi is not divisible by
p; in the contrary case there may not exist a (3. The statement that the
expressions B form p" distinct residues is false if jS is a root of a congruence
of degree <n irreducible modulo p; it is true if /3 is a root of such a con-
gruence of degree n and if

i8+/3^+ . . . +/3^""'^0 (mod p, a).

J. A. Serref^" made use of the g. c. d. process to prove that if an irre-
ducible function F{x) divides a product modulo p, a prime, it divides one
factor modulo p. Then, following Galois, he introduced an imaginary
quantity i verifying the congruence F{i) = 0 (mod p) of degree v>l, but
gave no formal justification of their use, such as he gave in his later writings.
However, he recognized the interpretation that may be given to results
obtained from their use. For example, after proving that any polynomial
a{i) with integral coefficients is a root of a^''=a (mod p), he noted that this
result, for the case a = i, may be translated into the following theorem, free
from the consideration of imaginaries: If F{x) is of degree v, has integral
coefficients, and is irreducible modulo p, there exist polynomials f{x) and
x(x) with integral coefficients such that

x''''-x=f{x)F(x) +px{x).

The existence of an irreducible congruence of any given degree and any
prime modulus is called the chief theorem of the subject. After remarking
that Galois had given no satisfactory proof, Serret gave a simple and ingeni-
ous argument; but as he made use of imaginary roots of congruences without
giving an adequate basis to their theory, the proof is not conclusive.

'sjour. fur Math., 39, 1850, 182.

«'Jour. fiir Math., 40, 1850, 185-7.

"Cours d'algdbre sup6rieure, ed. 2, Paris, 1854, 343-370.

240 History of the Theory of Numbers. [Chap, viii

R. Dedekind"^ developed the subject of higher congruences by the
methods of elementary number theory without the use of algebraic prin-
ciples. As by Gauss^° he developed the theory' of the g. c. d. of functions
modulo p, a prime, and their unique factorization into prime (or irreducible)
functions, apart from integral factors. Two functions A and B are called
congruent modulis p, M, \i A—B is divisible by the function AI modulo p.
We may add or multiply such congruences. If the g. c. d. of A and B is
of degree d, Aij=B (mod p, M) has p'^ incongruent roots y{x) modulis p, M.

Let <t){M) denote the number of functions which are prime to M modulo
p and are incongruent modulis p, M. Let ii be the degree of M. A pri-
mary function of degree a is one in which the coefficient of a:" is = 1 (mod p).
If D ranges over the incongruent primary divisors of M, then 20(Z))=p''.
If M and A^ are relatively prime modulo p, then 4){MN) =4){M)<t){N). If
A is a prime function of degree a, 0(A'') =p*'(l -~ Vp")- If Af is a product
of powers of incongruent primary prime functions a,. . ., p,

*W=p-(i-l)...(i-l).

If F is prime to M modulo p, F'^^-^^^= 1 (mod p, M), which is the generaliza-
tion of Fermat's theorem. Hence if A is prime to M, the above Unear con-
gruence has the solution y=BA'^~^.

If P is a prime function of degree tt, a congruence of degree n modulis p,
P has at most n incongruent roots. Also

(3) y''-'-l^Il{y-F)^(mod p, P),

identically in y, where F ranges over a complete set of functions incongruent
moduhs p, P and not divisible by P. In particular, l+nF=0 (mod p, P),
the generalization of Wilson's theorem.

There are (/)(p'— 1) primitive roots modulis p, P. Hence we may em-
ploy indices in the usual manner, and obtain the condition for solutions
of ?/"=A (mod p, P), where A is not divisible by P. In particular, A
is a quadratic residue or non-residue of P according as

^(p'-i)/2^_^^ or -1 (mod p, P).

His extension of the quadratic reciprocity law will be cited under that topic.
A function A belongs to the exponent p with respect to the prime func-
tion P of degree tt if p is the least positive integer for which A^''=A (mod
p, P). Evidently p is a divisor of tt. Let N{p) be the number of incon-
gruent functions which belong to an exponent p which divides w. Then
p^='ZN'{d), where d ranges over the divisors of p. By the principle of
inversion (Ch. XIX),

isr(p) =p''-2p''/''+2:p''/''*-2p''/'''^+ . . .,

where a, 6, . . . are the distinct primes di\'iding p. Since the quotient of
this sum by its last term is not divisible by p, we have A^(p)>0.

"Jour, fiir Math., 54, 1857, 1-26.

■^

Chap. VIII] HiGHER CONGRUENCES, GaLOIS ImAGINARIES. 241

The product of the incongruent primary prime functions modulo p
whose degree divides tt is congruent modulo p to

Then, if xpip) is the number of primary prime functions of any degree p,
l!id\l/{d)=p', where the summation extends over all divisors d of tt. A com-
parison of this with XN{d)=p'' above shows that N{p)=p\l/{p). Another
proof is based on the fact that

(y-A){y-A')...{y-A''-')

is congruent modulis p, P to a polynomial in y with integral coefficients
which is a prime function. Moreover, if in (3) we associate the linear
factors in which the F's belong to the same exponent, we obtain a factor
of the left member which is irreducible modulo p.

The product of the incongruent primary prime functions of degree m
(m being divisible by no primes other than a, 6, . . . ) is congruent modulo p
to

\m\-'n.\m/ab\ . . .

Il\m/a\'Il\m/abc\

H. J. S. Smith^^ gave an exposition of the theory.
E. Mathieu,^^ in his famous paper on multiply transitive groups, gave
without proof the factorization (p. 301; for m = l, p. 275)

h{z^"'''-z)=u\(hzy"'^''-''+ihzy'"^''-''+ . ..+(hzy"'+hz+a},

a

where a ranges over the roots of a^'^^a, while /i^"*"=/i; and (p. 302; for
m = l,p. 280)

/^(gp'"" - z) =n(;i^ V" -hz-^),

where jS ranges over the roots of

If 12 is a root of a congruence of degree n whose coefficients are roots of
z'^"'=z and whose first member is prime to z^'^ — z, then (p. 303) all the roots
of z^""'=z are given by ^o+^i^+- • .+^„-il2''~\ where the A's satisfy

Z^ =Z.

J. A. Serret,'^^ in contrast to his^° earher exposition, here avoided at
the outset the use of Galois imaginaries. An irreducible function of degree
V modulo p divides x^—x modulo p if and only if v divides ^t. A simple

"British Assoc. Reports, 1860, 120, §§69-71; Coll. M. Papers, 1, 149-155.
"Jour, de Math6matiques, (2), 6, 1861, 241-323.

"M6m. Ac. Sc. de I'Institut de France, 35, 1866, 617-688. Same in Cours d'algfebre sup6-
rieure, ed. 4, vol. 2, 1879, 122-189; ed. 5, 1885.

242 History of the Theory of Numbers. [Chap, viii

proof is given for Dedekind's^^ final theorem on the product of all irreducible
functions of degree m modulo p.

A function F{x) of degree v, irreducible modulo p, is said to belong to the
exponent n if n is the least positive integer such that x" — 1 is divisible by
F{x) modulo p. Then n is a divisor of p" — 1, and a proper divisor of it,
since it does not divide p" — 1 for }x<v. Let n be a product of powers of the
distinct primes a, b,. . .. Then the product of all functions of degree v,
irreducible modulo p, which belong to an exponent n which is a proper
divisor of p" — 1, is congruent modulo p to

n(a:"/"-l)-n(x"/"'"^-l)...

and their number is therefore (f>{n)/v.

By a skillful analysis, Serret obtained theorems of practical importance
for the determination of irreducible congruences of given degrees. If we
know the N irreducible functions of degree /jl modulo p, which belong to
the exponent 1= (p" — l)/<i, then if we replace x by x^, where X is prime to d
and has no prime factor different from those which divide p" — 1, we obtain
the N irreducible functions of degree Xfi which belong to the exponent \l,
exception being made of the case when p is of the form 4ih — I, fi is odd, and
X is divisible by 4. In this exceptional case, we may set p = 2H — l, i'^2,
t odd; X = 2^s, j^2, s odd. Let k be the least of i, j. Then if we know
the A^/2^~^ irreducible functions of odd degree ju modulo p which belong to
the exponent I and if we replace x by x^, where X is of the form indicated,
is prime to d and contains only primes dividing p" — 1, we obtain N/2^~^
functions of degree Xju each decomposable into 2^~'^ irreducible factors,
thus giving A'' irreducible functions of degree \fx/2''~^ which belong to the
exponent XL Apply these theorems to x — g% which belongs to the exponent
(p — l)/d if ^ is a primitive root of p and if d is the g. c. d. of e and p — 1 ; we
see that x^—g^ is irreducible unless the exceptional case arises, and is then
a product of 2^"~^ irreducible functions. In that case, irreducible trinomials
of degree X are found by decomposing x" —g% where i' = 2'~^X.

If a is not divisible by p, a:'' — x — a is irreducible modulo p.

There is a development of Dedekind's theory of functions modulis p and
F(x), where F{x) is irreducible modulo p. Finally, that theory is considered
from the point of view of Galois. Just as in the theory of congruences of
integers modulo p we treat all multiples of p as if they were zero, so in
congruences in the unknown X,

(?(X, a:) = 0 (mod p, F(a:)),

we operate as if all multiples of F{x) vanish. There is here an indeter-
minate X which we can make use of to cause the multiples of F{x) to vanish
if we agree that this indeterminate x is an imaginary root i of the irreducible
congruence F(a:) = 0 (mod p). From the theorems of the theory of func-
tions modulis p, F{x), we may read off briefer theorems involving i (cf.
Galois^2)^

Chap. VIII] HiGHER CONGRUENCES, GaLOIS ImAGINARIES. 243

Harald Schiitz^^ considered a congruence

Z'^+aiX"-i+ . . . +a„=0 (mod Mix))

in which the a's and the coefficients of M are any complex integers
(cf. Cauchy,®^ for real coefficients). Let ai,..., a„ be the roots of the
corresponding algebraic equation. Let M = 0 have the distinct roots
III,. . ., jirn- Then the congruence has n"* distinct roots. For, let X — a^
=fi{x) have the factor x—jii, for i = 1, . . ., m. Taking i>l, we have

fi{^)=fl{^)+0.p-(lpi'

Set X = 111. Then the right member must vanish. Using these and /i (/^i) = 0 ,
we have m independent linear relations for the coefficients of /i(x).

C. Jordan^® followed Galois in employing from the outset a symbol for
an imaginary root of an irreducible congruence, proved the theorems of
Galois, and that, if j, ji, . . . are roots of irreducible congruences of degrees
p", q^,. . . where p, q, . . . are distinct primes, their product jji ... is a root
of an irreducible congruence of degree p^q^ ....

A. E. Pellet^^ stated that, if t is a root of an irreducible congruence of
degree v modulo p, a prime, the number of irreducible congruences of degree
Vi whose coefficients are polynomials in i is

— jp""! — Sp'"'i/5i+Sp'"'i/9i«2— ...+( — l)"'p''V9i- ■ -Sm }

if qi,..., qm are the distinct primes dividing vi. Of these congruences,
4){n)/vi belong to the exponent n if n is a proper divisor of (p")"' — L

Any irreducible function of degree ix modulo p with integral coefficients
is a product of 5 irreducible factors of degree ix/b with coefficients rational
in i, where b is the g. c. d. of fx, v.

In an irreducible function of degree vi and belonging to the exponent n
and having as coefficients rational functions of i, replace x by x^, where X
contains only prime factors dividing n; the resulting function is a product of
2^~^D/n irreducible functions of degree \nvi/{2^~^D) belonging to the
exponent \n, where D is the g. c. d. of \n and p""* — 1, and 2^~^ is the highest
power of 2 dividing the numerators of each of the fractions (p'"''+l)/2 and
Xn/(2Z)) when reduced to their lowest terms.

Let gf be a rational function of i, and m the number of distinct values
among g, g^, g^ ,. . .. If neither g-{-g^-{- . . . +9'^"*" nor v/m is divisible by
p, then x^ — x — g is irreducible; in the contrary case it is a product of
linear functions.

Hence if we replace a; by x^ — x in an irreducible function of degree /x
having as coefficients rational functions of i, we get a new irreducible
function provided the coefficient of x''~^ in the given function is not zero.

^^Untersuchungen liber Functionale Congruenzen, Diss. Gottingen, Frankfurt, 1867.
^«Trait^ des substitutions, 1870, 14-18.
"Comptes Rendus Paris, 70, 1870, 328-330.

244 History of the Theory of Numbers. [Chap, viii

[Proof in Pellet.®^] In particular, if p is a primitive root of a prime n,
we have the irreducible function, modulo p,

(xP-a;)"-l
x^'-x-l

C. Jordan^^ listed irreducible functions [errata, Dickson,^"'^ p. 44].

J. A. Serret'^^ determined the product F„ of all functions of degree p"
irreducible modulo p, a prime. In the expansion of (^ — 1)" replace each
power ^^" by x" ; denote the resulting polynomial in x by X^. Then

X.,rn^\{^-irl=ie"'-^y, X.m^X^^'^-X (mod p).

Hence Vn = Xpr^/Xpn-i. Moreover,

X,+i = (^-l)''+^ = $a-ir-(^-l)''^Z/-X, (modp).

Multiply this by the relations obtained by replacing /ibyju+1,- • .,iJi+v — l.
Thus

X,+.^Z,(X/-i-l)(X,^;J -1) . ..{X:+l,-l) (mod p).

Take /i = p"~\ /x+i' = p". Hence

F„^' "ff" A (mod p), A = Xjnii+x-i-l.

X=l

Each /x decomposes into p — 1 factors X—g where ^ = 1,..., p — 1. The
irreducible functions of degree p" whose product is A are said to belong to
the Xth class. When x is replaced by x^—x, X^ is replaced by X^+i since ^'
is replaced by ^'(^ — 1) and hence (^ — 1)" by (^ — l)""*"^; thus A is replaced
by A+i) while the last factor in F„=nA is replaced by Xpn —1, which is
the first factor in Vn+i- Hence if F{x) is of degree p" and is irreducible
modulo p and belongs to the Xth class, F{x^—x) is irreducible or the product
of p irreducible functions of degree p" according as X= or <p'*— p"""\

For n = l, the irreducible functions of the Xth class have as roots poly-
nomials of degree X in a root of i^ — i=l, which is irreducible modulo p.
Hence if we eliminate i between the latter and f{i) = x, where f{i) is the
general polynomial of degree X in i, we obtain the general irreducible
function of degree p of the Xth class.

For any n, the determination of the irreducible functions of degree p" of
the first class is made to depend upon a problem of elimination (Algebre,
p. 205) and the relation to these of the functions of the Xth class, X>1, is
investigated.

G. Bellavitis'^" tabulated the indices of Galois imaginaries of order 2
for each prime modulus p = 4n+3^63.

Th. Pepin^" proved that x^ — ny^=l (mod p) has p + 1 sets of solutions

'Kllomptes Rendus Paris, 72, 1871, 283-290.

"Jour, de Mathdmatiques, (2), 18, 1873, 301^, 437-451. Same as in Cours d'alg^bre sup^rieure,

ed. 4, vol. 2, 1879, 190-211.
"f-Atti Accad. Lincei, Mem. Sc. Fis. Mat., (3), 1, 1876-7, 778-800.
««Atti Accad. Pont. Nuovi Lincei, 31, 1877-8, 43-52.

Chap. VIII] HiGHER CONGRUENCES, GaLOIS ImAGINARIES. 245

X, y selected from 0, 1, . . . , p — 1, provided n is a quadratic non-residue of the
prime p. Then x-\-y\/n is a root of p+^=l (mod p), which therefore has
p + 1 complex roots, all a power of one root. There is a table of indices for
these roots when p = 29 and p = 41. [Lebesgue.^^]

A. E. Pellet^^ considered the product A of the squares of the differences
of the roots of a congruence /(x) = 0 (mod p) having no equal roots. Then
A is a quadratic non-residue of p if f{x) has an odd number of irreducible
factors of even degree, a quadratic residue if f{x) has no irreducible factor
of even degree or has an even number of them. For, if 5i, . . ., 5^ are the
values of A for the various irreducible factors of f{x), then A=a^di. . .5j
(mod p), where a is an integer. Hence it suffices to consider an irreducible
congruence /(a:) = 0 (mod p). Let v be its degree and i a root. In

v-i i-i

!/=n n {x'' -x^)

1=1 A; = 0

replace x by the v roots; we get two distinct values if v is even, one if ;^ is
odd. In the respective cases, i/^=A (mod p) is irreducible or reducible.

R. Dedekind^^ noted that, if P(x) is a prime function of degree / modulo
p, a prime, a congruence F{x) = 0 (mod p, P) is equivalent to the congruence
F(a) = 0 (mod tt), where tt is a prime ideal factor of p of norm p^, and a is
a root of P(a) = 0 (mod tt).

A. E. Pellet^^ denoted by/(a;)=0 the equation of degree ^(A;) having
as its roots the primitive A;th roots of unity, and by /i(i/) =0 the equation
derived by setting y = x-\-\/x. If p is a prime not dividing k, f{x) is con-
gruent modulo p to a product of <f>{k)/v irreducible factors whose degree v
is the least integer for which p" — ! is divisible by k. li fi{y) = 0 (mod p)
has an integral root a,f(x) is divisible modulo p by x^ — 2ax-\-l. Either the
latter has two real roots and f{x) and fi{y) have all their roots real and
p — 1 is divisible by k, or it is irreducible and f(x) is a product of quadratic
factors modulo p and the roots oifi{y) are all real and p+1 is divisible by k.
If k divides neither p+l nor p — l,fi{y) is a product of factors of equal
degree modulo p. [Cf. Sylvester,^^ etc., Ch. XVI.]

Let A; be a divisor f^ 2 of p + L Let X be an odd number divisible by no
prime not a factor of k, and relatively prime to{p+l)/k. Then x^^ — 2ax^ + 1
is irreducible modulo p [Serret,^^ No. 355]. Also, if h is not divisible by p

F={x-\-by''-2aix^-b^)^+ix-by^

is irreducible modulo p; replacing x^ by y, we obtain a function of degree X
irreducible modulo p. If /c is a divisor ?^2 of p — 1 and if X is odd, prime to
{p — l)/k and divisible by no prime not a factor of k, F decomposes modulo
p into two irreducible functions of degree X.

The function /(x^) is either irreducible or the product of two irreducible
factors of degree v. In the respective cases, the product A of the squares of

"Comptes Rendus Paris, 86, 1878, 1071-2.

"Abhand. K. Gesell. Wiss. Gottingen, 23, 1878, p. 25. Dirichlet-Dedekind, Zahlentheorie, ed.

4, 1894, 571-2.
s^Comptes Rendus Paris, 90, 1880, 1339-41.

246 History of the Theory of Numbers. [Chap, viii

the differences of the roots of /(x") = 0 is a quadratic non-residue or residue
of p [Pellet^^j. Let Ai be the like product for J{x). Then A = (-l)'2-'
/(0)Ai". Hence /(ax- +6) is irreducible if ( — l)7(6)/a'' is a quadratic non-
residue and then /(ax '+6) is irreducible modulo p for every i and even v.

0. H. Mitchell^ gave analogues of Fermat's and Wilson's theorems
moduhs p (a prime) and a function of x.

A. E. Pellet^ considered the exponent n to which belongs the product P
of the roots of a congruence F(x) = 0 of degree v irreducible modulo p.
If g is a prime factor of n, F(x') is irreducible or the product of q irreducible
factors of degree v modulo p according as q is not or is a divisor of {p — \)/n.
In particular, F{x^) is irreducible modulo p if, for v even, X contains only-
prime factors of n not dividing {p — \)/n; for v odd, we can use the factor 2
in X only once if p = 4mH-l. Let i be a root of F(x) = 0, I'l a root of an
irreducible congruence Fi(x) = 0 (mod p) of degree v^ prime to v. Then
ill is a root of an irreducible congruence G(x) = 0 (mod p) of degree vvx.
F{x) belongs to the exponent Nn modulo p, where n is prime to (p'— 1)
-^\{p — \)N\. Let qi be a prime factor of .V not dividing p — 1. Then
G(x'') is irreducible or decomposes into qi irreducible factors of degree vvi
according as qi is not or is a divisor of (p'' — l)/N. Thus G(x^) is irreducible
if X contains onlj' prime factors of N dividing neither p — 1 nor {p'' — l)/N.

0. H. MitchelP^ defined the prime totient of /(x) to mean the number
of polynomials in x, incongruent modulo p, of degree less than the degree of
(x) and having no factor in conmion with / modulo p. Those which
contain S, but no prime factor of / not contained in S, are called >S-totitives
of/.

C. Dina^^ proved known results on congruences moduhs p and F{x).

A. E. Pellet^^ proved that, if ju distinct values are obtained from a
rational function of x with integral coefficients by replacing x successively
by the 77i roots of an irreducible congruence modulo p, then ^i is a divisor
of m and these /jl values are the roots of an irreducible congruence. Thus
if A is a rational function of any number of roots of congruences irreducible
modulo p, and p is the number of distinct values among A, A^, A^\. . .,
these values satisfy an irreducible congruence modulo p. If A belongs to
the exponent n modulo p, then v is the least positive integer for which p''= 1
(mod n). He proved a result of Serret's^^ stated in the following form: If,
in an irreducible function F{x) modulo p of degree v and exponent n, x is
replaced by x^, where X contains only primes dividing n, then F(x^) is a
product of irreducible factors of degree vq and exponent n\, where q is the
least integer for which ^"^=1 (mod n\). He proved the first theorem of
Pellet^ and the last one of Pellet."

"Johns Hopkins University Circulars, 1, 1880-1, 132.

"Comptps Rendus Paris, 93, 1881, 1065-6. Cf. Pellet."

"Amer. Jour. Math., 4, 1881, 25-38.

•^Giomale di Mat., 21, 1883, 234-263. For comments on 263-9, see the chapter on quadratic

reciprocity law.
««Bull. Soc. Math. France, 17, 1888-9, 156-167.

Chap. VIII] HiGHER CONGRUENCES, GaLOIS ImAGINARIES. 247

E. H. Moore^^ stated that every finite field (Korper) is, apart from nota-
tions, a Galois field composed of the p" polynomials in a root of an irreducible
congruence of degree n modulo p, a prime.

E. H. Moore^° proved the last theorem and others on finite fields.

K. Zsigmondy^^ noted that the number of congruences of degree n
modulo p, having no irreducible factor of degree i, is

P"-({)p"-^+(2)p"-''

where / is the number of functions of degree i irreducible modulo p.

G. Cordone^^ noted that if a function is prime to each of its derivatives
with respect to each prime modulus Pi,..., Pn and is irreducible modulo
M = piK . .pn", it is irreducible with respect to at least one of Pi,..., Pn-
If F(x) is not identically =0 modulo pi, nor modulo p2, etc., and if it
divides a product modulo M and is prime to one factor according to each
modulus Pi,. . ., Pn, then F(x) divides the other factor modulo M.

Let F{x) be a function of degree r irreducible with respect to each prime
Pi, . . ., Pn, while /(x) is not divisible by F{x) with respect to any one of the
p's, then (pp. 281-8)

l/(x)[-^^^^^l (mod M, F(x)), 0,(M)=M'-(l-^,y . .(l-^),

<}>r{M) being the number of functions Cix''~^+ . . . -\-Cr, in which the c's take
such values 0, 1,. . ., M — 1 whose g. c. d. is prime to M. Let A be the
product of these reduced functions modulis M, F{x). Then (pp. 316-8),
A= — 1 (mod M, F) if M = p^, 2p^ or 4, where p is an odd prime, while
A= + l in all other cases.

Borel and Drach^^ gave an exposition of the theory of Galois imaginaries
from the standpoint of Galois himself.

H. Weber^^ considered the finite field (Congruenz Korper) formed of the
p" classes of residues modulo p of the polynomials, with integral coefficients,
in a root of an irreducible equation of degree n. He proved the generaliza-
tion of Fermat's theorem, the existence of primitive roots, and the fact that
every element is a square or a sum of the squares of two elements.

Ivar Damm^* gave known facts about the roots of congruences modulis
p, /(x), where /(x) is irreducible modulo p, without exhibiting the second
modulus and without making it clear that it is not a question of ordinary
congruences modulo p. Let e be a fixed primitive root of the prime p.
Then the roots of every irreducible quadratic congruence are of the form
a± hoi, where co^ = e. Let k^^^ = e, ki = k^.

89Bull. New York Math. Soc, 3, 1893-4, 73-8.

•"Math. Papers Chicago Congress of 1893, 1896, 208-226; University of Chicago Decennial

Publications, (1), 9, 1904, 7-19.
"El Progreso Matemdtico, 4, 1894, 265-9.
"Introd. th^orie des nombres, 1895, 42-50, 58-62, 343-350.
•'Lehrbuch der Algebra, II, 1896, 242-50, 259-261; ed. 2, 1899, 302-10, 320-2.
"Bidrag till Laran om Kongruenser med Primtalsmodyl, Diss., Upsala, 1896, 86 pp.

248 History of the Theory of Numbers. [Chap, viii

Analogous to the definition of trigonometric functions in terms of expo-
nentials, he defined quasi cosines and sines by

and Tqx as their quotient. Their relations are discussed. He defined
pseudo cosines and sines by

Cpx = Cq[{p - l)x] = e-'Cq2x, Spx = -e-'Sq2x.

For each prime p<100, he gave (pp. 65-86) the (integral) values of

e^, ind x, Cqx, Sqx, Tqx, Cpx, Spx

for x=l, 2,. . ., p + 1.

L. E. Dickson^^ extended the results of Serret^* to the more general case
in which the coefficients of the functions are poljTiomials in a given Galois
imaginary (i. e., are in a Galois field of order p"). For the corresponding
generaUzation of the results of Serret^^ on irreducible congruences modulo
p of degree a power of p, additional developments were necessary. To
obtain the irreducible functions of degree p in the GFlp'^'] which are of the
first class, we need the complete factorization, in the field,

hiz^'-z-v) =U{h''z''-hz-^)
where hv is an integer and /S ranges over the roots of

all of whose roots are in the field. For the case v = 0 this factorization is
due to ]Mathieu." Thus K^z^—hz—^ is irreducible in the field if and only
if B^O. In particular, if /3 is an integer not divisible by p, z^ — z—^ is
irreducible in the GF[p"] if and only if n is not divisible by p.

R. Le Vavasseur^^ employed Galois imaginaries to express in brief no-
tation the groups of isomorphisms of certain tj-pes of groups, for example,
that of the abelian group G generated by n independent operators ai, . . .,
a„, each of period a prime p. If i is a root of an irreducible congruence
of degree n modulo p, and if j = ai-\-ia2+ . . .+i''~^a„, he defined a^ to be
Oi"' . . . an"". Then the operators of G are represented by the real and
imaginary powers of a.

A. Guldberg^^ considered linear differential forms

A d^y , , dy ,
^y=^>:d^.-^----^^^di+^oy,

^4th integral coefficients. The product of two such forms is defined by
Boole's sjTnbolic method to be

d'' 6} d

Ay'By={au-^-\- • • • +«o)(^/^+ • • • +^^+^o)2/.

"BuU. Amer. Math. Soc.,3, 1896-7, 381-9.
"M^m. Ac. Sc. Toulouse, (9), 9, 1897, 247-256.
"^Comptes Rendus Paris, 125, 1897, 489.

Chap. VIII] HiGHER CONGRUENCES, GaLOIS ImAGINARIES. 249

If the product is =Cy (mod p), Ay and By are called divisors modulo p
of Cy. Let A?/ be of order n and irreducible modulo p. Then Ay is con-
gruent modulis p, A?/ to one and but one of the p" forms

(4) s'c,^ (c, = 0, l,...,p-l).

If It is any one of these forms (4) and if e = 'p^ — \, Guldberg stated the
analogue of Fermat's theorem

dfu

^='M (mod p, ^y),

but incorrectly gave the right member to be unity [cf. Epsteen/''^, Dickson^"^].
L. Stickelberger^^ considered F{x) =x^+aix''~^-\- . . . with integral coeffi-
cients, such that the product D of the squares of the differences of the roots
is not zero. Let p be any prime not dividing D. Let v be the number of
factors of F{x) which are irreducible modulo p. He proved by the use of
prime ideals that

(f)=(-i)»-.

where the symbol in the left member is that of Legendre [see quadratic
residues].

L. E. Dickson^^ proved the existence of the Galois field GF[p''] of order
p" by induction from r = n to r = qn, by showing that

(a:^"'-a:)/(x^"-x)

is a product of factors of degree q belonging to and irreducible in the
(?F[p"]. Any such factor defines the GF[p'"'].

L. Kronecker^°° treated congruences modulis p, P{x) from the stand-
point of modular systems.

F. S. Carey ^°^ gave for each prime p< 100 a table of the residues of the
first p + 1 powers of a primitive root a-\-hj of z^~^=l (mod p) where /=»'
(mod p), V being an integral quadratic non-residue of p. The higher powers
are readily derived. While only the single modulus p is exhibited, it is
really a question of a double modulus p and x^—v. Methods of "solving"
2?"-!=! are discussed. In particular, for n = 3, there is given a primitive
root for each prime p< 100.

L. E. Dickson^"^ gave a systematic introductory exposition of the theory,
with generalizations and extensions.

M. Bauer^"^ proved that, if /(a;) =0 is an irreducible equation with inte-
gral coefficients and leading coefficient unity, w a root, D its discriminant,
d = D/k^ that of the domain defined by w, p sl prime not dividing k, x>l,

«8Verhand. I. Internat. Math. Kongress, 1897, 186.

"^BuU. Amer. Math. Soc, 6, 1900, 203-4.

looVorlesungen iiber Zahlentheorie, I, 1901, 212-225 (expanded by Hensel, p. 506).
i"Proc. London Math. Soc, 33, 1900-1, 294-310.

lo'Linear groups with an exposition of the Galois field theory, Leipzig, 1901, pp. 1-71.
lo^Math. Naturw. Berichte aus Ungarn, 20, 1902, 39-42; Math. 6s Phyp. Lapok, 10, 1902, 28-33.

250 History of the Theory of Numbers. [Chap, viii

then f{x) is congruent modulo p" to a product of Fi(j),. . ., F,(a:), each
irreducible modulo p°, such that F,(x)=/,(a:)'« (mod p), where /(x)= 11/. (x)*'
(mod p), and /.(x) is irreducible modulo p. There is an example of an
irreducible cyclotomic function reducible with respect to every prime power
modulus.

P. Bachmann^^ gave an exposition of the general theory.

G. Arnoux^"^ exhibited in the form of tables the work of finding a primi-
tive root of the GF\1^] and of the GF[5^], and tabulated the reducible and
irreducible congruences of degrees 1, 2, 3, modulo 5.

S. Epsteen^°^ proved the result of Guldberg,^" and developed the theory
of residues of hnear differential forms parallel to the theory of finite fields,
as presented by Dickson. ^°-

L. E. Dickson ^°^ noted that the last mentioned subjects are identical
abstractly. Let the irreducible form A?/ be

d'^y dy

To the element (4) we make correspond the element 2c,z* of the Galois
field of order p", where z is a root of the irreducible congruence

5„2"+...+5i2+5o=0 (mod p).

Since product relations are preserved by this correspondence, the p" resi-
dues (4) define a field abstractly identical with our Galois field.

Dickson^"^'' proved that x'"=.t (mod vi = p") has p and only p roots if p is
a prime and hence does not define the Galois field of order m as occasionally
stated.

A. Guldberg^"^'' employed the notation of finite differences and wrote

n m n m

Fy, = 2 afi%, Gy, = 2 hj9%, Fy^.Gy, = 2 afi\ 2 bfi%,

t=0 »=0 t=0 »=0

where 6y^ = yjc+i, ^'?/x = 2/1+2. • • •> symbolically. To these linear forms with
integral coefficients taken modulo p, a prime, we may apply EucUd's g. c. d.
process and prove that factorization is unique. Next, let 6„, be not di\'isible
by p, so that Gy^ is of order m. With respect to the two moduU p, Gy^, a
complete set of p"* residues of hnear forms is a„,_i?/:r+m-i+ ■ • • +ao2/x (^1 = 0,
1,..., p-1). Amongst these occur <}>{Gy^) =p"'{l- 1 /p'"') .. .{1-1 /p"''^)
forms Fy^. prime to Gyj^ if Wi, . . . , niq are the orders of the irreducible factors
of Gyx modulo p, and

FyJ'^^'^^-^^y, (mod p, Gy,)

In particular, if Gy^ is irreducible and of order m,

Fyr-'^yAmodp,Gy,).

i

i«Niedere Zahlentheorie, 1, 1902, 363-399.

»»Assoc. frang. av. sc, 31, 1902, II, 202-227.

i«BuU. Amer. Math. Soc, 10, 1903-4, 23-30.

'"/bid., pp. 30-1.

"'"Amer. Math. Monthly, 11, 1904, 39-40. ^

>»"f'.\iinaU di Mat., (3), 10, 1904, 201-9. ■

Chap. VIII] HIGHER CONGRUENCES, GaLOIS ImAGINARIES. 251

W. H. Bussey^°^ gave for each Galois field of order < 1000 companion
tables showing the residues of the successive powers of a primitive root,
and the powers corresponding to the residues arranged in a natural order.
These tables serve the same purposes in computations with Galois fields
that tables of indices serve in computations with integers modulo p", where
p is a prime.

G. Voronoi^°^ proved the theorem of Stickelberger.^^ Thus, for n = 3,
(D/p) = — 1 only when v = 2. Hence a cubic congruence has a single root
if (D/p) = —1, and three real roots or none if {D/p) = +1.

P. Bachmann^^° developed the general theory from the standpoint of
Kronecker's modular systems and considered its relation to ideals (p. 241).

M. Bauer^^^ employed a polynomial /(z) of degree n irreducible modulo
p, and another one M{z) of degree less than that of f{z) and not divisible
by/(2) modulo p. Then if {t, a) = l, the equation

/(2)+p«M(2)=0

is irreducible. The case a = 1 is due to Schonemann^^ (p. 101).

G. Arnoux,^^^ starting with any prime m and integer n, introduced a
symbol i such that i^^^ 1 (mod m) and such that i, i^, . . ., i^ are distinct,
where s = m" — 1, without attempting a logical foundation. If /(x) is irre-
ducible modulo m and of degree n, there is only a finite number of distinct
residues of powers of x modulis/(x), m] let x^ andx'^'^^have the same residue.
Thus x^ — 1 is divisible by/(x) modulo m. It is stated (p. 95) without proof
that p divides s. "Call a a root of /(a:) = 0. To make a coincide with the
primitive root i of a;^= 1, we must take p = s, whence every such primitive
root is a root of an irreducible congruence of degree n modulo m." Follow-
ing this inadequate basis is an exposition (pp. 117-136) of known properties
of Galois imaginaries.

L. I. Neikirk^^^ represented geometrically the elements of the Galois
field of order p" defined by an irreducible congruence

/(x) =rc"+aia:"-^H- . . . -fa„=0 (mod p).

Let j be a root of the equation f{x) = 0 and represent

Ci/~^+ . . . +c„_ii-Fc„ (c's integers)

by a point in the complex plane. The p"" points for which the c's are chosen
from 0, 1, . . ., p — 1 represent the elements of the Galois field.

G. A. Miller^^^ listed all possible modular systems p, 4>{x), where p is a
prime and the coefficient of the highest power of x is unity, in regard to
which a complete set of prime residues forms a group of order ^12. If
4>{x) is the product of k distinct irreducible functions 4>i, . . . , (f)^ modulo p,

"SBuU. Amer. Math. Soc, 12, 1905, 21-38; 16, 1909-10, 188-206.

lO'Verhand. III. Internat. Math. Kongress, 1905, 186-9.

""AUgemeine Arith. d. Zahlenkorper, 1905, 81-111.

"iJour. fur Math., 128, 1905, 87-9.

"'Arithm^tique Graphique, Fonctiona Arith., 1906, 91-5.

"'BuU. Amer. Math. Soc, 14, 1907-8, 323-5.

"«Archiv Math. Phys., (3), 15, 1909-10, 115-121.

252 History of the Theory of Numbers. [Chap, viii

the residues prime to p, (t>{x) constitute the direct product of the groups
with respect to the various p, 0.(a:). Not every abelian group can be repre-
sented as a congruence group composed of a complete set of prime residues
with respect to Fj, . . ., Fx, where the F's are functions of a single variable.

Mildred Sanderson^ ^^ employed two moduU m and P{y), the first being
any integer and the second any polynomial in y with integral coefficients.
Such a polynomial /(?/) is said to have an inverse /i (y) if //i= 1 (mod m, P).
If P{y) is of degree r and is irreducible with respect to each prime factor of
m, a function f{y), whose degree is <r, has an inverse moduhs m, P{y), if
and only if the g. c. d. of the coefficients of /(?/) is prune to m. For such
an/, /" = 1 (mod vi, P), where n is Jordan's function Jr{fn) [Jordan, ^"^
Ch. V]. In case m is a prime, this result becomes Galois'^^ generalization
of Fermat's theorem. The product of the n distinct residues having
inverses moduHs m, P{y), is congruent to —1 when m is a power of an odd
prime or the double of such a power or when r= 1, w = 4; but congruent to
+ 1 in all other cases — a two-fold generahzation of Wilson's theorem.
There exists a polynomial P{y) of degree r which is irreducible with respect
to each prime factor of m. Then if A{y), B{y) are of degrees <r and their
coefficients are not all divisible by a factor of m, there exist polynomials
a(i/), ^{y), such that aA+/3B=l (mod m, P).

Several writers^^^ discussed the irreducible quadratic factors modulo p
of {x'^—\)/{x^ — l), where A' = 1 or 2, p is a prime, a a divisor of p-fl.

G. Tarry^^^ noted that, if f=q (mod m), where 5 is a quadratic non-
residue of the prune m, the Galois imaginary a+hj is a primitive root if
its norm {a-\-'bj){a — hj) is a primitive root of m and if the ratio a:h and the
analogous ratios of the coordinates of the first m powers of a-\-hj are incon-
gruent.

L. E. Dickson^ ^^ proved that two polynomials in two variables with
integral coefficients have a unique g. c. d. modulo p, a prime. Thus the
unique factorization theorem holds.

G. Tarr>'^^^ stated that Ap is a primitive root of the GF[p^] if the norm
of A = a-\-'bj is a primitive root of p and if the imaginar>^ p belongs to the
exponent p+1. The 0(p-f 1) numbers p are found by the usual process
to obtain the primitive roots of a prime.

U. Scarpis^-° proved that an equation of degree v irreducible in the
Galois field of order p" has in the field of order p"*" either v roots or no
root according as v is or is not a di\dsor of m [Dickson^°^, p. 19, lines 7-9].

Cubic Congruences.
A. Cauchy^^° solved y'^-\-By-\-C={) (mod p) when it has three distinct

'"Annals of Math., (2), 13, 1911, 36-9.

"•L'interm^diaire dea math., 18, 1911, 195, 246; 19, 1912, 61-69, 95-6; 21, 1914, 158-161; 22,

1915, 77-8. Sphinx-Oedipe, 7. 1912, 2-3.
"'Assoc, fran^. av. sc, 40, 1911, 12-24. "sBuU. Amer. Math. Soc, (2), 17, 1911, 293-4.

"'Sphinx-Oedipe, 7, 1912, 43^, 49-50. ""AnnaU di Mat., (3), 23, 1914, 45.

""Exercices de Math., 4, 1829, 279-292; Oeuvres, (2), 9, 326-333.

Chap. VIII] CuBIC CONGRUENCES. 253

integral roots y^, 2/2, Vs, and p is a prime = 1 (mod 3), and B^O (mod p) . Set

^Vi = yi+ry2-\-r%, ^V2 = yi+r^y2+ry3, r^+r+ 1=0 (mod p).

The roots of u^-\-Cu—B^/27= 0 (mod p) are Ui = ^i^, U2 = ^2^. After finding
Vi from Vi^=Ui (mod p), we get V2= —B/{3vi), and determine the y's from
'2yi=0 and the expressions for 3^1, Sv2. Thus

2/i=yi+z;2, y2=r\+rv2, ys^rvi+r^ (mod p).

Since by hypothesis the cubic congruence has three distinct integral roots,
the quadratic has two distinct integral roots, whence

p-l P-l 7^2 ^3

"^"^7 ' +(~^+^7 ' ^2' ^ ' ^^ (modp).

Conversely, if the last two conditions are satisfied, the cubic congruence
has three distinct real roots provided p=l (mod 3), B^O (mod p).

G. Oltramare^^^ found the conditions that one or all of the roots of
x^+Spx+2q=0 (mod fx) given by Cardan's formula become integral modulo
fx, a prime. Set

D = q^-\-p\ a=-q+VD, T=-q-VD,

First, let /x be a prime 6n — 1 . If D is a quadratic residue of /x, there
is a single rational root — 2g/(p+(r^"+T^"). If Z) is a quadratic non-residue
of fx, there are three rational roots or no root according as the rational part
M of the development of o-^"~^ by the binomial theorem satisfies or does not
satisfy ilfp^+g^O (mod //) ; if also /x = 18m+ll and there are three rational
roots, they are

2M^, -^(M±iW-3i)),

if (72"*+i = ikf 4-iVVD; with a like result when m = 18m+5.

Next, let /x = 6n+l. If Z) is a quadratic non-residue of ^x, there is one
rational root or none according as the rational part M of the development
of o-^" is or is not such that

(2M-l)2(ikf+l)=-2gVp3 (modM),

and if a rational root exists it is 2q/ \ p {2M — 1 ) } . If Z) is a quadratic residue
of IX, there are three rational roots or none according as cr^''= 1 (mod /x)
or not. When there are three, they are given explicitly if ^t=18m-|-7 or
18m + 13, while if // = 18m + l there are sub-cases treated only partially.

G. T. Woronoj^^^ (or Voronoi) employed Galois imaginaries a -{-hi, where
i^—N=0 (mod p) is irreducible, p being an odd prime, to treat the solution of

x^—rx — s=0 (mod p).

I'lJour. fiir Math., 45, 1853, 314-339.

'"Integral algebraic numbers depending on a root of a cubic equation (in Russian), St. Peters-
burg, 1894, Ch. I. Cf. Fortschritte Math., 25, 1893-4, 302-3. Cf. Voronoi."'

254 History of the Theory of Numbers. [Chap, viii

If 4r^ — 27s^ is a quadratic non-residue of p, the congruence has one and
only one root; but if it is a residue, there are three roots or no root.

G. Cordone^^^ gave simpler proofs of Oltramare's^^^ theorem II on the
case fjL = Qn — I, gave theorems to replace VII and VIII, and proved that the
condition in IX is sufficient as well as necessary.

Ivar Damm^^ found when Cardan's formula gives three real roots, one
or no real root of a cubic congruence, and expressed the roots by use of
his quasi sine and cosine functions. For the prime modulus p = 3nH-l,
f=x^-\-ax-\-b is irreducible if

c =

^isrea.,(-|+cf.*l.

If p = 3n — 1, it is irreducible if c and ( — 6/2+0)" are both imaginary.
There are given (p. 52) explicit expressions for h such that / is irreducible.

J. Iwanow^^ gave another proof of the theorem of Woronoj.^^^

Woronoj ^^^ gave another proof of the same theorem and stated that the
congruence has the same number of roots for all primes representable by
a binary quadratic form whose determinant equals — 4r^+27s^.

G. Arnoux^^*^ gave double-entry tables of the roots of the congruences
x''+6x*+a=0 (mod m), and solved numerical cubic congruences by in-
terpreting Cardan's formulas.

G. Arnoux^^^ treated x^+6x+a=0 (mod m) by use of Cardan's formula.
For m = 1 1 , he gave a table of the real roots for a ^ 10, 6^ 10, and the residues
of

^-4+27

When R is a quadratic residue, the cube roots of — a/2=t y/R are found by
use of a table for the Galois field of order 11^ defined by r=2 (mod 11),
and the cubic is seen to have a real and two imaginary roots involving i.
If jR is a quadratic non-residue, there are three real roots or none. Like
results are said to hold when m — 1 is not divisible by 3. If w= 1 (mod 3),
there is a single real root if 7? is a quadratic non-residue ; three real or three
imaginary roots of the third order if ^ is a residue.

L. E. Dickson'^^ proved that, if p is a prime >3, x^-\-^x-\-b=0 (mod p)
has no integral root if and only if —4/3^ — 276^ is a quadratic residue of p^
say =81)u^, and if §( — 6+/xV — 3) is not congruent to the cube of any
y+zy/ — 3, where y and z are integers. The reducible and irreducible
cubic congruences are given explicitly. Necessary and sufficient conditions
for the irreducibility of a quartic congruence are proved.

'"Rendiconti Circolo Mat. di Palermo, 9, 1895, 221-36.

"^BuU. Ac. Sc. St. Petersburg, 5, 1896, 137-142 (in Russian).

'^Natural Sc. (Russian), 10, 1898, 329; of. Fortschritte Math., 29, 1898, 156.

'3« Assoc, franc;, av. sc, 30, 1901, II, 31-50, 51-73; corrections, 31, 1902, II, 202.

'"Assoc, frang. av. sc, 33, 1904, 199-230 [182-199], and Amoux'", 166-202.

'"BuU. Amer. Math. Soc, 13, 1906, 1-8.

Chap. VIII] CUBIC CONGRUENCES. 255

D. Mirimanoff^^^ noted that the results by Arnoux"^'^" may be com-
bined by use of the discriminant D= —4b^ — 27a^= —3-Q^R in place of R,
since — 3 is a quadratic residue of a prime p = Sk-{-l, non-residue ofp = Sk — l,
and we obtain the result as stated by Voronoi.-^^^

To find which of the values 1 or 3 is taken by v when D is a quadratic
residue, apply the theorem that if /(x) = 0 (mod p) is an irreducible con-
gruence of degree n and if Xq is one of its imaginary roots (say one of the
roots of the equation f{x) = 0) , the roots are

p pn—l

Hence a function unaltered by the cycHc substitution (xqXi. . .Xn-i) has
an integral value modulo p. Take w = 3, D=d^, a a root 5^1 of 2^=1
(mod p), and let

M = (xo+aXi+a^X2)^.

If p=l (mod 3), a is an integer, and M is an integer if ^^ = 1, while M is
the cube of an integer if v = S. Thus we have Arnoux's criterion :^^^ v = S
if ilf or-| ( — 9a+V — 3d) is a cubic residue modulo p. If p= —1 (mod 3)
J/ = 3 if and only if ilf^^l (mod p), where k = {p'^ -l)/3.

For quartic congruences, we can use (a^o — a:i-|-a:2 — a^s)^.

R. D. von Sterneck^"*" noted that if p is a prime >3 not dividing A,
and if k = SAC — B^^O (mod p), then the number of incongruent values
taken by Ax^+Bx^+Cx-\-D is i{2p+(-3/p)j ; but, if k=0, the number
is p if p = Sn — l, (p+2)/3 if p = 3n+l. Generalization by Kantor.^^^

C. Cailler^^^ treated x^+px-\-q=0 (mod I), where I is a prime >3. By
the algebraic method leading to Cardan's formula, we write the congruence
in the form

(1) x^-Sabx+abia+b)^0 (mod /),

where a, h are the roots of z^-{-Sqz/p—p/S=0 (mod T), whence

z={xQ-\-aXi+ a^X2) V (9p) , a^ + a + 1 = 0 (mod I) .

Let A = 4p^+27g^. If 3A is a quadratic residue of i, a and b are distinct
and real. If 3A is a non-residue, a and b are Galois imaginaries r±s\/iV^
where N is any non-residue. For a root a: of (1),

Use is made of a recurring series S with the scale of relation [a +6, —ab]
to get 2/0, Vi,.. .. Write Q = (3A/Z). If ; = 3m-l, Q = l, then

If l = 3m-\-l, Q = l, the congruence is possible only when the real number
a/b is a cubic residue, i. e., if 2/^=0 in S; let a/b belong to the exponent
3m=f1 modulo I, whence

'"L'enseignement math., 9, 1907, 381-4.

"oSitzungsber. Ak. Wiss. Wien (Math.), 116, 1907, Ila, 895-904.

"'L'enseignement math., 10, 1908, 474r-487.

256 History of the Theory of Numbers. [Chap, viii

w= I 7 I J x= or >

\o/ 2/2^-1 2/m

according as the upper or lower sign holds. If l==Sm-\-l, Q= —1, then
2/3m+2=0, (rl =-, realx=-; .

\0/ 0 y2m+l

li l = Sm — l, Q= —1, there are three real roots if and only if a/b is a cubic
residue of I, viz., 2/^=0; when real, the roots may be found as in the second
case.

Cailler^^^ noted that a cubic equation X = 0 has its roots expressible
rationally in one root and VA, where A is the discriminant (Serret's
Algebre, ed. 5, vol. 2, 466-8). Hence, if p is a prime, X=0 (mod p) has
three real roots if one, when and only when A is a quadratic residue of p.
If p = 9m^l, his^^^ test shows that x^ — 3xH-l = 0 (mod p) has three real
roots, but no real root for other prime moduli 5^3. The function
F{x) =x^-{-x- — 2x — l for the three periods of the seventh roots of unity is
divisible by the primes 7m=*= 1 (then 3 real roots, Gauss®", p. 624) and 7,
but by no other primes.

E. B. Escott"^ noted that the equation F(x) =0 last mentioned has the
roots a, ^ = a^—2, 7=/3^— 2, so that F{x) = 0 (mod p) has three real roots
if one real root. To find the most general irreducible cubic equation with
roots a, (3, y such that

^=/(a), y=m, a=f{y),

we may assume that/(x) is of degree 2. For /(a) = a^—n, we get

(2) x^-\-ax'^-{a'-2a-\-3)x-ia^-2a^-\-da-l)=0,

with ^ = a^ — c, y=j3^—c, a=y^—c, c = o^ — a+2. The corresponding con-
gruence has three real roots if one. To treat/(a)=a^+^a+Z, add k/2 to
each root. For the new roots, jS' = a'^ — n, as in the former case. To treat
/(a) = ta^-\-ga-\-h, the products of the roots by t satisfy the preceding relation.
L. E. Dickson^^ determined the values of a for which the congruence
corresponding to (2) has three integral roots. Replace x by z—a; we get

z^-2az^+{2a-S)z-\-l = 0 (mod p).

If one root is z, the others are 1 — 1/z and 1/(1—2). Evidently a is rational
in z. If —3 is a quadratic non-residue of p, there are exactly (p — 2)/S
values of a for which the congruence has three distinct integral roots. If
— 3 is a residue, the number is (pH-2)/3. A second method, yielding an
explicit congruence for these values of a, is a direct application of his^^®
general criteria for the nature of the roots of a cubic congruence.

T. Hayashi^^^ treated cyclotomic cubic equations with three real roots
by use of Escott's^'*^ results.

"«L'interm^diaire des math., 16, 1909, 185-7. '"/bid., (2), 12, 1910-11, 149-152.

'"Annals of Math., (2), 11, 1909-10, 86-92. >«/6id., 189-192.

Chap. VIII] MISCELLANEOUS RESULTS ON CONGRUENCES. 257

Miscellaneous Results on Congruences.

Linear congruences will be treated in Vol. 2 under linear diophantine
equations, quadratic congruences in two or more variables, under sums of
four squares; ax''+hy''-}-cz''=0, under Fermat's last theorem.

Fermat^^^ stated that not every prime p divides one of the numbers
a+1, a^+l,a^+l,. . .. For, if /c is the least value for which a^' — 1 is divis-
ible by p and if k is odd, no term a^-{-l is divisible by p. But if k is even,
^fc/2_|_2 jg divisible by p.

Fermat^^^ stated that no prime 12n±l divides S'^+l, every prime
12n=t5 divides certain S'^+l, no prime 10n±l divides 5""+!, every prime
lOn^S divides certain 5"^+!, and intimated that he possessed a rule relating
to all primes. See Lipschitz.^^*^

A. M. Legendre^^° obtained from a given congruence x"=ax'*~^+- ■ •
(mod p), p SiTi odd prime, one having the same roots, but with no double
roots. Express x^^"^'^^ in terms of the powers of a; with exponents <n, and
equate the result to +1 and to —1 in turn. The g. c. d. of each and the
given congruence is the required congruence. An exception arises if the
proposed congruence is satisfied by 0, 1, . . ., p — 1.

Hoen4 de Wronski^^^ developed {ni-\- . . .-\-nJ"', replaced each multi-
nomial coefficient by unity, and denoted the result by A[ni+ . . .+nj\"*.
Thus A[ni+n2f = ni^+nin2+n2^. SetiV„ = ni+ . . . +n„. Then (pp.65-9),

(1) A[N^-nX-A[N^-nX={n,-n,)A[NT~'=0 (mod n,-n,).

Let (ni. . .nS)m be the sum of the products of ni,. . ., n„ taken m at a
time. Then (p. 143), if A[Nj' = l,

(2) A[NJ={n,.. .nJ,A[N^Y-'-in,.. .nJ^AWJ-'

+ in,.. .n^)sA[NJ-'- . . .+{-iy+\n,. . .nJ),A[Nj.

He discussed (pp. 146-151) in an obscure manner the solution of Xi=X2
(mod X), where the X's are polynomials in ^ of degree v. Set N^ = ni-\- . . .
H-n„_2+np+ng. Let the negatives of Ui,..., n„_2, Up be the roots of
P = Po-\-PiX+ . . .+P^^2^"~^-\-x"~^ = 0; the negatives of ni,..., n^-2, "riq
the roots of Q = Qo+ . . .+x"~^ = 0. We may add fiX and ^2^ to the
members of our congruence. It is stated that the new first member may
be taken to be A[A^„— nj"", whence by (2)

X,-\-^,X = P^_2A[N^-nr-'-P.-3A[N^-nX-^+ . . .,

and the A's may be expressed in terms of the P's by (2). Similarly,
^2+^2^ niay be expressed in terms of the Q's. By (1), X = nq—np = Q^_2
— P„_2. Since P = 0, Q = 0 have co — 2 roots in common, we have further
conditions on the coefficients Pi, Qi. It is argued that w — 3 of the latter

"^Oeuvres, 2, 209, letter to Frenicle, Oct. 18, 1640,
i^Oeuvres, 2, 220, letter to Mersenne, June 15, 1641.
i"M6m._Ac. Sc. Paris, 1785, 483.

"^Introduction a la Philosophic des Math^matiques et Technie de I'Argorithmie, Paris, 1811.
He used the Hebrew aleph for the A of this report. Cf. Wronski^^' of Ch. VII.

258 History of the Theory of Numbers. [Chap, viil

remain arbitrary, and that ^ is a function of them and one of the n's, which
has an arbitrary rational value.

A. Cauchy^" noted that if / and F are polynomials in x, Lagrange's
interpolation formula leads to polynomials u and v such that uJ-\-vF = R,
where i? is a constant [provided / and F have no common factor]. If the
coefficients are all integers, R is an integer. Hence R is the greatest of the
integers di\-iding both / and F. For /= x^—x, we may express i2 as a prod-
uct of trigonometric functions. If also F{x)= (x"+l)/(a:+l), where n and
p are primes, R=0 or ±2 according as p is or is not of the form nx-\-\.
Hence the latter primes are the only ones dividing x^+l, but not x-\-\.

Cauchy^^^ proved that a congruence /(x) = 0 (mod p) of degree m<p is
equivalent to (x— r)'</)(x) = 0, where 4> is of degree m—i, if and only if

/(r)^0, /'(r) = 0,. . ., r-'\r)^Q (mod p),

where p is a prime. The theorem fails if m'^p. He gave the method of
Libri (M^moires, I) for solving the problem: Given"/(a:) = 0 (mod p) of
degree m^p and with exactly m roots, and/i(x) of degree l^m, to find a
polynomial </)(a;), also with integral coeflficients, whose roots are the roots
common to/ and /i. He gave the usual theorem on the number of roots of
a binomial congruence and noted conditions that a quartic congruence have
four roots.

Cauchy^^ stated that if 7 is an arbitrary modulus and if ri, . . ., r„, are
roots of /(x)=0 (mod 7) such that each difference Vi—Tj is prime to 7, then

f{x)={x-ri) . . .(x-rJQ(x) (mod 7).

If in addition, m exceeds the degree of /(x), then/(x) = 0 (mod 7) for every x.
A congruence of degree n modulo p^, where p is a prime, has at most n
roots unless every integer is a root. If /(r) = 0 (mod 7) and if in the irre-
ducible fraction equal to

_/(r)

the denominator is prime to 7, then r— r7 is a root of /(a:)=0 (mod P).

V. A. Lebesgue^^^ wrote a/b=c (mod p) if h is prime to p and a=bc
(mod p), and a/b=c/d (mod p) \i h, d are prime to p and ad=bc (mod p).

J. A. Serret^^^ stated and A. Genocchi proved that, if p is a prime, the
sum of the mth. powers of the p" polynomials in x, of degree n — 1 and with
integral coefficients <p, is a multiple of p if m<p'' — 1, but not if m = p'' — 1.

J. A. Serret^^^ noted that all the real roots of a congruence f{x) = 0
(mod p), where p is a prime, satisfy \j/{x)^0, where \f/ is the g. c. d. of f{x)
andxP~^-l.

'"Exercices de Math., 1, 1826, 160-6; Bull. Soc. Philomatique; Oeuvres, (2), 6, 202-8.

^"Exercices de Math., 4, 1829, 253-279; Oeuvres, (2), 9, 298-326. j

i"Compte8 Rendus Paris, 25, 1847, 37; Oeuvres, (1), 10, 324-30. ~\

'"Nouv. Ann. Math., 9, 1850, 436.

i^Nouv. Ann. Math., 13. 1854, 314; 14, 1855, 241-5

"'Cours d'alg^bre sup6rieure, ed. 2, 1854, 321-3.

Chap. VIII] MISCELLANEOUS RESULTS ON CONGRUENCES. 259

N. H. AbeP^^ proved that we can solve by radicals any abelian equation,
i. e., one whose roots are r, 0(r), 0^(r) = <t)[<i){r)], . . ., where </> is a rational
function. H. J. S. Smith^^^ concluded that when the roots of a congru-
ence can be similarly expressed modulo p, its solution can evidently be
reduced to the solution of binomial congruences, and the expressions for
the roots of the corresponding equation may be interpreted as the roots
of the congruence. For the special case a:"=l, this was done by Poinsot
in 1813-20 in papers discussed in the chapter on primitive roots.

M. Jenkins^^^" noted that all solutions of a^=l(mod x) are x= Un=UiU2
. . .Un, where Ui is any divisor of any power of a — 1; u^ any divisor prime
to a — 1, of any power of a'" — 1;. . .; u,, any divisor, prime to a^"-2 — 1,
of any power of a^^-'^ — l. For a*+l = 0 (mod x), modify the preceding
by taking odd factors of a+1 instead of factors of a — 1.

J. J. Sylvester^®° proved that if p is a prime and the congruence /(a:) = 0
(mod p) of degree n has n real roots and if the resultant of f{x) and g{x)
is divisible by p, then g{x)^0 has at least one root in common with /(a;) = 0.
There are exactly p — 1 real roots of x^~^=l (mod p^).

A. S. Hathaway^^^ noted the known similarity between equations and
congruences for a prime modulus. He^^^ made abstruse remarks on higher
congruences.

G. Frattini^^^ proved that x^ — Dy'^=\ and x'^ — Dy^=\ are each solvable
when the modulus is a prime p>5 and Dp^O. If d = B^—AC^O, then
Ax'^-i-2Bx^y+Cy"=\ (mod p) is solvable since dx'^+XC can be made con-
gruent to a square and hence to {Cy-{-Bx^y. Likewise for ax'^-\-2bx-\-c=y'^.

A. Hurwitz^^^ discussed the congruence of fractions and the theory of
the congruence of infinite series. If (/)(x) =ro-\-riX-{- . . . +r„a:V^-+ • • • and
if yp{x) is a similar series with the coefficients s^, then 0 and \l/ are called
congruent modulo m if and only if Vn^s^ (mod m) for n = 1, 2, . . . .

G. Cordone^^^ treated the general quartic congruence for a prime
modulus ji by means of a cubic resolvent. The method is similar to Euler's
solution of a quartic equation as presented by Giudice in Peano's Rivista
di Matematica, vol. 2. For the special case x'^-\-%Hx^-\-K=0 (mod /x),
set t = {ix — l)/2, r^ = 9H^ — K; then if K is a quadratic residue of /jl, there
are four rational roots or none according as ( — 3/f+r)'=+l or not; but
if K is a non-residue, there are two rational roots or none according as one
of the congruences

(-3H+r)'=4-l, i-ZH-ry^-l

is satisfied or not.

i^sjour. fur Math., 4, 1829, 131; Oeuvres, 1, 114.

"sReport British Assoc. 1860, 120 seq., §66: Coll. M. Papers, 1, 141-5.

"9aMath. Quest. Educ. Times, 6, 1866, 91-3.

""Amer. Jour. Math., 2, 1879, 360-1; Johns Hopkins University Circulars, 1, 1881, 131. Coll.

Papers, 3, 320-1.
i"Johns Hopkins Univ. Circulars, 1, 1881, 97. "^Amer. Jour. Math., 6, 1884, 316-330.

"^Rendiconti Reale Accad. Lincei, Rome, (4), 1, 1885, 140-2.
i"Acta Mathematica, 19, 1895, 356.
«6Rendiconti Circolo Mat. di Palermo 9, 1895, 209-243.

260 History of the Theory of Numbers. [Chap, viii

R. Lipschitz^^^ examined Fermat's^^^ statement and proved that the
primes p for which a' +1 = 0 (mod p) is impossible are those and only those
for which a solution u of w" =a (mod p) is a quadratic non-residue of p
and for which X^A.', where 2^ is the highest power of 2 dividing p — 1.
Cases when a''+l = 0 is impossible and not embraced by Fermat's rule are
a = 2, p = 89, 337; a = S, p = 13; a=-2, p = 281; etc.

L. Kronecker^^^ called /(.r) an invariant of the congruence k=k' (mod m),
if the latter congruence implies the equality /(/v) =/(//). If also, conversely,
the equality implies the congruence, f{x) is called a proper (or characteristic)
invariant, an example being the least positive residue of an integer modulo
m. It is shown that every invariant of k=k' (mod m) can be represented
as a symmetric function of all the integers congruent to k modulo m.

G. Wertheim^^^ proved that a^+l = 0 (mod p) is impossible if a belongs
to an odd exponent modulo p [Fermat^'^^].

E. L. Bunitzky^*^^ (Bunickij) noted that, for any integer M, the con-
gruences

f(a+kh)=rk (mod M) (A: = 0, 1,. . ., n)

hold if and only if the coefficients Ak of /(x) satisfy the conditions
k\h''Ak=A% (mod M) {k = 1, . . . , n).

If k is the least value of x for which xlh"" is divisible by M, and if the
g. c. d. of M and h is k<m, where m is a divisor of M, then if /(a;)=0 (mod
M) has the roots a, a-\-h,..., a-\-{k — l)h, it has also the roots a-\-jh
{j = k,k-\-l,...,m-l).^

G. Biase^^'' called a similar to h in the ratio m:n modulo k if the remainders
on dividing a and h by k are in the ratio m:n. Two numbers similar to a
third in two given ratios modulo k are similar to each other modulo k in
a ratio equal to the quotient of the given ratios.

The problem^ '^^ to find n numbers whose n^ — n differences are incon-
gruent modulo n^ — n+1 is possible for n = 6, but not for n = 7.

R. D. von Sterneck^^° proved that, if A is not divisible by the odd
prime p, Ax'^+Bx^+C takes \p{2AB, p) incongruent values (when x ranges
over the set 0, 1, . . ., p — 1) if 5 is not divisible by p, while if B is divisible
by p, it takes (p+3)/4 or (p-fl)/2 values according as p = 4n-l-l or p =
471 — 1. In terms of Legendre's symbol,

>««Bull. des Sc. Math., (2), 22, I, 1898, 123-8. Extract in Oeuvres de Fermat, 4, 196-7.

>"Vorlesungen iiber Zahlcntheorie, I, 1901, 131-142.

"^AnfangsRTunde der Zahlenlehre, 1902, 265.

''"Zap. mat. otd. Obsc. (Soc. of natur.), Odessa, 20, 1902, III- VIII (in Russian); cf. Fortschr.

Math., 33, 1902, p. 205.
•^"Il Boll. Matematica Gior. Sc. Didat., Bologna, 4, 1905, 96.
i"L'interm6diaire des math., 1906, 141; 1908, 64; 19, 1912, 130-1. Amcr. Math. Monthly, 13,

1906, 215; 14, 1907, 107-8.

Chap. VIII] MISCELLANEOUS RESULTS ON CONGEUENCES. 261

E. Landau^'^ proved that, if /(x) =0 is an equation with integral coeffi-
cients and at least one root of odd multiplicity, there exist an infinitude of
primes p = 4:n — l such that /(a;) = 0 (mod p) has a root.

R. D. von Sterneck^^^ found the number of combinations of the ith. class
(with or without repetition) of the numbers prime to p of a complete set of
residues modulo p^ whose sum is congruent to a given integer modulo p^,
p being a prime.

E. Piccioli^^'* gave known theorems on adding and multiplying con-
gruences.

C. Jordan^^^ found the number of sets of integers aik for which the
determinant |aa-| of order n is congruent to a given integer modulo M.

C. Krediet^^^ gave theorems on congruences of degree n for a prime
modulus analogous to those for an algebraic equation of degree n, including
the question of multiple roots. The determination of roots is often sim-
plified by seeking first the roots which are quadratic residues and then
those which are non-residues. The exposition is not clear or simple.

G. Rados"^ proved that, if p is a prime,

fix) = ao^^-^+ • • ■ +«p-2= 0, g{x) = hx^'-^-i- . . . +bp_2= 0 (mod p)

have a common root if and only if each Ri=0 (mod p), where

*(w) =Rou''-^+Riu''-^-\- . . . +Rp-i

aou+bo aiU+bi ... ap_2W+6p_2

aiu+bi a2U-\-b2 . . . aoU-{-bo

ap_2U+bp-2 aou+bo ... ttp-s^+^p-s

For ^=/', let ^(u) become DoU^~^-\- . . . +i)p_2; thus/(a:)^0 (mod p) has a
multiple root if and only if each A=0 (mod p). Each of these theorems
is extended to three congruences. Finally, if f(x) and f'(x) are relatively
prime algebraically, there is only a finite number of primes p for which the
number of roots of /= 0 (mod p'') exceeds the degree of /.

G. Frattini^^^ proved that if p and q are primes, q a divisor of p — 1,
every homogeneous symmetric congruence in q variables is solvable modulo
p by values of the variables distinct from each other and from zero except
when the degree of the congruence is divisible by q.

C. Grotzsch^'^ noted that if a is a root of a^'^^a (mod p), where a is prime
to p, then x=a (mod p^ — p) is a root, and proved that if d is the g. c. d. of
ind a and p — 1 and if ind a>0, it has exactly

^''^Handbuch . . .Verteilung der Primzahlen, 1, 1909, 440.
^"Sitzungsber. Ak. Wiss. Wien (Math.), 118, 1909, Ila, 119-132.
'^"11 Pitagora, Palermo, 16, 1909-10, 125-7.
"5Jour. de Math., (6), 7, 1911, 409-416.
'^^Wiskundig Tijdschrift, Haarlem, 7, 1911, 193-202 (Dutch).
i"Ami. sc. ecole norm, sup., (3), 30, 1913, 395-412.
"speriodico di Mat., 29, 1913, 49-53.
"'Archiv Math. Phys., (3), 22, 1914, 49-53.

262 History of the Theory of Numbers. [Chap, viii

iV = 0(p-l)+2^^)

roots incongruent modulo p(p — 1), where 5 ranges over all divisors > 1 of ^.
If ind a = 0, the number of such roots is p — l-\-N, where now 5 ranges over
the di\asors >1 of p — 1.

A. Chdtelet^^° noted that divergences between congruences and equa-
tions are removed by not Umiting attention to the given congruence fix) = 0
of degree n, but considering simultaneously all the polynomials g{x) derived
from f{x) by a Tschirnhausen transformation ky — (i>{x), where k is an
integer and </> has integral coefficients and is of degree n — 1.

*M. Tihanyi^^"" proved a simple congruence.

R. Kantor^^^ discussed the number of incongruent values modulo m

taken by a polynomial in n variables, and especially for ax^-\- . . .+d

modulo p', generalizing von Sterneck.^"*"

The solvabiUty of x^+9a;+6=0 and x^-\-y{y-\-l) = 0 (mod p) has been
treated.^«2

A. Cunningham^^ announced the completion, in conjunction with
Woodall and Creak, of tables of least solutions {x, a) of the congruences

T^=^y% rV==*=l (mod p*< 10000), r = 2, 10; ?/ = 3, 5, 7, 11.

T. A. Pierce^^^ gave two proofs that /(a;) = 0 (mod p) has a real root if
and only if the odd prime p divides 11(1— a^^"^), where a^ ranges over the
roots of the equation f{x) = 0.

Christie^^ stated that P(F+1) = 1 (mod p) if t= 2 sin 18° and p is any
odd prime. Cunningham gave a proof and a generalization.

*G. Rados^^^ found the congruence of degree r having as its roots the
r distinct roots ?^0 of a given congruence of degree p — 2 modulo p, a
prime.

i8'€omptes Rendus Paris, 158, 1914, 250-3.

"""Math, es Phys. Lapok, Budapest, 23, 1914, 57-60.

i8iMonatshefte Math. Phys., 26, 1915, 24-39. J

'»2Wiskundige Opgaven, 12, 1915, 211-2, 215-7.

'"Messenger Math., 45, 1915-6, 69.

'"Annals of Math., (2), 18, 1916, 53-64.

i«*Math. Quest. Educ. Times, 71, 1899, 82-3.

'»Math. is Term6s firtesito, 33, 1915, 702-10.

CHAPTER IX.

DIVISIBILITY OF FACTORIALS AND MULTINOMIAL COEFFICIENTS.
Highest Power of a Prime Dividing ml

Genty^ noted that the highest power of 2 dividing (2'*) ! is 2^""^ and the
quotient is 3"-'(5-7)"-2(9-lM3-15)"-^(17. . .31)""^ . .(2"-l). In general
if P = 2"'+2"'+. . .+2% where the n's decrease, the highest power of 2
dividing P! is 2^-^

A. M. Legendre^ proved that if p" is the highest power of the prime p
which divides m !, and if [x] denotes the greatest integer ^ x,

where s = ao+ • • • +«« is the sum of the digits of m to the base p:

Th. Bertram^ stated Legendre's result in an equivalent form.
H. Anton* proved that, U n = vp+a, a<p, v<p, and p is a prime,

= (p — l)'a!y! (mod p),

n!

P

while, if v = vp-\-a, a'<p, v'<p,

■^,= {p-iy+^'a\a\v\v\ (modp).

D. Andr^^ stated that the highest power p" of the prime p dividing n!
is given expHcitly by }i=^lZi[n/p^] and claimed that merely the method of
finding ii had been given earHer. He appHed this result to prove that the
product of n consecutive integers is divisible by n!.

J. Neuberg*' determined the least integer m such that m\ is divisible by
a given power of a prime, but overlooked exceptional cases.

L. Stickelberger^ and K. HenseP gave the formula [cf. Anton*].

(2) ^^(-irao!ai!...aj(modp).

F. de Brun^ wrote g[u] for the exponent of the highest power of the
prime p dividing u. He gave expressions for

■^ rP{n;k)=Uf\ g[rP(n;k)]

3 = 1

in terms of the functions h{a; k) = l*+2*-f . . . +a^. A special case gives (1).

^Hist. et M6m. Ac. R. Sc. Inscript. et Belles Lettres de Toulouse, 3, 1788, 97-101 (read Dec. 4,

1783).
''Th^orie des nombres, ed. 2, 1808, p. 8; ed. 3, 1830, I, p. 10.
'Einige Satze aus der Zahlenlehre, Progr. Coin, Berlin, 1849, 18 pp.
*Archiv Math. Phys., 49, 1869, 298-9.
"Nouv. Ann. Math., (2), 13, 1874, 185.

^Mathesis, 7, 1887, 68-69. Cf. A. J. Kempner, Amer. Math, Monthly, 25, 1918, 204-10.
'Math. Annalen, 37, 1890, 321.
sArchiv Math. Phys., (3), 2, 1902, 294.
»Arkiv for Matematik, Astr., Fysik, 5, 1904, No. 25 (French).

263

264 History of the Theory of Numbers. [Chap, ix

R. D. CarmichaeP" treated the problem to find m, given the prime p
and s = ^ai, in Legendre's formula; a given solution m-, leads to an infinitude
of solutions m-zv'', k arbitrary. Again, to find 771 such that p"*~' is the highest
power of p>2 dividing m\, we have m — t={m — s)/{p — l), and see that m
has a hmited number of values; there is always at least one solution m.

Carmichael" used the notation H\y\ for the index of the highest power
of the prime p dividing y, and evaluated

;i=i/{n(xa+c)|,

where a, c are relatively prime positive integers. Set Co = c and let % be
the least integer such that iVa+Cr-i is divisible by p, the quotient being Cr.
Let

ei

= [^4^']' ^'=[^]' ^>i-

t-i
Then /i= 2(6^+1), where t is the least subscript for which

r=l

Ct{a-\-Ct){2a-^Ct) . . . (cta+Ct)
is not divisible by p. It follows that

where R is the index of the highest power of p not exceeding 7i — 1 . If n is a
power of p, /i = (n — l)/(p — 1). But if n = 8kp''-\- . . .-\-dip-\-8o, 8k9^0, and
at least one further 8 is not zero,

^SftSfc+^. <r = 6.+ ...+6o.

P — 1 p — 1

In case the first x for which xa-\-c is divisible by p gives c as the quotient,
all the Cr are equal and hence all the v; then

, _ rn — 1—i+pl . rn — l—i — ip-\-p^l , rn — l—i — ip — ip'^-i-p^l .

L p J"^L p' J"^L w J"^'"

The case a = c = l yields Legendre's^ result. The case a = 2, c = 1, gives

Hll.3.5. . .(2„-l)( = [?^^] + [?^^^>. . ..

E. Stridsberg^^ wrote H^ for (1) and considered

Trt = a{a-\-m) . . .{a-{-'mt),

where a is any integer not divisible by the positive integer m. Let p be a
prime not dividing m. Write a^ for the residue of aj modulo m. He noted
that, if pj=l (mod m),

"BuU. Amer. Math. Soc, 14, 1907-8, 74-77; Amer. Math. Monthly, 15, 1908, 15-17.

''Ibid., 15, 1908-9, 217.

"Arkiv for Matematik, Astr., Fysik, 6, 1911, No. 34.

1

Chap. IX] DIVISIBILITY OF FACTORIALS, MULTINOMIAL COEFFICIENTS. 265

is an integer, and wrote L^ for its residue modulo p^+\ Set

:.= P

He proved that tt^ is divisible by p*, where s = Hi+Sj;io2^. If t„ is the
first one of the numbers tq, ti, . . . which is <p — 1, tt^ is divisible by p",

k

A. Cunningham^^ proved that if / is the highest power of the prime z
dividing p, the number of times p is a factor of p"! is the least of the
numbers ^„ 2^«-^+i-l

for the various primes z dividing p.

W. Janichen^^ stated and G. Szego proved that

i:tx{n/d)v{d)=ci>{n)/{v-l),

summed for the divisors d of n, where v{d) is the exponent of the highest
power of p (a prime factor of n) which divides d\, for /x as in Ch. XIX.

Integral Quotients Involving Factorials.

Th. Schonemann^^ proved, by use of symmetric functions of pth roots
of unity, that if b is the g. c. d. of fjL,v,'...,
8-{m-l)l

.ii/l

= integer, {m—fx+v-\- . . .).

fJLlVl

He gave (p. 289) an arithmetical proof by showing that the fractions
obtained by replacing 8 by fi, v, .. . are integers.
A. Cauchy^^ proved the last theorem and that

^ -^ ^ = integer, {m = a-\- . . .+k).

a\. . .k\

D. Andre^*^ noted that, except when n = l, a = 4, n(n + l). . .(na — 1) is
not or is divisible by a" according as a is a prime or not.

E. Catalan^^ found by use of elliptic functions that

{m-\-n-\)\ (2m) ! (2n) !

m!n! m\n\{m-\-n)\

are integers, provided m, n are relatively prime in the first fraction.

^^L'intermediaire des math., 19, 1912, 283-5. Text modified at suggestion of E. Maillet.

"Archiv Math. Phys., (3), 13, 1908, 361; 24, 1916, 86-7.

»8Jour. fur Math., 19, 1839, 231-243.

"Comptes Rendus Paris, 12, 1841, 705-7; Oeuvres, (1), 6, 109.

20N0UV. Ann. Math., (2), 11, 1872, 314.

"/fttd., (2), 13, 1874, 207, 253. Arith. proofs, Amer. Math. Monthly, 18, 1911, 41-3.

266 History of the Theory of Numbers. [Chap, ix

P. Bachmann^- gave arithmetical proofs of Catalan's results.

D. Andr^-^ proved that, if aj, . . . , a„ have the sum N and if k of the a's
are not di\isible by the integer >1 which divides the greatest number of
the a's, then (iV— A;)! is di\'isible by ai!. . .a„!.

J. Bourguet^^ proved that, if k^2,

{kmi)l ikmo)\...{knh)\

— , . ^ , ; r: = mteger.

Wi!. . .nikl (wi+. . .+mk)l

M. WeilP^ proved that the multinomial coefficient (tq) ! -r- {q\y is divisible
by tl

WeilP^ stated that the following expression is an integer :

(a+i8+ ■ • ■ +pg+Pigi+ ■ ■ • +rst) !
am. . .{piyq\{p,\y^q,\. . .{r\ns\yt\'

WeilP^ stated the special case that {a-\-^-\-pq-\-rs)\ is divisible by
a\^\{q\rp\{s\yrl

D. Andr^-^ proved that (tq) ! -r- (g!)' is divisible by (<!)* if for every prime
p the sum of the digits of q to base p is ^k.

Ch. Hermite'^^ proved that n! divides

m{7n+k){m+2k) . . . lm+{n-l)k]k''-\

C. de PoUgnac^" gave a simple proof of the theorem by WeilP^ and
expressed the generalization by Andr^^^ in another and more general form.

E. Catalan^^ noted that, if s is the number of powers of 2 having the sum

^+^' (2a)! (26)!

a!6!(a+6)!
is an even integer and the product of 2' by an odd number.
E. Catalan^^ noted that, if n = a+6+ . . . -{-t,

n\{n+t)
a\h\...tl

is divisible by a+t, h+t,. . ., a-\-h-\-t,. . ., a-\-b+c+t,. . ..

E. Ces^ro^^ stated and Neuberg proved that (p) is divisible by n(n — 1)
if p is prime to n(n — 1), and p — l prime to n — 1; and divisible by (p + 1)
X(p+2) if p-\-l is prime to n+1, and p+2 is prime to (n + l)(n+2).

"Zeitschrift Math. Phys., 20, 1875, 161-3. Die Elemente der Zahlentheorie, 1892, 37-39.
«Bull. Soc. Math. France, 1, 1875, 84.

"Nouv. Ann. Math., (2), 14, 1875, 89; he wrote r(n) incorrectly for n!; see p. 179.
'MDomptes Rendus Paris, 93, 1881, 1066; Mathesis, 2, 1882, 48; 4, 1884, 20; Lucas, Th^orie

des nombres, 1891, 365, ex. 3. Proof by induction, Amer. M. Monthly, 17, 1910, 147.
»«Bull. Soc. Math. France, 9, 1880-1, 172. Special case, Amer. M. Monthly, 23, 1916, 352-3.
"Mathesis, 2, 1882, 48; proof by Li6nard, 4, 1884, 20-23.
"Comptes Rendus Paris, 94, 1882, 426.
"Faculty des Sc. de Paris, Cours de Hermite, 1882, 138; ed. 3, 1887, 175; ed. 4, 1891, 196.

Cf. Catalan, M6m. Soc. Sc. de Li6ge, (2), 13, 1886, 262-^ ( = Melanges Math.); Heine.""
»"Comptes Rendus Paris, 96, 1883, 485-7. Cf . Bachmann, Niedere Zahlentheorie, 1, 1902. 59-62.
«Atti Accad. Pont. Nouvi Lincei, 37, 1883-4, 110-3.
"Mathesis, 3, 1883, 48; proof by Cesiro, p. 118.
"Ibid., 5, 1885, 84.

Chap. IX] DIVISIBILITY OF FACTORIALS, MULTINOMIAL COEFFICIENTS. 267

E. Catalan^^ noted that

e::r)'(?)"*e)-«"

F. Gomes Teixeira^^ discussed the result due to Weill. ^®
De Presle^® proved that

{k-\-l)(k+2)...{k+hl) . ^

nw ^ ^^ ^^^''

being the product of an evident integer by {hl)\/{U{h\y}. ,

E. Catalan^^ noted that, if n is prime to 6,

(2n-4)!

nl{n-2)\
H. W. Lloyd Tanner^^ proved that

= integer.

= integer.

{\,\...\,\ng\y

L. Gegenbauer stated and J. A. Gmeiner^^ proved arithmetically that,
if n=Sjrja_,iaj2. • Oys, the product

m{m+k)(m-h2k) . . . {m+{n-l)k}k''-'
is divisible by

where m, k, n, an,- ■ ■, o,rs are positive integers. This gives Hermite's'^'
result by taking r = s = l. The case m = A; = l,s = 2, is included in the result
by Weill.26

Heine^^" and A. Thue^° proved that a fraction, whose denominator is k\
and whose numerator is a product of k consecutive terms of an arithmetical
progression, can always be reduced until the new denominator contains only
such primes as divide the difference of the progression [a part of Her-
mite's^^ result].

F. Rogel'*^ noted that, if P be the product of the primes between (p — 1)/2
and p + 1, while n is any integer not divisible by the prime p,

(n-l)(n-2). ..{n-p-^l)P/p=0 (mod P).
S. Pincherle^^ noted that, if n is a prime,

P={x+l){x+2) . ..(x+n-l)
is divisible by n and, if x is not divisible by n, by n !. If n = Up", P is divisible

="Nouv. Ann. Math., (3), 4, 1885, 487. Proof by Landau, (4), 1, 1901, 282.

35Archiv Math. Phys., (2), 2 1885, 265-8. ^eBuU. Soc. Math. France, 16, 1887-8, 159.

"M6m. Soc. Roy. Sc. Li^ge, (2), 15, 1888, 111 (Melanges Math. III). Mathesis, 9, 1889, 170.

"Proc. London Math. Soc, 20, 1888-9, 287. ^QMonatshefte Math. Phys., 1, 1890, 159-162.

"a Jour, fur Math., 45, 1853, 287-8. Cf. Math. Quest. Educ. Times, 56, 1892, 62-63.

"Archiv for Math, og Natur., Kristiania, 14, 1890, 247-250.

"Archiv Math. Phys., (2), 10, 1891, 93.

"Rendiconto Sess. Accad. Sc. Istituto di Bologna, 1892-3, 17.

268 History of the Theory of Numbers. [Chap, ix

by n ! if and only if divisible by IIp"'''^, where /3 is the exponent of the power
of p dividing (n — 1)!.

G. Bauer^^ proved that the multinomial coefficient (n+ni+n2+. . .)'
-7- {7i!7?i! . . . } is an integer, and is even if two or more n's are equal.

E. Landau^^ generalized most of the preceding results. For integers
Qij, bij, each ^ 0, and positive integers Xj, set

Then / is an integer if and only if

m n

t=i t=i
for all real values of the Xj for which O^Xj^l. A new example is

(4m)!(4n)! a

m!n!(2m+n)!(m+2n)!~^^^^^^' |

P. A. MacMahon^^ treated the problem to find all a's for which

is an integer for all values of n; in particular, to find those "ground forms"
from which all the forms may be generated by multiplication. For m = 2,
the ground forms have (ai, a2) = (1, 0) or (1, 1). For m = 3, the additional
ground forms are (1, 1, 1), (1, 2, 1), (1, 3, 1). For ?7i = 4, there are 3 new
ground forms; for m = 5, 13 new.

J. W. L. Glaisher^® noted that, if Bp{x) is Bernoulli's function, i. e., the
polynomial expression in x for F~^+2^"^+ . . . + (x — 1)^"^ [Bernoulli^^"''
of Ch. V],

x{x-\-l) . . .{x-\-p — l)/p=Bp{x)—x (mod p).

He gave (ibid., 33, 1901, 29) related congruences involving the left member
and Bp_i{x).

Glaisher^^ noted that, if r is not divisible by the odd prime p, and
l = kp+t, 0^t<p,

l{r+l){2r+l) . . . {(p-l)r+i)/p^-|[^]^+A:} (mod p),

where [t/p]r denotes the least positive root of px=t (mod r). The residues
mod p^ of the same product l{r-\-l) . . . are found to be complicated.

E. Maillet*^ gave a group of order t\{q\y contained in the sjrmmetric
group on tq letters, whence follows Weill's^^ result.

«SitzunKsber. Ak. Wiss. Miinchen (Math.), 24, 1894, 34&-8.

"Nouv. Ann. Math., (3), 19, 1900, 344-362, 576; (4), 1, 1901, 282; Archiv Math. Phys., (3), 1,

1901, 138. Correction, Landau."
«Trans Cambr. Phil. Soc, 18, 1900, 12-34.
"Proc. London Math. Soc, 32, 1900, 172.
^'Messenger Math., 30, 1900-1, 71-92.
*»Mem. Pr6s. Ac. Sc. Paris, (2), 32, 1902, No. 8, p. 19.

Chap. IX] DIVISIBILITY OF FACTORIALS, MULTINOMIAL COEFFICIENTS. 269

M. Jenkins^^" counted in two ways the arrangements of n = 4>f-\-'yg-\- . . .
elements in 4> cycles of / letters each, 7 cycles of g letters, . . . , where/, g, ...
are distinct integers > 1, and obtained the result

fct>\g'y\... \2\ Sr4\ ' ' ' ^^ ^ n\)'
C. de Polignac*^ investigated at length the highest power of n! dividing
(nx) \/{x\y. Let rip be the sum of the digits of n to base p. Then

{x-\-n)p = Xp+np-k{p -1) , {xn)p = Xp-np-k'{p-l),

where k is the number of units "carried" in making the addition x-\-n, and k'
the corresponding number for the multiplication x-n.

E. Sch6nbaum^° gave a simplified exposition of Landau's first paper.^^

S. K. Maitra^i proved that (n - 1) (2n - 1) . . . { (n - 2)n - 1 } is divisible by
(n — 1) ! if and only if n is a prime.

E. Stridsberg^^ gave a very elementary proof of Hermite's^^ result.

E. Landau^^ corrected an error in his^'* proof of the result in No. Ill of his
paper, no use of which had been made elsewhere.

Birkeland^^ of Ch. XI noted that a product of 2^k consecutive odd in-
tegers is^l (mod 2^).

Among the proofs that binomial coefficients are integers may be cited
those by:

G. W. Leibniz, Math. Schriften, pub. by C. I. Gerhardt, 7, 1863, 102.

B. Pascal, Oeuvres, 3, 1908, 278-282.

Gioachino Pessuti, Memorie di Mat. Soc. Italiana, 11, 1804, 446.

W. H. Miller, Jour, fiir Math., 13, 1835, 257.

S. S. Greatheed, Cambr. Math. Jour., 1, 1839, 102, 112.

Proofs that multinomial coefficients are integers were given by:

C. F. Gauss, Disq. Arith., 1801, art. 41.

Lionnet, Complement des elements d'arith., Paris, 1857, 52.
V. A. Lebesgue, Nouv. Ann. Math., (2), 1, 1862, 219, 254.

Factorials Dividing the Product of Differences of r Integers.

H. W. Segar^" noted that the product of the differences of any r distinct
integers is divisible by (r — l)!(r — 2)!. . .2!. For the special case of the
integers 1, 2, . . ., n, r+1, the theorem shows that the product of any n
consecutive integers is divisible by n!.

A. Cayley®^ used Segar's theorem to prove that

m{m — n) . . .{m — r — ln)-rf

is divisible by r! if m, n are relatively prime [a part of Hermite's-^ result].
Segar®^ gave another proof of his theorem. Applying it to the set

^8aQuar. Jour. Math., 33, 1902, 174-9. "Bull. Soc. Math. France, 32, 1904, 5-43.
"Casopis, Pras, 34, 1905, 265-300 (Bohemian).
"Math. Quest. Educat. Times, (2), 12, 1907, 84-5.

^^Acta Math., 33, 1910, 243. "Nouv. Ann. Math., (4), 13, 1913, 353-5.

soMessenger Math., 22, 1892-3, 59. "Messenger Math. 22, 1892-3, p. 186. Cf. Hermite."

^Hbid., 23, 1893-4, 31. Results cited in I'interm^diaire des math., 2, 1895, 132-3, 200; 5, 1898,
197; 8, 1901, 145.

270 History of the Theory of Numbers. [Chap, ix

a, a-\-N,. . ., a+A^", we conclude that the product of their differences is
divisible by n!(n — 1)!. . .21 = p. But the product equals

p=iN-ir-' (ir--ir-\ . .{N^-'^-iyiN"-'-!),

multiplied by a power of A^. Hence, if N is prime to n!, P is divisible by v;
in any case a least number X is found such that N^P is divisible by ;'. It is
shown that the product of the differences of mi,. . ., m^ is divisible by
k\{k — l)\. . .2! if there be any integer p such that Wi+p, . . ., nik+p are
relatively prime to each of 1, 2, . . . , A;. It is proved that the product of any
n distinct integers multiplied by the product of all their differences is a
multiple of n!(n-l)!. . .2!.

E. de Jonquieres^^ and F. J. Studnicka^ proved the last theorem.

E, B. Elliott^^ proved Segar's theorem in the form: The product of the
differences of n distinct numbers is di\'isible by the product of the differences
of 0, 1,..., n — 1. He added the new theorems: The product of the
differences of n distinct squares is divisible by the product of the differences
of 0", 1",..., (n — 1)"; that for the squares of n distinct odd numbers,
multiplied by the product of the n numbers, is divisible by the product of
the differences of the squares of the first n odd numbers, multiplied by their
product.

Residues of Multinomial Coefficients.

Leibniz^' '^ of Ch. Ill noted that the coefficients in (ZaY—Za^ are
di\'isible by p.

Ch. Babbage^^ proved that, if n is a prime, (^n-/) — 1 is divisible by
n^, while ("p") — 1 is divisible by p if and only if p is a prime.

G. Libri^'' noted that, if m = 6p-hl is a prime,

2^p-^-^ep-l-(^^P~^y+(^P~^y'- ..=0 (mod m).

E. Kummer^^ determined the highest power p^ of a prime p dividing

^; ^1 > A = ao+aip-{-. . .-{-aip\ B=ho+hip-{- . . .+bip\

where the a, and 6, belong to the set 0, 1,. . ., p — 1. We may determine
Ci in this set and e, = 0 or 1 such that

(3) ao+6o = €oP+Co, €o+ai+6i = eip+Ci, ei +a2 + ?>2 = €2^4-^2, •■ ••

Multiply the first equation by 1, the second by p, the third by p^, etc., and
add. Thus

A+B = Co-\-Cip+ . . .+Cip'+e,p'+\

"Comptes Rendus Paris, 120, 1895. 408-10. 534-7.

"Vpstnik Ceske Ak., 7, 1898, No. 3, 165 (Bohemian).

«Messinger Math., 27, 1897-8, 12-15.

"Edinburgh Phil. Jour., 1, 1819, 46.

"Jour, fur Math., 9, 1832, 73. Proofs by Stern, 12, 1834, 288.

"/6ui., 44, 1852, 115-6. Cayley, Math. Quest. Educ. Times, 10, 1868, 88-9.

Chap. IX] DIVISIBILITY OF FACTORIALS, MULTINOMIAL COEFFICIENTS. 271

Hence, by Legendre's formula (1),

ip-l)N = A-\-B-y-ei-{A-a)-{B-P), a=Sa„ ^ = 26^, 7=Sc,.
Insert the value of a+/3 obtained by adding equations (3). Thus

A. Genocchi'^^ proved that, if m is the sum of n integers a,h,...,k, each
divisible by p — l, and if m<p" — 1, then m\-i- {a\bl. . .k\} is divisible by the
prime p.

J. Wolstenholme^^ proved that f"ll) = l(mod n^) if n is a prime > 3.

H. Anton^ (303-6) proved that if n = vp+a, r = wp+h, where a, h, v, w
are all less than the prime p,

according as a^ 6 or a < 6.

M. Jenkins^^" considered for an odd prime p the sum

"^^ ^\mr+k{p-l)J'

extended over all the integers k between nr/(p — l) and —mr/{p — l), in-
clusive, and proved that (Tr=o'p (mod p) if the g. c. d. of r, p — 1 equals that
of p, p-1.

E. Catalan^^ noted that C'^_}) = l(mod p), if p is a prime.

Ch. Hermite^^ proved by use of roots of unity that the odd prime p divides

/2n+l\ , /2n+l\ , /2n+l\ ,
{p-l) + [2p-2r[sp-3r-'

E. Lucas'^^ noted that, if m = pmi-\-ii, n = pni+v, ii<p, v<p, and p is
a prime.

In general, if fxi, fJL2, ■ ■ ■ denote the residues of m and the integers contained
in the fractions m/p, m/p^, . . . , while the v's are the residues of n, [n/p], . . . ,

e)-t;)t)- '-'^^'-

E. Lucas'^'^ proved the preceding results and

0-0. f ;>(-!)". (^:>0(modp),

according as n is between 0 and p, 0 and p — l, or 1 and p.

"Nouv. Ann. Math., 14, 1855, 241-3.

"Quar. Jour. Math., 5, 1862, 35-9. For mod. w^ Math. Quest. Educ. Times, (2), 3, 1903, 33.
"'^Math. Quest. Educ. Times, 12, 1869, 29. ^■'Nouv. Corresp. Math., 1, 1874-5, 76.

'^Jour. fur Math., 81, 1876. 94. '^Bull. Soc. Math. France, 6, 1877-8, 52.

"Amer. Jour. Math., 1, 1878, 229, 230. For the second, anon.« of Ch. Ill (in 1830).

272 History of the Theory of Numbers. [Chap, ix

J. Wolstenholme"^ noted that the highest power of 2 dividing i^""^^)
isq — p — l, where q is the sum of the digits of 2m — I to base 2, and 2" is the
highest power of 2 dividing ?«.

J. Petersen"^ proved by Legendre's formula that C^'') equals the
product of the powers of all primes p, the exponent of p being (ta+tb — ta+b)
-^(p — 1), where ta is the sum of the digits of a to base p.

E. Cesaro^° treated Kummer's^^ problem. He stated (Ex. 295) and
Van den Broeek^^ proved that the exponent of the highest power of the
prime p dividing (-„") is the number of odd integers among [2n/p], [2n/p^],
[2n/p'],....

O. Schlomilch^^" stated in effect that („ + i) is divisible by n.

E. Catalan^'- proved that if n is odd,

p:)+io(t-^)

= 0 (modn+2).

W. J. C. Sharp^^" noted that {p-\-n)\ — p\n\ is divisible by p^, if p is a
prime >n. This follows also from (''t") — 1 (mod p) [Dickson^"].

L. Gegenbauer^^ noted that, if a is any integer, r one of the form 6s or
3s according as n is odd or even,

The case n odd, a = 2, r = 3, gives Catalan's result.

E. Catalan^ proved Hermite's'^^ theorem.

Ch. Hermite^^ stated that (Z) is divisible by m— n-f-1 if w is divisible
by n; by (m— n+l)/€ if e is the g. c. d. of m+1 and n; by m/8, if 5 is
the g. c. d. of m, n.

E. Lucas^^ noted that, ifn^p — 1, p — 2, p — 3, respectively,

(^;3)-(-ir(^^±lM)(:nodp),

if p is a prime, and proved Hermite's'^ result (p. 506).

F. RogeP^ proved Hermite's"^ theorem by use of Fermat's.

^*Jour. de math. 6\6m. et spec., 1877-81, ex. 360.

^»Tidsskrift for Math., (4), 6, 1882, 138-143.

soMathesis, 4, 1884, 109-110.

8'7feid., 6, 1886, 179.

«>"Zeitschrift Math. Naturw. Unterricht, 17, 1886, 281.

<«M6m. Soc. Roy. Sc. de Li6ge, (2), 13, 1886, 237-241 ( = Melanges Math.). Mathesis, 10, 1890.

257-8.
82aMath. Quest. Educ. Times, 49, 1888, 74.
s^Sitzunpsber. Ak. Wiss. Wien (Math.), 98, 1889, Ila, 672.
wM6m. Soc. Sc. Li^KC, (2), 15, 1888, 253-4 (Melanges Math. III).
«*Jour. de math, sp^ciales, problems 257-8. Proofs by Catalan, ibid., 1889, 19-22; 1891, 70;

by G. B. Mathews, Math. Quest. Educ. Times, 52, 1890, 63; by H. J. Woodall, 57,

1892, 91.
"Th^orie des nombres, 1891, 420. "Archiv Math. Phys., (2), 11, 1892, 81-3.

Chap. IX] DIVISIBILITY OF FACTORIALS, MULTINOMIAL COEFFICIENTS. 273

C. Szily^^ noted that no prime >2a divides

?M) •

and specified the intervals in which its prime factors occur.

F. Morley^^ proved that, if p = 2n+l is a prime, (2„")-(-l)"2*" is
divisible by p^ ii p>S. That it is divisible by p^ was stated as an exercise
in Mathews' Theory of Numbers, 1892, p. 318, Ex. 16.

L. E. Dickson^° extended Rummer's''^ results to a multinomial coefficient
M and noted the useful corollary that it is not divisible by a given prime p
if and only if the partition of m into nii,..., nit arises by the separate
partition of each digit of m written to the base p into the corresponding
digits oi TUi, . . . , rrit. In this case he proved that

^= n .1),''" .,, (mod p), m, = ao''Y-{- . . . +a,^''K

This also follows from (2) and from

(xi+ . . . +xtr= {x,+ ... +x,)"»(xiP+ . . . +x,o"»-i . . . (0^1^''+ . . . +x/'ro

(mod p).

F. Mertens^^ considered a prime p^n, the highest powers p" and 2" of
p and 2 which are ^n, and set n„ = [n/2"]. Then nl-^ {niln2l. . .nj} is
divisible by Up'", where p ranges over all the primes p.

J. W. L. Glaisher^^ gave Dickson's^" result for the case of binomial
coefficients. He considered (349-60) their residues modulo p"', and proved
(pp. 361-6) that if {n)r denotes the number of combinations of n things r
at a time, 'Z{n)r^(j)k (mod p), where p is any prime, n any integer =j
(mod p — l), while the summation extends over all positive integers r,
f"^n, r=k (mod p — l), and j, k are any of the integers 1,. . ., p — l. He
evaluated S[(?^)r-^p] when r is any number divisible by p — l, and (n)^ is
divisible by p, distinguishing three cases to obtain simple results.

Dickson^^ generalized Glaisher's^^ theorem to multinomial coefficients:
Let k be that one of the numbers 1, 2, . . ., p — l to which m is congruent
modulo p — l, and let ki,..., kt be fixed numbers of that set such that
ki-\- ■ ■ ■ -\-kt=k (mod p — l). Then if p is a prime,

where , . , m
(mi, . . . , nit) = J ;

The second of the two proofs given is much the simpler.

ssNouv. Ann. Math., (3), 12, 1893, Exercices, p. 52.* Proof, (4), 16, 1916, 39-42.

s^Annals of Math., 9, 1895, 168-170.

^"Ibid., (1), 11, 1896-7. 75-6: Quart. Jour. Math., 33, 1902, 378-384.

siSitzungsber. Ak. Wiss. Wien (Math.), 106, lla, 1897, 255-6.

'2Quar. Jour. Math., 30, 1899, 150-6, 349-366.

o^Ibid., 33, 1902, 381-4.

274 History of the Theory of Numbers. [Chap, ix

Glaisher^^ discussed the residues modulo p^ of binomial coefficients.
T. Hayashi^^ proved that if p is a prime and fjL+v = p,

(nsr>(-i)'C).».i(-<ip)-

according as 0<s^v, v<s<p, or s = 0.

T. Hayashi^^ proved that, if Iq is the least positive residue of I modulo p,
and if v = p—ii,

modulo p. Special cases of the first result had been given by Lucas. *^

A. Cunningham^^ proved that, if p is a prime,

(^;^)^(-ir (modp), ^(p^)^! (modp^p>3).

B. Ram^^ noted that, if (^), m = l,. . ., n — 1, have a common factor
o>l, then a is a prime and n = a''. There is at most one prime <n which
does not di\dde n(^) for m = l,. . ., n — 2, and then only when n+l=?a^
where a is a prime and q<a. For m = 0, 1, . . ., n, the number of odd (^)
is always a power of 2.

P. Bachmann^^ proved that, if h{p — l) is the greatest multiple <A; of

p-i,

(,!i)+(2(pii))+-+(M/-i>''("^°'^^>'

the case k odd being due to Hermite.'^

G. Fonten^ stated and L. Grosschniid^°° proved that

(p(pil))^(-l)' (^odp), P = p\ a^O.

A. Fleck^^i proved that, if 0^p<p, aH-6=0 (mod p),

N. Nielsen^"^ proved Bachmann's^^ result by use of Bernoulli numbers.

wQuar. Jour. Math., 31, 1900, 110-124.

"Jour, of the Physics School in Tokio, 10, 1901, 391-2; Abh. Geschichte Math. Wias., 28, 1910,
26-28.

"Archiv Math. Phys., (3), 5, 1903, 67-9.

•'Math. Quest. Educat. Times, (2), 12, 1907, 94-5.

"Jour, of the Indian Math. Club, Madras, 1, 1909, 39-43.

"Niedere Zahlentheorie, II, 1910, 46.
""•Xouv. Ann. Math., (4), 13, 1913, 521-4.
"'Sitzungs. BerUn Math. Gesell., 13, 1913-4, 2-6. Cf. H. Kapferer, Archiv Math. Phys.

(3), 23, 1915, 122.
"«Annali di mat., (3), 22, 1914, 253.

Chap. IX] DIVISIBILITY OF FACTORIALS, MULTINOMIAL COEFFICIENTS. 275

A. Fleck"^ proved that

if and only if p is a prime. The case a = 1 is Wilson's theorem.

Gu^rin^'^ asked if Wolstenholme's^^ result is new and added that

(iLij — ^~1 (modp^), p prime >3.

The Congruence 1-2-3. . .(p— 1)/2= ±1 (mod p).
J. L. Lagrange^^" noted that p — 1, p— 2, ..., (p+l)/2 are congruent
modulo p to —1, —2,..., — (p — 1)/2, respectively, so that Wilson's
theorem gives

(4) (l-2.3. . .P=iy^(-1)¥ (mod p).
For p a prime of the form 4n+3, he noted that

(5) l-2-3...^==tl (modp).

E. Waring^^^ and an anonymous writer^^^ derived (4) in the same manner.

G. L. Dirichlet^^^ noted that, since —1 is a non-residue of p = 4n+3, the
sign in (5) is -f or — , according as the left member is a quadratic residue or
non-residue of p. Hence if m is the number of quadratic non-residues
<p/2ofp,

l-2.3...^=(-ir (modp).

C. G. J. Jacobi^^^ observed that, for p>3, m is of the same parity as N,
where 2N—l = {Q—P)/p, P being the sum of the least positive quadratic
residues of p, and Q that of the non-residues. Writing the quadratic
residues in the form ^k, l^A;^|(p — 1), let m be the number of negative
terms —k, and — T their sum. Since — 1 is a non-residue, m is the number
of non-residues < ^p and

^{=i=k)=Sp, P=2{+k)-{-X{p-k)=mp+Sp,

Since p = 4n+3, N = n-\-l—m—S. But 7i-|-l and S are of the same parity
since

p>S+2r = l+2+...+Kp-l)=iy-l) = (2n-H)(n+l).

lo^Sitzungs. BerUn Math. GeseU., 15, 1915, 7-8.

lo^L'intermgdiaire des math., 23, 1916, 174.

""Nouv. M6m. Ac. BerHn, 2, 1773, ann6e 1771, 125; Oeuvres, 3, 432.

"iMeditat. Algebr., 1770, 218; ed. 3, 1782, 380.

i"Jour. fur Math., 6, 1830, 105.

"'/bid., 3, 1828, 407-8; Werke, 1, 107. Cf. Lucas, Th^orie des nombres, 438; rinterm^diaire

des math., 7, 1900, 347.
i"/6id., 9, 1832, 189-92; Werke, 6, 240-4.

276 History of the Theory of Numbers. [Chap, ix

He stated empirically that N is the number of reduced forms ay^+hyz-\-cz^,
4:ac — b~ = p for b odd, ac — \b~ = p for b even, where b<a, b<c.

C. F. Arndt^^^ proved in two ways that the product of all integers
relatively prime to M = %r or 2/)", and not exceeding (ilf — 1)/2, is =±1
(mod M), when p is a prime 4fe+3, the sign being + or — according as the
number of residues >M/2 of M is even or odd. Again,
{l-3-5-7...(p-2)}2=±l (modp),

the sign being + or — according as the prime p is of the form 4n+3 or
472+1. In the first case, 1-3. . .(p — 2)=±1 (mod p).

L. Kronecker^^^ obtained, for Dirichlet's^^^ exponent m, the result m=j/
(mod 2), where v is the number of positive integers of the form q^^^'^r^ in
the set p — 2^, p — 4", p — 6", . . ., and g is a prime not dividing r. Liou-
\'ille (p. 267) gave m=k-\-v" (mod 2), when p = 8^+3 and v" is the number
of positive integers of the form g'^'+V^ in the set p— 4^, p — 8^, p — 12^, . . ..

J. Liou\'ille^" gave the result ?n=cr+r (mod 2), for the case p = 8^'+3,
where r is the number of positive integers of the form 2g^'"^^ r^ {q a prime not
dividing r) in the set p — 1^, p— 3^, p — 5^, . . . , and a is the number of equal
or distinct primes 4gr+l di\'iding b, where p = a^+26" (uniquely).

A. Korkine^^^ stated that, if [x] is the greatest integer ^x,

_p-3

(p-3)/4

S [Vp^l (modp).

4
J. Franel"^ proved the last result by use of Legendre's symbol and

(-i)""'TG> ©=(-^)'' "-TBI (-°'^2)-

M. Lerch^^° obtained Jacobi's"* result.

H. S. Vandiver^^"" proved Dirichlet's"^ result and that

(p-i)/2r.-2-i
m= S Y~\ (mod 2).

R. D. CarmichaeP^^ noted that (4) holds if and only if p is a prime.

E. Malo^^^ considered the residue ±r of 1-2. . .(p — 1)/2 modulo p,
where p is a prime 4m+l, and 0<r<p/2. Thus r^= —1. The numbers
2, 3, . . ., (p — 1)/2, with r excluded, may be paired so that the product
of the two of a pair is = =•= 1 (mod p) . If this sign is minus for k pairs,
1-2. . .(p-l)/2=(-l)V (mod p).

*J. Ouspensky gave a rule to find the sign in (5).

Other Congruences Involving Factorials.

V. Bouniakowskyi29 noted that (p-l)! = PP', P±P'=0 (mod p) accord-
ing as p = 4/j=f1. For, if p is a primitive root of p, we may set P = pp^

I'SArchiv Math. Phys., 2, 1842, 32, 34-35. i^o^Amer. Math. Monthly, 11, 1904, 51-6.

"«Jour. de Math., (2), 5, 1860, 127. ^^'IMd., 12, 1905, 106-8.

^^Ubid., 128. '22i;interm6diaire des math., 13, 1906, 131-2

»«L'interm6diaire des math., 1, 1894, 95. »23Bu11. Soc. Phys. Math. Kasan, (2), 21.

"»/6id., 2, 1895, 35-37. i"M6m. Ac. Sc. St. P6tersbourg, (6), 1, 1831, 564.

'"Prag Sitzungsber. (Math.). 1898, No. 2.

Chap. IX] DiVISIBILTY OF FACTORIALS, MULTINOMIAL COEFFICIENTS. 277

...p\ P' = p'+^..p^-' with t = {v-l)/2, when p = 4A;-l; but P=pp''-^
pV-^ . ., P' = pY-'' pV"". • ., when p = 4A; + l.

G. 01tramare^^° gave several algebraic series for the reciprocal of the
binomial coefficient C^) and concluded that, if the moduli are primes,

!+(-')= -2{(i)%(||)%(i|^J+ . . .} (mod 4^+1),

2=+(-') = -K(iy+(riT+(wy+ ■ • •} ^^'^ *-+3)-

V. Bouniakowsky^^^ considered the integers qi,. . ., Qs, each <N and
prime to N, arranged in ascending order of magnitude. If X is any chosen
integer ^s, multiply

q, = N-qi, qs-i = N-q2,..., g,_x+i = iV-gx

together and multiply the resulting equation by qi. . . q^^x- Apply the
generalized Wilson theorem qi. . .g^+( — 1)^=0 (mod A'"). Hence

9i?2- • •5x-gi?2. . .g.-x-f(-l)'+^=0 (mod N).
For N a prime, we have s = N—l and

X!(iV-l-X)!+(-l)'=0 (mod N) (l^XSN-l).

C. A. Laisant and E. Beaujeux^^^ gave the last result and

{'-.'}

(-If (mod p), ^ = ^-

F. G. Teixeira^^^ proved that if a=-2^''-^p-a, a<2p-l,

a{a+l) . . .{a+2p-l)=3^-5\ . .{2p-iyp

(mod a+a+l+a+2+...+a+2p-l).
Thus, for p = 3, a = 1 , a = 95,

95-96-97-98-99-100=32-52-3 (mod 585 = 95+ •• .+100).

M. Vecchi^^^ noted that the final formula by Bouniakowsky^^^ follows
by induction. Taking X = (iV— 1)/2, we get Lagrange's formula (4).
From the latter, we get

{3.5-7. . . (22/-l)}2| (^^^^) \f/2'^^{-l)'^ (mod p).

The case y={p — l)/2 gives Arndt's"^ result

(6) {3-5-7...(p-2)P=(-l)~ (modp).

Vecchi^^^ proved that, if v is the number of odd quadratic non-residues
of a prime p = 4n+3, then 1-3-5. . .(p — 2) = ( — 1)" (mod p). If n is the
number of non-residues <p/2, 1-3-5. . .{p-2)={-iy+^2^''-^^^^ (mod p).

""M^m. de I'lnstitut Nat. Genevois, 4, 1856, "sjomal de Sciencias Math, e Astr., 3, 1881,

33-6. 105-115.

"iBull. Ac. Sc. St. P^tersbourg, 15, 1857, 202-5. i^^Periodico di Mat., 16, 1901, 22-4.

"2Nouv. Corresp. Math., 5, 1879, 156 (177). '^Hbid., 22, 1907, 285-8.

278 History of the Theory of Numbers. [Chap. DC

R. D. Carmichael^^^ proved that, if a+1 and 2a + 1 are both primes,
(a!)* — 1 is di^'isible by (a + l)(2a + l), and conversely.

A. Ar^valo^^^ proved (6) and Lucas'" residues of binomial coefficients.
N. G. W. H. Beeger"^ proved that [if p is a prime]

(p_l)!+l = s-p+l (rnodp^), s = l+2^-'-\- . . .+{p-iy-' = pK.„

where h is a. Bernoulli number defined by the symbolical equation (/i + l)"
= /i", hi = l/2. By use of Adams'^"" table of /i„ 2<114, it was verified
that p = 5, p = 13 are the only p<114 for which (p — 1)!+1=0 (mod p^).
T. E. Mason^^^ and J. M. Child^'^ noted that, if p is a prime >3,

inp)\ = nl(piy (modp"+^).

N. Nielsen^^'' proved that, if p = 2n+l, P=l-3-5. . . (2n-l),

(-l)'^2np2=22'».3.5. . . (4n-l) (mod IGn^).

If p is a prime >3, P=(-l)"2^"n! (mod p^). He gave the last result
also elsewhere. ^"^^

C. I. Marks"- found the smallest integer x such that 2-4. . .{2n)x is di-
visible by 3-5 ... (2n- 1).

i»«Revista de la Sociedad Mat. Espanola, 2, "»Math. Quest. Educat. Times, 26, 1914, 19.

1913, 130-1. ""Annali di mat., (3), 22, 1914, 81-2.

"'Messenger Math., 43, 1913-4, 83-4. »«K. Danske Vidensk. Selsk. Skrifter, (7), 10
""a Jour, fiir Math., 85, 1878, 269-72. 1913, 353.

"STohoku Math. Jour., 5, 1914, 137. "'Math. Quest. Educ. Times, 21, 1912, 84-6.

I

CHAPTER X.

SUM AND NUMBER OF DIVISORS.

The sum of the A;th powers of the divisors of n will be designated crk(n)
Often (r(n) will be used for (7i(n),and T{n) for the number ao{n)oi the divisors
of n; also,

!r(7i)=T(l)+T(2)+...+r(n).

The early papers in which occur the formulas for T{n) and a{n) were cited
in Chapter II.

L. Euler^'^'^ applied to the theory of partitions the formula

(1) p{x)='n.{l-x'')=s^l-x-x'+z^+x^-x'^-....

fc=l

Euler'' verified for n<300 that

(2) a{n)=(T{n-l)+(7{n-2)-a{n-b)-(j{n-7)+(7in-12)+.. .,

in which two successive plus signs alternate with two successive minus
signs, while the differences of 1, 2, 5, 7, 12, . . . are 1, 3, 2, 5, 3, 7, . . ., the
alternate ones being 1, 2, 3, 4, . . . and the others being the successive odd
numbers. He stated that (2) can be derived from (1).

Euler^ noted that the numbers subtracted from n in (2) are pentagonal
numbers (3a;^— a:)/2 for positive and negative integers x, and that if a(n—n)
occurs it is to be replaced by n. He was led to the law of the series s by
multipljdng together the earlier factors of p{x), but had no proof at that
time that p = s. Comparing the derivatives of the logarithms of p and s,
he found for —xdp/{pdx) the two expressions equated in

,„. « nx"" x+2x^-bx^-1x^+l2x^^+ . . .

{o) 2j ^=

n=l \—X S

He verified for a few terms that the expansion of the left member is
(4) I a;V(n).

n=l

Multiplying the latter by the series s and equating the product to the numer-
ator of the right member of (3), he obtained (2) from the coefficients of x".
Euler® proved (1) by induction. To prove (2), multiply the left member
of (3) by —dx/x and integrate. He obtained log p{x) and hence log s,
and then (3) by differentiation.

^Letter to D. Bernoulli, Jan. 28, 1741, Corresp. Math. Phys. (ed. Fuss), II, 1843, 467.

''Euler, Introductio in Analysin Infinitorum, 1748, I, ch. 16.

^Novi Comm. Ac. Petrop., 3, 1750-1, 125; Comm. Arith., 1, 91.

^Letter to Goldbach, Apr. 1, 1747, Corresp. Math. Phys. (ed. Fuss), I, 1843, 407.

»Posth. paper of 1747, Comm. Arith., 2, 639; Opera postuma, 1, 1862, 76-84. Novi Comm. Ac.
Petrop., 5, ad annos 1754-5, 59-74; Comm. Arith., 1, 146-154.

"Letter to Goldbach, June 9, 1750, Corresp. Math. Phys. (ed. Fuss), I, 1843, 521-4. Novi
Comm. Ac. Petrop., 5, 1754-5, 75-83; Acta Ac. Petrop., 41, 1780, 47, 56; Comm. Arith.,
1, 234-8; 2, 105. Cf. Bachmann, Die Analytische Zahlentheorie, 1894, 13-29.

279

280 History of the Theory of Numbers. [Chap, x

Material on (1) will be given in the chapter on partitions in Vol. II.
J. H. Lambert/ by expanding the terms by simple division, obtained

n = l 1—X

in which the coefficient of x"* is T{n). Similarly, he obtained (4) from the left
member of (3).

E. Waring^ reproduced Euler's^ proof of (2).

E. Waring^ employed the identity

n {x''-l)=x''-x'-'-x'-^+x'-^+x'-''- -...=A,

k=l

the coefficient of x^'", for v^n, being ( — 1)^ if v={3z^^z)/2 and zero if v is
not of that form. If m^n, the sum of the mth powers of the roots of
A=0 is a{m). Thus (2) follows from Newton's identities between the
coefficients and sums of powers of the roots. He deduced

m(m-l) ,o^ , m{m-l)im-2) m{m-l){m-2){m-S)
\o) I (t{2)-\ a{S) o-(4)

, ?n(m-l)(m-2)(m-3)( .^
+ ■■■+ ^ {o-(2)j^-...= c-ml,

where c= =•= 1 or 0 is the coefficient of x^~"* in series A. Let

U{x''-l)=x''-x'''-'-x''-^+x''-''-\-x''-^- . . . =A',

where p ranges over the primes 1, 2, 3, 5, . . ., n. If m^n, the sum of the
mth powers of the roots of A' = 0 equals the sum a'{m) of the prime divisors
of m. Thus

ff'(m) =(r'(w- 1) +o-'(m-2) -t7'(m-4) -o-'(w-8) +(r'(m- 10) +o-'(m- 11)
-(T'{m-12)-a'{m-lQ)+. . ..

We obtain (5) with a replaced by a', and c by the coefficient of ic^'"*" in series
A'. Consider

n {x^^-l)=x^-x^-^ -x^-2'+x^-^'+ ... =5,

with coefficients as in series A. The sum of the (Zm)th powers of the roots
of B = 0 equals the sum (T^^\m) of those divisors of m which are multiples of I.
Thus ^

(T'^'\m)=(T'^'^{m-l)W\m-2l)-a^'\m-U)- . . .,
with the same laws as (2) . The sum of those divisors of m which are divisible

'Anlage ziir Architectonic, oder Theorie des Ersten und des Einfachen in der phil. und math.

Erkenntniss, Riga, 1771, 507. Quoted by Glaisher.'*
^Meditationes Algebraicse, ed. 3, 1782, 345.
•Phil. Trans. Roy. Soc. London, 78, 1788, 388-394.

Chap. X] SuM AND NuMBER OF DiVISORS. 281

by the relatively prime numbers a,h, c,. . . is

Waring noted that o-(a|8) = ao-(/3) + (sum of those divisors of jS which are not
divisible by a) . Similarly,

<T(a^y . . . ) = aai^y . . . ) + (sum of divisors of 187 . . . not divisible by a)
= a(3a{yd . . .) + (sum of divisors of JS7. . . not divisible by a)
+a(sum of divisors of 76 . . . not divisible by jS),

etc. Again, (r^'^(a/3)=ao-^"(i8) + (sum of divisors of ^ divisible by I but not
by a). The generalization is similar to that just given for a.
C. G. J. Jacobi^^ proved for the series s in (1) that

00

s^ = l-3x-\-5x^-7x^+...= S (-l)"(2n+l) a;"'"+^)/2.

n=0

Jacobi^^ considered the excess E{n) of the number of divisors of the
form 4w + l of n over the number of divisors of the form 4m +3 of n. If
n = 2^uv, where each prime factor of u is of the form 4m + 1 and each prime
factor of V is of the form 4m+3, he stated that E{n) =0 unless y is a square,
and then E{n) =t{u).

Jacobi^^ proved the identity

(6) {l+x-{-x^-{- . . . +a;'(^+i)/24- . . .y = l-\-a(3)x+ . . . +(r(2n+lK+ ....

A. M. Legendre^^ proved (1).

G. L. Dirichlet^^ noted that the mean (mittlerer Werth) of (T{n) is x^n/6
— 1/2, that of T{n) is log n+2C, where C isEuler's constant 0.57721. . . .
He stated the approximations to T{n) and \pin), proved later^'^, without ob-
taining the order of magnitude of the error.

Dirichlet^^ expressed m in all ways as a product of a square by a com-
plementary factor e, denoted by v the number of distinct primes dividing e,
and proved that 22" = T(m).

Stern^^" proved (2) by expanding the logarithm of (1). If C"„ is the
number of all combinations with repetitions with the sum n,

(T(n)=nCn-C\ain-l)-C'2(T{n-2)- . . ..

Let S{n) be the sum of the even divisors of n. Then, by (1),

S{2n)=Si2n-2)-\-S{2n-4:)-S{2n-10)-Si2n-U)-\- . . ., S{0)=2n.

"Fundamenta Nova, 1829, § 66, (7); Werke, 1, 237. Jour, fiir Math., 21, 1840, 13; French
transl., Jour, de Math, 7, 1842, 85; Werke, 6, 281. Cf. Bachmann,« pp. 31-7.

"Zfeid., §40; Werke, 1, 1881, 163.

i^Attributed to Jacobi by Bouniakowsky" without reference. See Legendre (1828) and
Plana (1863) in the chapter on polygonal numbers, vol. 2.

"Th^orie des nombres, ed. 3, 1830, vol. 2, 128.

"Jour, fiir Math., 18, 1838, 273; Bericht Berlin Ak., 1838, 13-15; Werke, 1, 373, 351-6.

^'Ibid., 21, 1840, 4. Zahlentheorie, § 124.

i5»76id., 177-192.

282 History of the Theory of Numbers. [Chap, x

Let S'(n) be the sum of the odd di\'isors of n, and C„ be the number of all
combinations without repetitions with the sum n, so that C7 = 5. Then

S'in)=nCn-S'{n-l)Ci-S\n-2)C2+ . . .,

Z)(n) = -D(n-l)-D(n-3)-D(n-6)-..., D{n)=S'{n)-S{n).

A complicated recursion formula for T(n)is derived from

\og{{l-x){l-x^y{l-3^)r . .} = - I ^-Tin)x\

n=in

Complicated recursion fonnulas are found for the number of integers
<m not factors of m, and for the sum of these integers. A recursion
formula for the sum Sr{n) of the di\'isors ^r of n is obtained by expanding

log {l-x)(l-x2)...(l-a:'-)l = - S -Sr(n)x".

n=in

Jacobi^® proved (1).

Dirichlet^^ obtained approximations to T(n). An integer s^n occurs
in as many terms of this sum as there are multiples of s among 1, 2, . . . , n.
The number of these multiples is [n/s], the greatest integer ^n/s. Hence

''(")=iG]

This sum is approximately the product of n by

£i = logn+C+i+....

Hence T{n) is of the same order of magnitude as n log n.

Let ju be the least integer ^ y/n and set v = [n/ii]. Then if g{x) is any
function and G{x)=g{l)-\-g{2)-\- . . . +^(x),

2 r^i^(s)= -.GGu)+s pi^(s)+s Gjr^ii-

»=:LsJ «=iLsJ «=i LLsJJ

In particular, if ^(x) = 1,

«=iLsJ «=iLsJ
Giving to [n/s] the approximation n/s, we see that
(7) T(n)=n log,n+(2C-l)n+e,

where € is of the same order of magnitude as Vn.

Let pin) be the number of distinct prime factors >1 of ti. Then 2"^"^ is
the number of ways of factoring n into two relatively prime factors, taking

"Jour, fur Math., 32, 1846, 164; 37, 1848, 67, 73.

"Abhand. Ak. Wiss. Berlin, 1849, Math., 69-83; Werke, 2, 49-66. French transl., Jour, de
Math., (2), 1, 1856, 353-370.

4

Chap. X] SuM AND NuMBER OF DiVISORS. 283

account of the order of the factors. The number of pairs of relatively prime
integers ^, 17 for which ^r^^n is therefore

y=i
For the preceding C and r(n), it is proved that

r(n)=S^,/.[P], . t = [V^],
^in)=^(log.n+'-^+2C-l)+m, " C- I H^,

IT IT 8=2 S

where m is of the order of magnitude of n\ 8>y/2, while 7 is determined by
2)s~^ = l (s = 2 to 00). Moreover, T(n) is the number of pairs of integers
X, y for which xy^n. He noted that

(7(l)+(r(2) + ...+(r(n)=Ssr^l

8=1 Ls-i

and that the difference between this sum and ir^n^/12 is of an order of magni-
tude not exceeding n loge n.

G. H. Burhenne^^ proved by use of infinite series that

r(n)=i2)/"K0), fix)^- "^^

and then expressed the result as a trigonometric series.

V. Bouniakowsky^^ changed x into x^ in (6), multiplied the result by x'^
and obtained

(x^ +x' +x^ + . . .)* = x*+(r(3)x'2_^ . . . +(r(2w+l)a:^"'+H ....

Thus every number 8m+4 is a sum of four odd squares in (r(2w+l) ways.
By comparing coefficients in the logarithmic derivative, we get

(8) (l2-2m+l)(r(2m+l) + (3^-2m-l)(7(2m-l) + (52-2m-5)(r(2m-5)

+ ...=0,

in which the successive differences of the arguments of <r are 2, 4, 6, 8, ... .
For any integer N,

(9) {l^-N)a{N) + {S^-N-h2)(r{N-l-2) + i5''-N-2-3)a{N-2'3)

+ -..=0,

where o-(O) , if it occurs, means A^/6. It is proved (p. 269) by use of Jacobi's^°
result for s^ that

l+x+x'+x'+ . . . =P^= (i+x)a+x'){l+x') . . .
{l-x')(l-x'){l-x')...,

"Archiv Math. Phys., 19, 1852, 442-9.

»M6m. Ac. Sc. St. P^tersbourg (Sc. Math. Phys.), (6), 4, 1850, 259-295 (presented, 1848).
Extract in Bulletin, 7, 170 and 15, 1857, 267-9.

284 History of the Theory of Numbers. [Chap, x

where the exponents in the series are triangular numbers. Hence if we
count the number of ways in which n can be formed as a sum of different
terms from 1, 2, 3, . . . together w^ith different terms from 2, 4, 6, . . ., first
taking an even number of the latter and second an odd number, the differ-
ence of the counts is 1 or 0 according as n is a triangular number or not.
It is proved that

(10) <r(n) + {(T(2)-4o-(l))(r(n-2)+(r(3)(T(n-4) + {(r(4)-4(r(2))(r(n-6)
+(r(5)(7(n-8) + {(r(6)-4(r(3))tr(n-10)+. . . =^(7(n+2).

The fact that the second member must be an integer is generaUzed as
follows: for n odd, (T(n) is even or odd according as n is not or is a square;
for n even, (T{n) is even if n is not a square or the double of a square, odd in the
contrary case. Hence squares and their doubles are the only integers whose
sums of divisors are odd.

V. Bouniakowsky-'^ proved that (r(A^) = 2 (mod 4) only when N = kc^ or
2kc^, where A: is a prime 4Z+1 [corrected by Liouville^°].

V. A. Lebesgue-^ denoted by l-{-AiX+A2X^-\- . . . the expansion of the
mth power of p{x), given by (1), and proved, by the method used by Euler
for the case m = 1, that

a{n)+A,a{n-l)-\-A2<T{n-2)+ . . .+Ar,_,a{l)-\-nAjm = 0.
This recursion formula gives

. m(m— 3) . —m(m — l)(m — S)
A,= -m, A, = — ^^2— ' ^^ = 1:2:3 ••••

The expression for Aj, was not found.

E. MeisseP2 proved that (c/. Dirichlet^^)

(11) T{n) = i^[jj =^i:[j] -'' (^ = [V^])-

J. Liouville^^ noted that by taking the derivative of the logarithm of
each member of (6) we get the formula, equivalent to (8) :

J 5m(m+l)1 /o , 1 2 N n
S^n ^ Ya{2n+l—m—m)=0,

summed for m = 0, 1, . . ., the argument of a remaining ^0.
J. Liouville^^ stated that it is easily shown that

Sd<T(d)=s(|y(r(d),

20M6m. Ac. Sc. St. P^tersbourg, (6), 5, 1853, 303-322.
"Nouv. Ann. Math., 12, 1853, 232-4.
"Jour, fur Math., 48, 1854, 306.
"Jour, de Math., (2), 1, 1856, 349-350 (2, 1857, 412).

^Ibid., (2), 2, 1857, 56; Nouv. Ann. Math., 16, 1857, 181; proof by J. J. Hemming, ibid., (2), 4,
1865, 547.

Chap. X] SuM AND NuMBER OF DiVISORS. 285

where d ranges over the divisors of m. He proved (p. 411) that

S(-l)'"/'^fi = 2(T(m/2)-(7(m).

J. Liouville^^ stated without proof the following formulas, in which d
ranges over all the divisors of m, while 5 = m/d :

Xaid) =2:5r(d), S0(d)r(5) =(r(m), 20(d)r(6) = [rim)}^,

XcT{d)cr{8) =SdT(d)r(5), Sr(d)r(5) =2:|t(^)}'

where (}){d) is the number of integers < d and prime to d, 6{d) is the number of
decompositions of d into two relatively prime factors, and the accent on S
denotes that the summation extends only over the square divisors D^ of m.
He gave (p. 184)

S0(cf)=r(m2), ^'e{^)i=r{m),

the latter being implied in a result due to Dirichlet.^^

Liouville"*' gave the formulas, numbered (a),. . ., {k) by him, in which
X(m) = +1 or —1, according as the total number of equal or distinct prime
factors of m is even or odd:

Sr(d2'')=T(m)r(m''), 2r(d2'')T(5) =ST(d)rOT, S(^(5)(7((i) =mT(m),
S5(7(d) =SdT(d), SX(c^) = 1 or 0, ^\{d)d{d)r{b) = 1 or 0,

according as m is or is not a square;

i:\{d)d{d)r{h^) = l, X\{d)e{d)=\im), SX(d)0(5) = l,

l^X{d)d{d)did)=0, SX(5)o-(ci) =mS'-^.

The number of square divisors D^ of m is '2\(d)T{8).

Liouville^^ gave the formulas, numbered I-XVIII by him:

ST(52)(/)(d) =S5^(d), Sdr(52) =S^(5)(r(d),

ST(52)X(d) =T(m), 2 {T{8)}Md)d{d) =tW,

S0(d)T(5)r(5'') =SdT(62''), ^e{b)T{d)r{d'') =Sr(52)T(d-''),

ST(52'')(7(d) =25r(d)T(d''), S'0(i))T(^) =S'Z) ^(^) ,

SX(5)T(d)TW =2't(^) . ^\id)(T{d) =mX(m)S'-

2)2

'^Jour. de Mathematiques, (2), 2, 1857, 141-4. "Sur quelques fonctiona num^riques," 1st article.

Here Sa6c denotes S(a6c).
^^Ihid., 244-8, second article of his series.
"76id., 377-384, third article of his seriea

286 History of the Theory of Numbers. [Chap, x

S'X(i))r(^2) =^"d(^^' 2{W!'' = T(m^),

Sr(0^(5) =S{^(d))''T(52), 2r(OX(5) =2|0(^) j^

where, in 2", e ranges over the biquadrate divisors of m.
Liouville^^ gave the formula

X{T{d)V={Xr{d)]',

which implies that if 2m (m odd) has no factor of the form 4)u+3 and if we
find the number of decompositions of each of its even factors as a sum of
two odd squares, the sum of the cubes of the numbers of decompositions
found will equal thesquare of their sum. Thus, for m = 25,

50=l2+72 = 72+l2 = 52+5^ 10 = 32+12 = 12+32, 2 = 1 + 1,

whence 3H2Hl' = 62.

Liouville2^ stated that, if a, 6, . . . are relatively prime in pairs,

a^iah. . .)=o'n(oVn(?>)- • •,
while if p, 9, . . . are distinct primes,

He stated the formulas

2(r^((i)</)(5) =m<T,_,{m), 2ciV,(5) =2d''(T^(5),

2X(d)r(d2)(r^(5) =2d''r(5)X(5), 2dV^(6) =2c/''r(d),

2dX(d) =252v,(d), 2dV3,(5) =2c^V2,(d),

2dX+,(d)(7,(5) =2(iV,+,(d)(r,(5), 2X(d)(T,(5) =S'(^)'

2T(d2'')(r,(5) =2^^(5)7(5"), 2{^(rf)} V,(5) =2d''r(52'),

and various special cases of them. To the seventh of these Liouville^" later
gave several forms, one being the case p = 0 of

2d''-V.+X^)(r,+,(5)=2d''-X+,((i)(r,+,(5),

and proved (p. 84) the known theorem that a{m) is odd if and only if m is a
square or the double of a square [cf. Bouniakowsky,^^ end]. He proved that
(t{N) = 2 (mod 4) if and only if N is the product of a prime 4X + 1, raised to
the power 4Z + 1 (Z^O), by a square or by the double of a square not divis-

"Jour. de Math6matiques, (2), 2, 1857, 393-6; Comptes Rendus Paris, 44, 1857, 753,
^^Ibid., 425-432, fourth article of his series,
"/bid., (2), 3, 1858, 63.

Chap. X] SuM AND NuMBER OF DiVISORS. 287

ible by the prime 4X+1. The condition given by Bouniakowsky^° is neces-
sary, but not sufficient. Also,

o-3(m) = S <T{2j-l)a{2m-2j+l) {m odd).

J. Liouville's series of 18 articles, "Sur quelques formules . . .utiles dans la
th^orie des nombres," in Jour, de Math., 1858-1865, involve the function
(r„, but will be reported on in volume II of this History in connection with
sums of squares. A paper of 1860 by Kronecker will be considered in
connection with one by Hermite.'^'^

C. Traub^^ investigated the number {N; M, t) of divisors T oi N which
are = t (mod M) , where M is prime to t and N. Let a,h,. . .,lhe the integers
< M and prime to M ; let them belong modulo M to the respective exponents
a', h',. . ., V; let m be a common multiple of the latter. Since any prime
factor of N is of the form Mx+k, where k = a,. . .,1, any T is congruent to

a^6^. . .Z^=« (mod M), O^A<a',. . ., O^KV.

Let A',. . ., L' he one of the n sets of exponents satisfying these conditions.
If P is a primitive mth root of unity, the function

1/' = ^7-^SP^ e = {A-A')am/a'+ . . .+{L-L')\m/V,

summed for all sets 0^a<a', . . ., O^X<r, has the property that i^ = l if
A = A'(mod a'),. . ., L=L'(mod V) simultaneously, while i/' = 0 in all other
cases. Thus {N] M, t) =SSt/', where one summation refers to the n sets
mentioned, while the other refers to the various divisors T of N. This
double sum is simplified.

[The properties found (pp. 278-294) for the set of residues modulo M
of the products of powers oi a,. . ., I may be deduced more simply from the
modern theory of commutative groups.]

V. Bouniakowsky^^ considered the series

n=l'c. n=l "'

By forming the product of xl/ix)""'^ by \{/{x) , he proved that z„, 2 is the number
No{n)=T{n) of the divisors of n, and Zn,m equals

where (and below) d ranges over the divisors of n. Also,

\p(x)\l/{x-l)= 2) ——•

n=l '«'

From \l/{xYxl/(x-iy for (i, j) = (2, 1), (2, 2), (1, 2), he derived the first and
fourth formulas of Liouville's^^ first article and the fourth of his^^ second
article. He extended these three formulas to sums of powers of the divisors

^lArchiv Math. Phys., 37, 1861, 277-345.

32M^m. Ac. Sc. St. P^tersbourg, (7), 4, 1862, No. 2, 35 pp.

288 History of the Theory of Numbers. [Chap, x

and proved the second formula in Liouville's first article and the first two
summation formulas of Liouville.-^ He proved

i.(2.-l)=2.-l+z[^-^], .= [^],

where 77 = 1 or 0 according as 2o-— 1 is divisible by 3 or not. The last two
were later generaUzed by Gegenbauer.^^

E. Lionnet^ proved the first two formulas of Liouville.^^

J. Liou^ille^ noted that, if q is divisible by the prime a,

(r,(a5)+a''a-M^|j = (a'' + l)(r,(g).

C. Sardi^^ denoted by A„ the coefficient of x" in Jacobi's^'' series for s^,
so that An = 0 unless n is a triangular number. From that series he got

S(-l)P(2p+l)(7{7i-p(p + l)/2)=(-l)^'+^'/W3orO {t = Vl+8n),
p
according as n is or is not a triangular number, and

|.4„+A„_,cr(l)+...+Ai(r(n-l)+Ao(r(n)=0.

This recursion formula determines A„ in terms of the c's, or (T{n) in terms of
the A's. In each case the values are expressed by means of determinants of
order n.

IM. A. Andreievsk}^^ wrote N^h^^i for the number of the divisors of the
form 4/i± 1 of n = a'^h^ . . . , where a, b,. . . are distinct primes. We have

where d ranges over all the di\'isors of n and the symbols are Legendre's.
Evidently „ /-i\a'

S (— ^) = a + l if a = 4Z + l,

a'=o\ a }

= 0 or 1 if a = 4Z-l,

according as a is odd or even. Hence, if any prime factor 4Z — 1 of n occurs
to an odd power, we have iV4A+i=iV4A_i. Next, let *|

where each p, is a prime of the form 4Z + 1 , each g, of the form 4? — 1 . Then

iV4A+i-iV4.-i = (ai + l)(ao + l). . . =r(^), D = q,\^\ . ..

^'Souv. Ann. Math., (2), 7, 1868, 68-72.

"Jour, de math., (2), 14, 1869, 263-4.

"Giomale di Mat., 7, 1869, 112-5.

3%Iat. Sbomik (Math. Soc. Moscow), 6, 1872-3, 97-106 (Russian).

Chap. X] SUM AND NUMBER OF DiVISORS. 289

The sum of the N's is T{n) ^riD^Mn/D^). Hence

N^^^rm + l

which is never an integer other than 1 or 2 when n is odd. If it be 2, t(D^) = 3
requires that D be a prime. Similarly, for Legendre's symbol (2/a),

is zero if any prime factor 8^± 3 of n occurs to an odd power, but is 11 (a^H- 1)
if in n each p, is a prime 8Z±1 and each Qi a prime 8Z±3. For n odd,
Ngh^i/Nsh^s can not be an integer other than 1 or 2; if 2, D is a prime.

F. Mertens" proved (11). He considered the number v{n) of divisors
of n which are not divisible by a square > 1. Evidently v{n) =2", where p
is the number of distinct prime factors of n. If ju(n) is zero when n has a
square factor > 1 and is + 1 or — 1 according as n is a product of an even or
odd number of distinct primes, v{n) =XiJL^{d), where d ranges over the divisors
of n. Also,

fc=i k=i \/c /

He obtained Dirichlet's^'^ expression \l/{n) for this sum, finding for m a limit
depending on C and n, of the order of magnitude of \/n log^ n.

E. Catalan^'^" noted that So-(i)o-(i) =80-3(72) where i-{-j = 4n. Also, if i is
odd, €r{i) equals the sum of the products two at a time of the E's of the odd
numbers whose sum is 2i, where E denotes the excess of the number of
divisors 4/i+l over the number of divisors 4/^ — 1.

H. J. S. Smith^^ proved that, if m = pi''ip2"2. . .,

..W-2..(^)+S.,(^)-. ..=.•-

For, if P=l+p'+...+p", P' = l+p'+...+p'"-"', then

c.(m) = P.P. ... , <.. (^) = P/P, . . . , a. (^J = P/P/Pa ....

and the initial sum equals (Pi — Pi){P2 — P2) ■ . .=m\

J. W. L. Glaisher^^ stated that the excess of the sum of the reciprocals of
the odd divisors of a number over that for the even divisors is equal to the
sum of the reciprocals of the divisors whose complementary divisors are
odd. The excess of the sum of the divisors whose complementary divisors
are odd over that when they are even equals the sum of the odd divisors.

G. Halphen^° obtained the recursion formula

(T(n)=3(r(n-l)-5(r(n-3)+. . . -(-l)"(2a;+l)Jn-^^^^|+. . .,

"Jour, flir Math., 77, 1874, 291-4.

^'"Recherches sur quelques produits indefinis, M^m. Ac. Roy. Belgique, 40, 1873, 61-191.

Extract in Nouv. Ann. Math., (2), 13, 1874, 518-523.
asProc. London Math. Soc, 7, 1875-6, 211.
'^Messenger Math., 5, 1876, 52.
^oBuU. Soc. Math. France, 5, 1877, 158.

290

History of the Theory of Numbers.

[Chap.X

where, if n is of the form x{x+l)/2, (t(0) is to be taken to be n/3 [Glai-
sher^"]. The proof follows from the logarithmic derivative of Jacobi's^"
expression for s^, as in Euler's^ proof of (2).

Halphen"*^ formed for an odd function /(z) the sum of s.i

pc!

(-1)7

(t*«)'

n-

■ +^n-l — "~o-^n>

X taking all integral values between the two square roots of a, and y ranging
over all positive odd divisors of a—x^. This sum is

if a is a square, zero if a is not a square. Taking /(s) =z, we get a recursion
formula for the sum of those di\dsors d oi x for which x/d is odd [see the
topic Sums of Squares in Vol. II of this History]. Taking f{z)=a^ —oT',
we get a recursion formula for the number of odd di\dsors <a/m of a.
A generalization of (2) gives a recursion formula for the sima of the divisors
of the forms 2nk, n{2k-\-\)^m, wdth fixed n, m.

E. Catalan^'- denoted the square of (1) by l+LiX+ . . . +L„x'*H- . . ..
Thus

o-(n) +IiO-(7i- 1) +L20-(n-2) +

I'n-I>n-l-I>.-2+I^n-54-Z>„_7- . . . = 0 Or (2X + 1)(-1)\

according as n is not or is of the form X(X + l)/2. In \dew of the equality
of (3) and (4) and the fact that l/p=2;/'(n)x", where yp{n) is the number of
partitions of n into equal or distinct positive integers, he concluded that

(7(n)=;//(n-l)+2,/'(n-2)-5;/'(n-5)-7i/^(n-7) + 12^(n-12)+. . .".

J. W. L. Glaisher^^ noted that, if B{n) is the excess of the sum of the odd
di\'isors of n over the sum of the even dii'isors,

e{n) +<9(n - 1) +d{n - 3) +d{n - 6) -f . . . = 0,

where 1, 3, 6, . . . are the triangular numbers, and B{n—n) = —n.

E. Cesaro^ denoted bj^ s„ the sum of the residues obtained by dividing n
by each integer <n, and stated that

s„+(7(l)+(7(2)+...+(7(n)=n2.

E. Catalan^^ proved the equivalent result that the sum of the divisors of
1, . . . , n equals the sum of the greatest multiples, not >/?, of these numbers.
Catalan'*^ stated that, if <^(a, n) is the greatest multiple ^^ of a,

n

a{n)= 2 {</)(a, n)—4>{a, n — 1)).

I

"Bull. Soc. Math. France, 6, 1877-S, 119-120, 173-188.

"Assoc, frang. avanc. sc, 6, 1877, 127-8. Cf. Catalan.^^"

«Messenger Math., 7, 1877-8, 66-7.

"Nouv. Corresp. Math., 4, 1878, 329; 5, 1879, 22; Nouv. Ann. Math., (3), 2, 1883, 289; 4, 1885,

473.
«/Wd., 5, 1879, 296-8; stated, 4, 1879, ex. 447.
*mid., 6, 1880, 192.

Chap. X] SuM AND NuMBER OF DiVISORS. 291

Radicke (p. 280) gave an easy proof and noted that if we take n = 1, . . . , m
and add, we get the result by E. Lucas^^

o-(l) + . . . +o-(m) =0(1, m) + . . . +0(m, m).

J. W. L. Glaisher^^ stated that if f{n) is the sum of the odd divisors of n
and if g{n) is the sum of the even divisors of n, and /(O) =0, g{0) =n, then
/(n)+/(n-l)+/(n-3)+/(n-6)+/(n-10) + ...

= g{n)+g{n-l)+gin-S)+ . . ..
Chr.Zeller^^ proved (11).

R. Lipschitz^o wrote G(t) for <t{1)-\- . . .-\-a{t), D{t) for {t''+t)/2, and
$(0 for (^(1) + . . . +(f>{t), using Euler's (f>{t). Then if 2, 3, 5, 6, . . . are the
integers not divisible by a square > 1 ,

^w--[l]--[l]--G]

+ . . . =n,

G(n)-2G
D(n)-D

the sign depending on the number of prime factors of the denominator. He
discussed (pp. 985-7) Dirichlet's^'^ results on the mean of T{n), o-(n), (f>{n).

A. Berger^^ proved by use of gamma functions that the mean of the sum
of the divisors d of n is ir^n/Q, that of S d/2'^ is 1, that of Sl/d! is ir^/Q,

G. Cantor^^" gave the second formula of Liouville^^ and his^^ third.

A. Piltz^^ considered the, number Tk{n) of sets of positive integral solu-
tions of Ui. . .Uk = n, where differently arranged u's give different sets.
Thus T'i(n) = 1, T'2(n) =T{n). If a- is the real part of the complex number s,
and n* denotes e^ '°^ " for the real value of the logarithm, he proved that

n=l "' m = 0

where l = \—(T — \/k, and the 6's are constants, 6^ = 0 for s ?^ 1 ; while 0(/) is^'^
of the order of magnitude of /. Taking s = 0, we obtain the number 'SiTkin)
of sets of positive integral solutions of t^i . . .u^'^x.

H. Ahlborn^Hreated (11).

E. Cesaro^^ noted that the mean of the difference between the number
of odd and number of even divisors of any integer is log 2 ; the limit for

^^Nouv. Corresp. Math., 5, 1879, 296.

48NOUV. Corresp. Math., 5, 1879, 176.

"Gottingen Nachrichten, 1879, 265.

^oComptes Rendus Paris, 89, 1879, 948-50. Cf. Bachmann^" of Ch. XIX.

"Nova Acta Soc. Sc. Upsal., (3), 11, 1883, No. 1 (1880). Extract by Catalan in Nouv. Corresp.

Math., 6, 1880, 551-2. Cf. Gram.«^«
"«G6ttmgen Nachr., 1880, 161; Math. Ann., 16, 1880, 586.
"Ueber das Gesetz, nach welchem die mittlere Darstellbarkeit der natiirlichen Zahlen ala

Produkte einer gegebenen Anzahl Faktoren mit der Grosse der Zahlen wachst. Diss.,

Berlin, 1881.
"Progr., Hamburg, 1881.
"Mathesis, 1, 1881, 99-102. Nouv. Ann. Math., (3), 1, 1882, 240; 2, 1883, 239, 240. Also

Ces^ro," 113-123, 133.

292 History of the Theory of Numbers. [Chap, x

7i= 00 of r(r2)/(n log r?) is l;cf. (7); themean of 2(d+p)-' is (1 + 1/2+...
+ l/p)/P- -'^s generalizations of Berger's^^ results, the mean of H.d/'p^ is
l/(p — 1); the mean of the sum of the rth powers of the divisors of n is
^r ^(/--f 1) and that of the inverses of their rth powers is f(r+l), where

(12) f(s)=ilM

n=l

J. W. L. Glaisher^^ proved the last formula of Catalan^^ and

(r(n)-(r(n-4)-(r(n-8)+(T(n-20)+o-(n-28)-...

= Q(n-l)+3Q(n-3)-6Q(n-6)-10Q(n-10)+...,

where Q{n) is the number of partitions of n without repetitions, and 4, 8,
20, . . . are the quadruples of the pentagonal numbers. He gave another
formula of the latter tj-pe.

R. Lipschitz,^^ using his notations,^" proved that

7'(n)-.r0+.r[^]-...=n+z[|],
G(n)-SaGg]+2«6G[^] - . . . =n+Sp[|],

D(.) -SD [2] +XD [^] - . . . =$(n) +2*[|] ,

where P ranges over those numbers ^ n which are composed exclusivelj'' of
primes other than given primes a,h,. . ., each ^ n.

Ch. Hermite"^ proved (11) very simply.

R. Lipschitz^^ considered the number T^it) of those divisors of t which are
exact sth powers of integers and proved that

where p' is the largest sth power ^rz, and v = [n/ii']. The last expression,
found by taking /i = [n^^"^*^" ], gives a generahzation of (11).

T. J. Stieltjes^^ proved (7) by use of definite integrals.

E. Cesaro^° proved (7) arithmetically and (11).

E. Cesaro^^ proved that, if d ranges over the divisors of n, and 5 over
those of X,

(13) 2G(d)/Q)=2^(d)FQ), F{x)^i:fi8), G{x)^Xg{8).
Taking g(x) = l,f{x) =x, 4>{x), 1/x, we get the first two formulas of Liouville^^

"Messenger Math., 12, 1882-3, 16&-170.

"Comptes Rendus Paris, 96, 1883, 327-9.

"Acta Math., 2, 1883, 299-300.

"/&id., 301-4.

5»Cdmpte9 Rendus Paris, 96, 1883, 764-6.

^Hhid., 1029.

"Mdm. Soc. Sc. Li^e, (2), 10, 1883, Mem. 6, pp. 26-34.

Chap. X] SuM AND NuMBER OF DiVISORS. 293

and the fourth of Liouville.^^ Taking g = x, f=(t>, we get the third for-
mula of Liouville.^^ For g=l/x,f=(j), we get

S#(d)(7 0)

^ =Sdl

For g=(f) or x'',f=x% we get the first two of Liouville's^^ summation formulas.
If ir(x) is the product of the negatives of the prime factors 5^ 1 of a:,

Sx(d)*(d)<70)i = T(»), ST(d)<#,(d)J3 = ^,2#(d).

Further specializations of (13) and of the generalization (p. 47)

2G(d)/(^) =i:F(d)g(^fj, F{x)^l:^|^{^)f(^^y G(a;) ^2,^(5)^ (^),

led Cesaro (pp. 36-59) to various formulas of Liouville^^"^^ and many-
similar ones. It is shown (p. 64) that

n=l fl' n=l "•

for f and F as in (12), (13). For /(n) =(^(n), we have the result quoted
under Cesaro^^ in Ch. V. For/(n) = 1 and n'', m — k>l,

^—^=r{m), S-— - = ^(m)f(m-A;).

n=l '«' n '«'

If (n, j) is the g. c. d. of n, j, then (pp. 77-86)

.ST^-jr = 2S(7(d)-l, nT(n)=i:a{n,j), <j{n)=^T{n, 3),

S (Tk{n, j)=n(Tk-i(n), ^j(T{n, j) =-^lnT{n)-\-a{n)}.

y=i ^

If in the second formula of Liouville^^ we take m = l,. . .,n and add, we get

s0(i)rr?i=s<T(i).

Similarly (pp. 97-112) we may derive a relation in [x] from any given relation
involving all the divisors of x, or any set of numbers defined by x, such as
the numbers a, h,. . . for which x — a^, x — W,. . . are all squares. Formula
(7) is proved (pp. 124-8). It is shown (pp. 135-143) that the mean of the
sum of the inverses of divisors of n which are multiples of k is 7rV(6A;^) ; the
excess of the number of divisors 4)U+1 over the number of divisors 4^i+3
is in mean 7r/4, and that for 4/x+2 and 4ju is ^ log 2; the mean of the sum of
the inverses of the odd divisors of any integer is ttYS ; the mean is found of
various functions of the divisors. The mean (p. 172) of the number of
divisors of an integer which are mth powers is f(^)j and hence is 7rV6 if

294 History of the Theory of Numbers. [Chap, x

m = 2. The mean (pp. 216-9) of the number of divisors of the form aix+r
of n is, for r>0,

i+ijlog«/a+2C-/;ij^dx}

(cf. pp. 341-2 and, for a = 4, 6, pp. 136-8), while several proofs (also, p. 134)
are given of the known result that the number of divisors of n which are
multiples of a is in mean

-(log7i/a+2C).
a

If (pp. 291-2) a ranges over the integers for which [2n/d] is odd, the
number (sum) of the a's is the excess of the number (sum) of the divisors of
n + 1, n+2, . . . , 2n over that of 1, . . . , n; the means are n log 4 and 7rW/6.
If (pp. 294-9) k ranges over the integers for which [n/k] is odd, the number
of the A:'s is the excess of the number of odd divisors of 1, . . ., n over the
number of their even divisors, and the sum of the A;'s is the sum of the odd
divisors of 1, . . . , w; also

S*W=9^ 9=[^]'

Several asymptotic evaluations by Cesaro are erroneous. For instance,
for the functions \{n) and At(n), defined by Liouville^^ and Mertens,^^
Cesaro (p. 307, p. 157) gave as the mean values 6/7r^ and 36/7r*, whereas
each is zero.^^

J. W. L. Glaisher^^ considered the sum A(n) of the odd divisors of n.
If n = 2^m {m odd), A(n) =(j{m). The following theorems were proved by
use of series for elliptic functions :

A(l)A(2n-l)+A(3)A(2n-3)+A(5)A(2n-5)+...+A(2n-l)A(l)

equals the sum of the cubes of those divisors of n whose complementary
divisors are odd. The sum of the cubes of all divisors of 2n+l is

A(2n+l) + 12{A(l)A(2n)+A(2)A(2n-l)+. . . +A(2n)A(l)).

If A, £, C are the sums of the cubes of those divisors of 2n which are respec-
tively even, odd, with odd complementary divisor,

2A(2n)+24JA(2)A(2n-2)+A(4)A(2n-4)+. . .+A(2n-2)A(2))

= i(2A-2J5-C)=i(3-23^-10)5
o 7

if 2n = 2'"m (ttz odd). Halphen's formula^*' is stated on p. 220. Next,

n(r(2n+l) + (n-5)(r(2n-l) + (n-15)(T(2n-5)

+ (n-30)(7(2n-ll)+. . . =0,

"H. V. Mangoldt, Sitzungsber. Ak. Wiss. Berlin, 1897, 849, 852; E. Landau, Sitzungsber, Ak.

Wiss. Wien, 112, II a, 1903, 537.
«Quar. Jour. Math., 19, 1883, 216-223.

Chap. X] SuM AND NuMBER OF DiVISORS. 295

in which the differences between the arguments of a in the successive terms
are 2, 4, 6, 8, ... , and those between the coefficients are 5, 10, 15, ... , while
o-(O) =0. Finally, there is a similar recursion formula for A(n).

Glaisher^^ proved his^^ recursion formula for Q{n), gave a more compli-
cated one and the following for (j{n) :

o-(n)-2{o-(n-l)+o-(n-2)) +3{(7(n-3)+(r(n-4)+(7(n-5)! - . . .
+ (-irV{...+(r(l)) = (-l)V-s)/6,

where s = r unless ra-(l) is the last term of a group, in which case, s = r+l.
He proved Jacobi's^^ statement and concluded from the same proof that
E{n) =JlE{ni) if n=nn„ the n's being relatively prime. It is evident that
E{p')=r-\-l if p is a prime 4m+l, while £'(pO = l or 0 if p is a prime
4m+3, according as r is even or odd. Also £'(2'') = 1. Hence we can at
once evaluate E{n). He gave a table of the values oi E{n),n = \,. . ., 1000.
By use of elliptic functions he found the recursion formulae

E{n)-2E{n-^)+2E{n-\io)-2E{n-m)+ . . . =0 or (-l)'^-^^/^^,
for n odd, according as n is not or is a square; for any n.
E{n)-E{n-l)-E{n-S)+E{n-6)-{-E{n-10)- . . .

= 0 or (-ir{(-l)('-i)/2^-l}/4, ^^ Vs^^fl,

according as n is not or is a triangular number 1, 3, 6, 10, . . .. He gave
recursion formulae for

S{2n) =E(2)+E(4)+ . . . +E{2n),
S{2n-l)=E{l)-\-E{S)+ . . .+Ei2n-1).

The functions E, S, 6, a are expressed as determinants.
J. P. Gram^^" deduced results of Berger^^ and Cesaro.^'*
Ch. Hermite^^ expressed (T(l)+<r (3) + . • - +o-(2n-l), (t(3) +o-(7) + . . .

+o-(4n — 1) and o-(1)+<j(5)+ . . . +(7(4n+l) as sums of functions

E,{x)=^{[xf-^[x\]/2.

Chr. Zeller^^ gave the final formula of Catalan.^^

J. W. L. Glaisher®^ noted that, if in Halphen's^" formula, n is a triangular
number, (T{n—n) is to be given the value n/3; if, however, we suppress the
undefined term (7(0), the formula is

(T(n)-3(j(n-l)+5(7(n-3)- . . . =0 or {-lY-\l''+2''+ . . .+r''),

according as n is not a triangular number or is the triangular number
r(r+ 1)/2. He reproduced two of his^^'^"*'^^ own recursion formulas for
<T{n) (with yp for <j in two) and added

o-(n)-{(7(n-2)+o-(n-3)+(r(n-4)j + !(7(n-7)-f(r(n-8)+(7(n-9)

+o-(n-10)+(7(n-ll)[-{(T(n-15)+...) + ...=A-B,

«^Proc. London Math. Soc, 15, 1883-4, 104-122.

"°Det K. Danske Vidensk. Selskabs Skrifter, (6), 2 1881-6 (1884), 215-220 296.

"^Amer. Jour. Math., 6, 1884, 173-4.

6«Acta Math., 4, 1884, 415-6.

6Troc. Cambr. Phil. Soc, 5, 1884, 108-120.

296 History of the Theory of Numbers. [Chap, x

where A and B denote the number of positive and negative terms respec-
tively, not counting cr{0) =n as a term;

n<T(n)+2{(n-2)(r(n-2) + (n-4)(r(n-4)l

+3{(n-6)(r(n-6) + (n-8)(7(n-8) + (n-10)tr(n-10)} + ...
= a{n) + {V-+3')\a{n-2)+a{n-4:)]

+ (l-+3- + 5') {(r(n-6)+(r(n-8)+<r(n-10)l + ... (n odd).

He reproduced his^ formulas for d{n) and E{n). He announced {ibid., p. 86)
the completion of tables of the values of ^(n), T{n), (T{n) up to n = 3000, and
inverse tables.

Mobius^^ obtained certain results on the reversion of series which were
combined by J. W. L. Glaisher^^ into the general theorem: Let a,h, ...
be distinct primes; in terms of the undefined quantities e^, %,..., let e„
= e^V/ ... if n = a'^lP . . . , and let ei = 1. Then, if

F(a:)=SeJ(a:"),
where n ranges over all products of powers of a, 6, . . . , we have

/(x)=S(-l)^6^(a;0,

where v ranges over the numbers wdthout square factors and divisible by
no prime other than a, 6, ... , while r is the number of the prime factors of v.
Taking

Glaisher obtained the formula of H. J. S. Smith^^ and

aM -2aV,(^) +2a'fcV.(^^^ - . . . = 1.

Using the same/, but taking €2 = 0, Cp = p\ when p is an odd prime, he proved
that, if Ar{n) is the sum of the rth powers of the odd divisors of n,

A,(„)-.A,©-f.A,(|)

= 0 or rf,

according as n is even or odd. In the latter case, it reduces to Smith's.

If A'r(^) is the sum of the rth powers of those di\'isors of n whose com-
plementary divisors are odd, while Er{n) [or E'r{n)] is the excess of the sum
of the rth powers of those divisors of n which [whose complementary divisors]
are of the form 47?i + 1 over the sum of the rth powers of those divisors which
[whose complementary divisors] are of the form 4772+3,

A',(n)-2a'A',(^)+2a'6'A',(^^) - , . , =;, = ijl-(-l)-),
A',(„)-2A',Q+2A-,(^)-...=n-,

"Jour, fiir Math., 9, 1832, 105-123; Werke, 4, 591.
"London, Ed. Dublin Phil. Mag., (5), 18, 1884, 518-540.

Chap. X] SuM AND NUMBER OF DiVISORS. 297

EM -s^.(^) +s^.(£) - . . . = (-i)^"-^>/v.,

E'Xn) -^a^E\(^^ +^a%^E',{^^ -... =^{-\r-'^'\
E\{n)-U-ir-'"'E\{^ +S(-l)(^«-i)/2^;(^JL^ - . . . =n^

where A,B,. . . are the odd prime factors of n. Note that ^ = 0 or 1 according
as n is even or odd. By means of these equations, each of the five functions
(Tr{i^),- ■ -J E'r{n) is expressed in two or more ways as a determinant of
order n.

Ch. Hermite^° quoted five formulas obtained by L. Kronecker'^^ from the
expansions of elHptic functions and involving as coefficients the functions
$(n)=o-(n), the sum Z(n)_of the odd divisors of n, the excess ^(n) of the
sum of the divisors >\/n of n over the sum of those <\/n, the excess
$'(n) of the sum of the divisors of the form 8k=^l of n over the sum of the
divisors of the form 8k^S, and the excess ^'(n) of the sum of the divisors
8A;± 1 exceeding Vn and the divisors 8A;± 3 less than y/n over the sum of the
divisors Sk=i=l less than \/n and the divisors 8A;± 3 exceeding \/n. Hermite
found the expansions into series of the right-hand members of the five
formulas, employing the notations

Ei{x) = [a:+i] - [x], E^ix) = [x\[x+\]/2,

a = l, 3, 5,...; 6 = 2,4,6,...; c = l, 2, 3,...,

and A for a number of type a, etc. He obtained

Z(l)+X(3)+. . .+X(A)=SE2(^),
(r(l) +(7(2) + . . . + (7 (C) =SE2(C/c),

^(l)+^(2)+. . .+^(0=2^2 (^'),
X(2)+Z(4)+ . . . +Z(B) =is|a[^] +&^i[|]|
«l>'(l)+*'(3)+. . .+$'(A)=S(-l)^"^-^)/«a[^],
^'(l)+^'(3)+ . . . +^'{A) =S(-l)('^^+^>/«a| l^^+^^-^'j

"BuU. Ac. Sc. St. Petersbourg, 29, 1884, 340-3; Acta Math., 5, 1884-5, 315-9.
"Jour, fiir Math., 57, 1860, bottom p. 252 and top p. 253.

298 History of the Theory of Numbers. [Chap, x

The first three had been found and proved purely arithmetically by Lipschitz
and communicated to Hermite.

Hermite proved (11) by use of series. Also,

i F{a)=i r^l/(a), F(n)^2/(d),

a = l a = l LuJ

where d ranges over the di\'isors of n. When f{d) = I, F{n) becomes T{n)
and the formula becomes the first one by Dirichlet.^^

L. Gegenbauer"'- considered the sum p^. , (n) of the A:th powers of those
divisors d, of n whose complementary divisors are exact ^th powers, as well
as Jordan's function Jk{n) [see Ch. V]. By means of the f -function, (12), he
proved that

2 (Tk{m)po, 2(n) =2po. 2t{d)pk, t K j '

where d ranges over the divisors of r, and 7n, n over all pairs of integers for
which mv} = r',

2 Jtk{n)p,, t{m) = rV^jt. <(r) , 2 <T,_k{m)T{n)m'' ='Epk, t{d)p,, t \j) '

the latter for t = l being Liouville's^® seventh formula ioT v = 0;

2dV,(^) =2dV..(0, 2/.(d)dV.(0 =P.+.<(r),

the latter f or ^ = t- = 1 , A- = 0, being the second formula of Liouville"^, while for
< = 1 it is the final formula by Cesaro^^° of Ch. V;

2X(d)dV.,2.(0 =2X(d)p,.,((i)p*.,^0 =0 or P2k,t{\^),
according as r is not or is a square;

2X(n)p,. M =p,,2t{r), 2X(d)T(d2) =Hr)T{r),

^r\d)J,Q =r^^, 2dV(d2)(7,(0 =2dV(d),

2 \l\r{x') =2 At), 2 r^1x(x)(7,(x) =2 p^r).

2=iLa;J r=l i=lL3;J r=l

By changing the sign of the first subscript of p, we obtain formulas for the
sum Pk,i{n)=n''p_i,j{7i) of the A:th powers of those divisors of 7i which are
tth powers. By taking the second subscript of p to be unity, we get formulas
for (Tkin). There are given many formulas invohnng also the number
fain) of solutions of nin2. . .71^ = 71, and the number co(«) of ways n can be
expressed as a product of two relatively prime factors. Two special cases
[(107), (128)] of these are the first formula of Liou\ille-^ and the ninth
summation formula of Liouville,^^ a fact not observed by Gegenbauer. He
proved that, if p^n,

2 B{x) = - 2 Cix)-\-Bn-Ap,

i=p+l x = A + l

"Sitzungsber. Ak. Wiss. Wien (Math.), 89, II, 1884, 47-73, 76-79.

Chap. X] SuM AND Number of Divisors. 299

where

and B = B{n), A=B{p+l); also that

2 D{x)= S F{x)+Dn-Ep,

z=p+l x=D+l

where

and D = D(n), E = D(p-{-l). It is stated that special cases of these two
formulas (here reported with greater compactness) were given by Dirichlet,
Zeller, Berger and Cesaro. In the second, take t = 1, p = 0, and choose the
integers a, j8, b, n so that

hn''^-^>a>h{n-iy-\-^,

whence D = 0. If Xr is the number of divisors of r which are of the form
bx'+jS, we get

Change n to n + 1 and set i3 = 0, 6 = o- = l, whence a = n [also set p = [Vn]];
we get Meissel's^^ formula (11). Other speciaHzations give the last one
of the formulas by Lipschitz,^^ and

where v = [-\/n\, k{r) is the number of odd divisors of r, while ^ = 0 or 1
according as [n/v — ^]>v — \ or =v — \.

L. Gegenbauer'^^ proved by use of ^-functions many formulas involving
his'^^ functions p, / and divisors d<. Among the simplest formulas, special
cases of the more general ones, are

2(r,(d)d^=S(r,+x(0rf'=2(r^(0d^+\ Xn\d,) =SX(A),

mh)tx\d,) =Xfx\h), i:r{h')}x\d,) =Zd{h), 2m'(^)^(0 ='r(r'),

Xrid^Uh) =e{r), Xi/{d)J,(^^ ^^dMh),

summed for d, c?2, d^, where h = Vr/dg. Other special cases are the fourth
and sixth formulas of Liouville,^^ the first, third and last of Liouville.^^
Beginning with p. 414, the formulas involve also

oi,{n)^n'Ti {l + \/vt), n=ilp:\

1=1 1=1

"Sitzungsber. Ak. Wien (Math.), 90, II, 1884, 395-459. The functions used are not defined
in the paper. For his \pf,, ^, u, we write 0-^, r, e, where e is the notation of Liouville."

n"

300 History of the Theory of Numbers. [Chap, x

Beginning with p. 425 and p. 430 there enter the two functions

■.?,(i)-{© -'■'-}•

in which (A/p) is Legendre's symbol, with the value 1 or —1.

J. W. L. Glaisher^'* investigated the excess tr{n) of the sum of the rth
powers of the odd di\'isors of n over the sum of the rth powers of the even
divisors, the sum A'r(n) of the rth powers of those divisors of n whose
complementary divisors are odd, wrote f for f i, and A' for A'l, and proved

A'3(n)=nA'(n)+4A'(l)A'(n-l)+4A'(2)A'(n-2)+. . .+4A'(n-l)A'(l),
r3(n) = (2n-l)r(n)-4r(l)r(n-l)-4r(2)r(n-2)-...-4r(n-l)f(l),
nA'(n)=A'(l)A'(2n-l)-A'(2)A'(2n-2) + . . .+A'(2n-1)A'(1),

(-l)''-H(n)=A'(n)+8r(l)A'(n-2)+8f(2)A'(n-4) + . . .,
A'3(n)=7zA'(n)+A'(2)A'(2n-2)+A'(4)A'(2n-4) + . . .+A'(2n-2)A'(2),
-f3(7i)=3A(n)+4{A(l)A(n-l)+9A(2)A(n-2)+A(3)A(n-3)

+9A(4)A(n-4)+ . . . +A(n-1)A(1)) {n even),

2^-W2.+i(n)_[l,2r-l] [3, 2r-3] [2r-l, 1]

(2r)! l!(2r-l)!"^3!(2r-3)!'^""'^(2r-l)!l!'

where

b,?]=(7p(lK(2n-l)+(rp(3K(2n-3) + . . .+(Tp(2n-lK(l).

For n odd, f (n) =A'(n) =a{n) and the fourth formula gives

(/i-lM7i)=8{(7(lMn-2)H-r(2M7i-4)+(7(3Mn-6)+r(4Mn-8) + . . .).

Glaisher'''^ proved that

5o'3(n) — 6w(7(n) -\-(j{n)

= 12{(7(l)(7(7i-l)+o-(2)(r(n-2)+...+(7(n-l)(T(l)),
(r(l)(r(2n-l)+(r(3)(r(2n-3) + . . .+or(2n-l)(T(l)

=A'3(n)=|{cr3(2ii)-(T3(n)}.

The latter includes the first theorem in his^^ earUer paper.
Glaisher'^^ proved for Jacobi's^^ E{n) that

cr(2m + l)=E(l)E(4m + l)+£;(5)^(4w-3)+E(9)E(4w-7) + . . .
+£(4m + l)E(l),
E(0-2^(^-4)+2E(<-16)-2E(«-36) + . . . =0 (« = 8n+5),

(7(y)-2(r(y-4)+2(7(y-16)-2(7(y-36) + . . . =0 (y = 8n+7),

<t(w) +(t(?/- 8) H-(r(i/- 24) +(r(w- 48) + . . . =4{(r(w)+2(T(m-4)
+2(r(rn-16)+2(7(m-36)+. . .) (m = 2n + l, w = 8n+3),

and three formulas analogous to the last (pp. 125, 129). He repeated
(p. 158) his^'* expressions for A'3(n).

^^Messenger Math., 14, 1884r-5, 102-8.

"•Hbid., 156-163.

'•Quar. Jour. Math., 20, 1885, 109, 116, 121, 118.

r,,.,(n)=SM.(^|);''

Chap. X] SuM AND NuMBER OF DiVISORS. 301

L. Gegenbauer^^ considered the number Ti(k) of the divisors ^[\/n] of ^
and the number T2ik) of the remaining divisors and proved that

STi(/c)=5(log,n+2C)+0(V^),

^r^ik) =|(log,n+2C-2)+0(V^),

0(s) being ^° of the order of magnitude of s. He proved (p. 55) that the mean
of the sum of the reciprocals of the square divisors of any integer is 7rV90;
that (p. 64) of the reciprocals of the odd divisors is ttVS; the mean (p. 65)
of the cubes of the reciprocals of the odd divisors of any integer is 7r^/96,
that of their fifth powers is 7r^/960. The mean (p. 68) of Jacobi's^^ E{n) is
7r/4.

G. L. Dirichlet^^ noted that in (7), p. 282 above, we may take e to be of
lower [unstated] order of magnitude than his former -\/n-

L. Gegenbauer^^ considered the sum r^ k,s (n) of the kth powers of those
divisors of n which are rth powers and 'are divisible by no (sr) th power
except 1 ; also the number Qa{b) of integers ^ b which are divisible by no ath
power except 1. It follows at once that, if /Xg(^) =0 if m is divisible by an
sth power >1, but =1 otherwise,

where the summation extends over all the divisors dr of n whose com-
plementary divisors are rth powers, and that

(14) ST..,,(a;)= S -; hr^V.(^), v = Wn].

From.the known formula Qr{n) =S[n/a;'^]/z(x), x = 1, . . ., j^, is deduced

the right member reducing to n for A; = 0 and thus giving a result due to
Bougaief. From this special result and (14) is derived

From these results he derived various expressions for the mean value of
Tr,-k,s{^) and of the sum t^.aj.X^) of the A;th powers of those divisors of n
which are rth powers and are divisible by at least one (sr) th power other
than 1. He obtained theorems of the type: The mean value of the number
of square divisors not divisible by a biquadrate is 15/x^; the mean value of
the excess of the number of divisors of one of the forms 4rjLi+y(j = l, 3, . . .,
2r — 1) over the number of the remaining odd divisors is

1 i cot(2LdV.
4ri^i 4r

"Denkschr. Akad. Wien (Math.), 49, I, 1885, 24.

78G6ttingen Nachrichten, 1885, 379; Werke, 2, 407; letter to Kronecker, July 23, 1858.

"Sitzungsberichte Ak. Wiss. Wien (Math.), 91, II, 1885, 600-^21.

302 History of the Theory of Numbers. [Chap, x

L. Gegenbauer^" considered the number Ao{a) of those di\'isors of a
which are congruent modulo k and have a complementary divisor =1
(mod k). He proved that, if p<k,

If we replace (t by <t — 1 and subtract, we obtain expressions for Ao{k(T—p).
The above formulas give, for k = 2, p = l,

and formulas of Bouniakowsky.^^ The same developments show that an
odd number a is a prime if

L2(2a:+1) ^2j L2(2x+l)^2j

for x^[(a — Z)/2]; likewise for a = 6fc=*=l if the same equality holds when
x^[(a — 5)/Q], with similar tests for a = 3n — 1, or 4n — 1.

C. Runge^^ proved that T{n)/n* has the limit zero as n increases indefi-
nitely, for every e>0.

E. Catalan^- noted that, if x^p is the number of ways of decomposing a
product of n distinct primes into p factors >1, order being immaterial,

x„p = px„_ip+x„_i,_i = jp'-^-(PTi)(p-ir-^+(^-^)(p-2r-^-...±i}

-^{(p-l!).
E. Cesaro^ considered the number F„ (x) of integers ^x which are not
divisible by mth powers, and the number T^ (x) of those di\'isors of x which
are mth. powers, evaluated sums involving these and other functions, and
determined mean values and probabilities relating to the greatest square
divisor of an arbitrary integer.

R. Lipschitz^ considered the sum k{m) of the odd di\'isors of m increased
by half the sum of the even di\'isors, and the function l(m) obtained by
interchanging the words "even," "odd." He proved that

k{m)-2k{m-l)+2k{m-9)- . . . =(-1)"-'^ or 0,
according as m is a square or is not;

l{m)+l{m-l)+l{77i-S)+l{m-6)+. . . = -m or 0,
according as m is a triangular number or is not ;

XW=A'(1)+A'(2)+...+A-W = H+[|]+3[|]+2[^] + ...+m[^],
L(m) = /(l)+Z(2)+ . . . +l{m) = -[m]-^2[f\ -^[f\+^[f\ -■■■>

"Sitzunpsberichte Ak. Wien. (Math.), 91, II, 1885, 1194-1201. "Acta Math., 7, 1885, 181-3.
"M^m. 80C. roy. sc. Lifege, (2), 12, 1885, 18-20; Melanges Math., 1868, 18.
"Annali di Mat., (2), 13, 1885, 251-268. Reprint "Excursions arith. k Tinfini," 17-34.
"Comptes Rendus Paris, 100, 1885, 845. Cf. Glaisher"«, also Fergola" of Ch. XI, Vol. II.

Chap. X] SuM AND NuMBER OF DiVISORS. 303

where fx = m or m/2 according as m is odd or even. Cf . Hacks.^^

M. A. Stern^^ noted that Zeller's^^ formula follows from B=pA, where

1 00 n 00

= A= Si/'(n)a;", -^=S= S o-(n)a:'*-\ p = l+2a:-5x*-7x^+

pix) n=o V{x)

where p(rc) is defined by (1), yp{n) is the number of partitions of n, and
the second equation follows from the equality of (3) and (4) after remov-
ing the factor x. Next, if N{n) denotes the number of combinations of
1, 2, . . ., n without repetitions producing the sum n,

X N(n)x''= {l+x){l+x^) . . . =

2, (l-x')il-x')

rZi ^ ' ' ' '' '^■■- {l-x){l-x')...'
then by the second equation above,

B{\-x^-x'^x^''+x^^- . . .)=pSA^(n)x~,

(r(n)-o-(n-2)-o'(7i-4)+(r(n-10)+(7(n-14)- . . .
=i\r(n-l)+2i\r(n-2)-5iV(n-5)-7iV(n-7)+...,

where (T{n — n) =0, N{n—n) = 1.

S. Roberts^^ noted that Euler's^ formula (2) is identical with Newton's
relation S^n = S-n+i+S^n+2— ■ ■ ■ for obtaining the sum aS_„ of the (— n)th
powers of the roots of s = 0, where s and p are defined by (2). In p, the sum
of the ( — n)th powers of the roots of 1 —a:^ = 0 is A; or 0 according as k is or is
not a divisor of n. Hence the like sum for p is (r{n). [Cf. Waring^.] The
process can be applied to products of factors 1 —f(k)x^. His further results
may be given the following simpler form. Let 0„ be the sum of the even
divisors of n, and xpn the sum of the odd divisors, and set s„=0„+2i^„ if n
is even, s„= — 2i^„ if n is odd. By elliptic function expansions,

S2n + 8{s2n_itAi+3S2H-2'/'2+S2n-3'A3 + 3S2n-4^4+ • • • -hSiXf/ 2n-l] +12ni/^2n = 0,
S2n+l+8{s2„lAi+3S2„_l^2+ ■ • ■ +3SilA2n) +(4n + 2)l/'2n+l=0»

the coefficients being 1 and 3 alternately. He indicated a process for finding
a recursion formula involving the sums of the cubes of the even divisors and
the sums of the cubes of the odd divisors, but did not give the formula.
N. V. Bougaief^®" obtained, as special cases of a summation formula,
^{Sx+5-5i2u-iy}(Ti2x + l-u'' + u) = 0, S{n -3(7(t/)}P{n -o-(w)} = 0,

where P{n) is the number of solutions u, v of a{u) +(t(v) =n.

L. Gegenbauer^®'' proved that the number of odd divisors of 1, 2, . . ., n
equals the sum of the greatest integers in (n+l)/2, (n+2)/4, (nH-3)/6, . . .,
(2n)/(2n). The number of divisors of the form Bx—'yoil,...,nis ex-
pressed as a sum of greatest integers; etc.

J. W. L. Glaisher^^ considered the sum A^n) of the sth powers of the odd
divisors of n, the Hke sum Dsin) for the even divisors, the sum D',{n) of the

s^Acta Mathematica, 6, 1885, 327-8.
8«Quar. Jour. Math., 20, 1885, 370-8.
8««Comptes Rendus Paris, 100, 1885, 1125, 1160.
sebDenkschr. Akad. Wiss Wien (Math.), 49, II, 1885, 111.
8'Messenger Math., 15, 1885-6, 1-20.

304 History of the Theory of Numbers. [Chap, x

sth powers of the divisors of n whose complementary divisors are even,
the excess f ',(«) of the sum of the sth powers of the divisors whose com-
plementary'' di\'isors are odd over that when they are even, and the similar
functions'^ A'„ f „ a,. The seven functions can be expressed in terms of any
two:

where the arguments are all n. Since D\{2k) =(T,(k), we may express all the
functions in terms of a^n) and (TXn/2), provided the latter be defined to be
zero when n is odd. Employ the abbreviation 'EfF='S,Ff for

/(l)F(n-l)+/(2)F(n-2)+/(3)F(n-3) + . . .+/(n-l)F(l).

This sum is evaluated when/ and F are any two of the above seven functions
w^th s = 1 (the subscript 1 is dropped) . If

f{n)=aa(n)+^D'in), F(n) =aV(n)+/3'Z)'(n),

then

2/F = aa'2(T(r+(ai8'+a'/3)S(Ti)'H-/3iS'2i)'Z)'.

By using the first formula in each of two earUer papers,'^' '^ we get

12'Z(ja = 5(T2{n) —6na{n) -\-a{n) ,

122D'D' = 5Ds'(n)-dnD'{n)+D'in),

242o-D' = 2(r3(n) + (l-3n)(7(7i) + (l-6n)D'(n)+8Z)3'(n).

Hence all 21 functions can now be expressed at once linearly in terms of
0-3, Ds', (T and D'. The resulting expressions are tabulated; they give the
coefficients in the products of any two of the series 2f/(n)x", where/ is any
one of our seven functions ■vsithout subscript.

Glaisher^^ gave the values of l^a^ai for 2 = 3, 5, 9 and ^<r^(TT, where the
notation is that of the preceding paper. Also, if p = 7i—r,

12 S rpa{f)a{fi) ^n^a^in) -nV(n), S rj{r)F{p) =^/F.

r=l r=l A

L. Gegenbauer^^ gave purely arithmetical proofs of generalizations of
theorems obtained by Hermite'" by use of elliptic function expansions. Let

5,(r) =2/, (7=J^5,([^]) -v&,{y), v^\yM'

Then (p. 1059),

The left member is knowTi to equal the sum of the ^th powers of all the
divisors of 1, 2, . . ., n. The first sum on the right is the sum of the A-th
powers of the divisors ^ y/n of 1, . . . , n. Hence if A^fx) is the excess of the

"Messenp;er Math., 15, 188.5-6, p. 36.

'•Sitzungsberichte Ak. Wien (Math.), 92, II, 1886, 1055-78.

Chap. X] SuM AND NuMBER OF DiVISORS. 305

sum t/'fc'(a;) of the kth powers of the divisors > \/x of x over the sum of the
A;th powers of the remaining divisors, it follows at once that

Also

n V ['fi~\

x=l x=lL-CJ

^J,\x) =£'S^([3) +^''+M - (^+i)5,(.),

with a similar formula for ^^^(a;), where "^k(^) is the excess of xpki^) over the
sum of the A;th powers of the divisors < y/x of x. For k — l, the last formula
reduces to the third one of Hermite's.

Let Xk{^) be the sum of the kth powers of the odd divisors of x; Xk\^)
that for the odd divisors > \/x; Xk"{x) the excess of the latter sum over the
sum of the A;th powers of the odd divisors < ^/x of x; Xk"'{'^) the excess of the
sum of the kih. powers of the divisors 8s±l>\/x of x over the sum of the
kih. powers of the divisors 8s='=3<\/^ of ^- For y = 2x and y = 2x — l, the
sum from x = l to a: = n of Xkiv), Xk'iv), X/iy) and Xk"{y) are expressed as
complicated sums involving the functions Sk and [x\.

E. Pfeiffer^° attempted to prove a formula like (7) of Dirichlet/^ where
now e is 0{'n}^^^^) for every k>0. Here Og{T) means a function whose
quotient hy g{T) remains numerically less than a fixed finite value for all
sufficiently large values of 7". E. Landau^ ^ noted that the final step in
the proof fails from lack of uniform convergence and reconstructed the
proof to secure this convergence.

L. Gegenbauer,^^ in continuation of his^° paper, gave similar but longer
expressions for

S r{y), S (Tkiy) (2/ = 4a;+l, 6a;+l, 8a:+3, 8a:+5, 8a:+7)

and deduced similar tests for the primality of y.

Gegenbauer^^" found the mean of the number of divisors \x-\-a of a
number of s digits with a complementary divisor iiy-\-^; also for divisors
ax'^+hy'^.

Gegenbauer^^'' evaluated A(l) + . . . +A(n) where A{x) is the sum of the
pth powers of the crth roots of those divisors d oi x which are exact o-th
powers and whose complementary divisors exceed kdJ/'^. A special case
gives (11), p. 284 above.

Gegenbauer^^" gave a formula involving the sum of the A;th powers of
those divisors of 1, . . . , m whose complementary divisors are divisible by no
rth power >1.

'"Ueber die Periodicitat in der Teilbarkeit . . . , Jahresbericht der Pf eiffer'schen Lehr- und Erzieh-

ungs-Anstalt zu Jena, 1885-6, 1-21.
"Sitzungsber. Ak. Wiss. Wien (Math.), 121, Ila, 1912, 2195-2332; 124, Ila, 1915, 469-550.

Landau.^^^
»276id., 93, II, 1886, 447-454.

"-^Sitzungsber. Ak. Wiss. Wien (Math.), 93, 1886, II, 90-105.
92676id., 94, 1886, II, 35-40.
"^c/feid., 757-762.

306 History of the Theory of Numbers. [Chap, x 1 C^'

Ch. Hermite^' proved that if F{N) is the number of odd divisors of N,

n = l

and then that

F(l)+F(2)+ . . . +F{N) =^N log iV+ (c-^N,

$(l)+$(2)+ . . . +$(iV) =^N log N/k+ (c-^N,

asATnptotically, where ^(N) is the number of decompositions of N into two
factors d, d', such that d'>kd.

E. Catalan^^" noted that, if n = i+i' = 2i"d,

'La{i)a{i')=2(P, i:{aii)a{2n-i)} =Si:{<j{i)<x{n-i)].

E. Ces^ro^ proved Lambert's^ result that T{n) is the coefficient of x" in
2xV(l — a;*). Let T,{n) be the number of sets of positive integral solutions of

and s,{n) the sum of the values taken by ^,. Then

sM = TM + TXn-v) + TXn -2v)+...,
T{n) =Si(n) -Szin) +83(71)

Let aa^)=S(-l)'*+^r,(x-n),

summed for the divisors d of n. Then

Tin)=tM+t2{n)+ . . .+TM-T2{n) + Ts{n)- . . ..

E. Busche^^ employed two complementary di\isors 5^ and 8 J of m,
an arbitrary function/, and a function y=^(x) increasing with x whose
inverse function is x = ?/)/' (7/). Then

2 limx)], X) -/(O, x) } =2 {/(5'^, 5 J -/(5'^- 1, 5 J ) ,

x=l

where in the second member the summation extends over all divisors of all
positive integers, and $(w)^6;„^a. In particular,

2 /(x)[tA(x)] =2/(5J, 2 [rA(x)] = number of 5„,

1=1 2=1

subject to the same inequalities. In the last equation take \l/(x)=x,
a = [\/n]', we get (11).

J. Hacks^® proved that, if 7?i is odd,

^W^T(l)+r(3)+T(5) + . . . +r(7n) =2[^],

wjour. fur Math., 99, 1886, 324-8.

•"^Mdm. .Soc. R. Sc. Li^ge, (2), 13, 1886, 318 (Melanges Math., II).

•*Jomal de sciencias math, e astr., 7, 1886, 3-6.

«Jour. fiir Math., 100, 1887, 459-464. Cf. Busche.»"

"Acta Math., 9, 1887, 177-181. Corrections, Hacks, »^ p. 6, footnote.

Chap. X] SuM AND NUMBER OF DiVISORS. 307

@(m)=or(l)+(7(3)+(r(5) + . . .+(7(m)=S^[^^],

where t ranges over the odd integers ^ m. For the K and L of Lipschitz^
and G{m) =(r(l)+o-(2) + . . . -\-<T(m), it is shown that

LW^(?(m)^[Vm] + [^|], !r(m)^[v^] (mod 2).

J. Hacks^^ gave a geometrical proof of (11) and of Dirichlet's^^ expression
for T{n), just preceding (7). He proved that the smn of all the divisors,
which are exact ath powers, of 1, 2, . . . , m is

m

S{1^+2«+...+[a/^H.

3 = 1

He gave (pp. 13-15) several expressions for his^^ i^M, &(m), K{m).
L. Gegenbauer^^" gave simple proofs of the congruences of Hacks. ^^
M. Lerch^^ considered the number \p{a, h) of divisors >6 of a and proved

that

[n/2] n

(15) X \}/{n—p, p) =71, Si/'(n4-p, p)=2n.

p=0 p=0

A. Strnad^^ considered the same formulas (15).

M. Lerch^°° considered the number x(«j b) of the divisors ^6 of a and
proved that

[(m-l)/a]

S {\J/{m—aa,k+a)—xi'm—aa,a)]

<7 = 0

k

+ S {\J/{m+\a, X-l)-x(m+Xa, a)) =0.
x=i

This reduces to his (15) for a = l, k = l orm + 1. Let (k, n; m) denote the
g. c. d. {k, n) of k, n or zero, according as {k, n) is or is not a divisor of m.
Then

a— 1 a

(16) S {i/'(m4-an, a)— ;/'(m+an, a)] = S (A;, n; m).

In case m and n are relatively prime, the right member equals the number
0(a, n) of integers^ a which are prime to n. Finally, it is stated that

(17) S 1/^(772 — an, a) = S x(^ — ctn, n), c= .

a = 0 a = 0 L n J

Gegenbauer,^^ Ch. VIII, proved (16) and the formula preceding it.

"Acta Math., 10, 1887, 9-11.

"oSitzungsber. Ak. Wiss. Wien (Math.), 95, 1887, II, 297-8.
"Prag Sitzungsberichte (Math.), 1887, 683-8.
"Casopis mat. fys., 18, 1888, 204.
""Compt. Rend. Paris, 106, 1888, 186. Bull, des sc. math, et astr., (2), 12, 1, 1888, 100-108, 121-6.

308 History of the Theory of Numbers. [Chap, x

C. A. Laisant^"^ considered the number nk{N) of ways N can be expressed
as a product of k factors (including factors unity), counting PQ . . . and QP . . .
as distinct decompositions. Then

n,{N) =n,_,{N)u(l-\-^y N=Upr.

E. Ces^ro^"^ proved Gauss' result that the number of di\'isors, not
squares, of n is asymptotic to Gtt"^ logn. Hence T{n~) is asymptotic to
Stt"^ log^n. The number of decompositions of n into two factors whose
g. c. d. has a certain property is asymptotic to the product of log n by the
probability that the g. c. d. of two numbers taken at random has the same
property.

E. Busche^''^ gave a geometric proof of his^^ formula. But if we take
$(x) to be a continuous function decreasing as x increases, with $(0)>0,
then the number of positive divisors of y which are ^4^iy) is S[$(a:)/x],
summed for x = 1, 2, . . . , with $(x) ^ 0. This result is extended to give the
number of non-associated di\'isors of y+zi whose absolute value is ^4>{y, z).

J. W. L. Glaisher^^ considered the excess H{n) of the number of divisors
= 1 (mod 3) of n over the number of divisors =2 (mod 3), proved that
H{pq) =H{p)H{q) if p, q are relatively prime, and discussed the relation of
H{n) to Jacobi's^i E{n).

Glaisher^^^ gave recursion formulae for H{n) and a table of its values for
n = l,..., 100.

L. Gegenbauer^°^ found the mean value of the number of divisors of an
integer which are relatively prime to given primes pi, . . . , Pa, and are
also (pr) th powers and have a complementary divisor which is di\'isible
by no rth powers. Also the mean of the sum of the reciprocals of the A;th
powers of those di\'isors of an integer which are prime to pi, . . . , p„ and are
rth powers. Also many similar theorems.

Gegenbauer^o^" expressed S^=S i^(4.T+l) and SF(4a;+3) in terms of
Jacobi's symbols (A/?/) and greatest integers [ij] when F{x) is the sum of the
A;th powers of those divisors ^ -x/x of x which are prime to D, or are divisible
by no rih. power > 1, etc.; and gave asymptotic evaluations of these sums.

J. P. Gram^°^ considered the number D„(m) of di\dsors ^m of n, the
number iV"2, 3 ..(^) of integers ^n which are products of powers of the
primes 2, 3, . . , and the sum -Lo. 3. . . (n) of the values of \(k) whose arguments
k are the preceding N numbers, where X(2"3^ . . . ) = ( ~ 1)"+'^+ •.

If p = Pi°'P2°'. . ., where the p, are distinct primes,

Dj,{n) = Nin) -'LN(n/p,''^+') +SiV(n/pi"'+ ^2'^'^') - • • • •

""Bull. Soc. Math. France, 16, 1888, 150.
i^Atti R. Accad. Lincei, Rendiconti, 4, 1888, I, 452-7.
>MJour. fur Math., 104, 1889, 32-37.

"xProc. London Math. Soc, 21, 1889-90, 198-201, 209. ^°Hbid., 395-402. See Glaisher.'"

'»«Denkschi-iften Ak. Wiss. Wien (Math.), 57, 1890, 497-530.
'""'Sitzungsber. Ak. Wiss. Wien (Math.), 99, 1890, Ila, 390-9.

'"Det K. Danske Videnskab. Selskaba Skrifter (natur. og math.), (6), 7, 1890, 1-28, with r6-
8um6 in French, 29-34.

i

Chap. X]

Sum and Number of Divisors.

309

In particular, if the pi include all the primes in order, we may replace
N{x) by [x], the greatest integer ^x. Since there are as many divisors
>a of n as there are divisors <n/a,

D»+i),(^^^=€+n(a,+l),

where € = 1 or 0 according as n is or is not a divisor of p. These two formulas
serve as recursion formulas for the computation of N{n). For the case of
two primes pi = 2, p2 = 3,

The functions L satisfy similar formulas and are computed similarly.

J. W. L. Glaisher^"^ stated a theorem, which reduces for m = l to
Halphen's,4°

/S=o-^(n)-3o-^(n-l)+5o-^(n-3)-7(r„(n-6)+9(7^(n-10)-. . .
= 2s(^'^^{cr^_,(n-l)-(l^+2V^_,(n-3)+(lH2H3V^_,(n-6)-. . . j

provided m is odd, where k ranges over the even numbers 2, 4, . . ., ?n — 1,
while 6 = 0 or 6 = 1 according as n is not or is of the form g'(^ + l)/2. As in
Glaisher^^ for m = l, the series are stopped before any term (Ti{n — n) is
reached; but, if we retain such terms, we must set 6 = 0 for every n and
define o-i(O) by

m+2
m

©''^^'^^l^-^'+i^^'K

<r(0) =

©.;(o)=

m+2

B.

where Bi, B2, . . . are the Bernoullian numbers.

Glaisher^°^ stated the simpler generalization of Halphen'*":

'S+S 2Hk^(!k) f^-'^^'') -3^+V^_,(n-l)+5^+V_,(n-3) - . . . }

where the summation index k ranges over the even numbers 2, 4, ... , m — 1,
and m is odd. If we include the terms <T2,_i(0) = ( — !)' 5r/(4r) in the left
member, the right member is to be replaced by

5{-iy

2'"+2(m+2)

"^Messenger Math., 20, 1890-1, 129-135.
^o^Ibid., 177-181.

310 History of the Theory of Numbers. [Chap, x

Glaisher"" considered the set Gn[\l/(d), x(^>- •• ) of the values of \l/(d),
x(cO, • • • when d ranges over all the di\isors of n, and wrote —G{\J/, x,-)
for G{—\f/, — X, • •)• By use of the ^-function (12), he proved (p. 377) that
the numbers given by

GM-Gn-i(d, d=^l)+Gn-z{d, d^l, d=^2)-G,.M d^l, ^±2, ^±3) + . . .

all cancel if n is not a triangular number, but reduce to one 1, two 2's,
three 3's, . . ., g g's, each taken with the sign ( — )*~\ if n is the ^th tri-
angular number ^(gr+l)/2. For example, if n = 6, whence g = S,

{1, 2, 3, 6) - {1, 5; 2, 6; 0, 4} + {l, 3; 2, 4; 0, 2; 3, 5; -1, 1}

= {1,2,2,3,3,3).

Let \l/{d) be an odd function, so that \f/{ — d)=—\l/{d), and let 2r/(c?)
denote the sum of the values of f(d) when d ranges over the divisors of r.
Then the above theorem implies that

2„iA(d) -2„-i iHd) +4^{d=^ 1) ) +2„_i_2 [rPid) +rl^{d^ 1) -{-^p{d^ 2) )

-2„_i_2-3 {rpid) +yp{d^ 1) +iA(d± 2) +^(d± 3) 1 + . . .

= 5( - 1)''-^ {,^(1) +2^(2) +3V^(3) + . . . +g^l^{g) } ,

where 5 = 0 or 1 according as n is not or is of the form ^(^+l)/2, and where
\l/{d^i) is to be replaced by \}/{d+i)-{-yl/{d — i). Taking \l/{d) =d"', where m
is odd, we obtain Glaisher's^°^ recursion formula for (Tm{n), other forms of
which are derived. For the function^^ ^3, we derive

Un)+Un-1)+Un-S) + . . .+Q{nn-l)-{l'-2'mn-3)

+ (l2-22+3^)r(n-6)-...)
= (-l)''-^(l^-2H3'- . . . +(-l)'-y) or 0,

according as n is of the form ^(^+l)/2 or not.

Next he proved a companion theorem to the first :

2d-\-7 \,
-[2d-7];+

^/ 2d+l \ ^ / 2d+3 V^ / 2d+5 \ r f

all cancel if n is not a triangular number, but reduce to 1, 3, 5,. .., 2^ — 1,
each taken with the sign ( — )", together with ( — l)''+^(2^+l) taken g
times, if n is the gth triangular number ^(^+l)/2. For example, if n = 6,

{-tt J-;?}-{-t"M-3;-"}={-'-'-- ^- ^- ^}-

Hence if x(c^) be any even function, so that x(—d) = x{d),
2„{x(2d+l)-x(2d-l)l-2„_i{x(2ci+3)-x(2d-3)l+S„_3-....

= 5(-l)''-M^x(2^ + l)-x(l)-x(3)- . . . -x(2^-l)l.
Taking ^(A;) = fc'""*"\ where k and m are odd, we get Glaisher's^°^ formula.

"oProc. London Math. Soc, 22, 1890-1, 359-410. Results stated in London, Edinb., Dublin
Phil. Mag., (5), 33, 1892, 54-61.

I

Chap. X] SUM AND NuMBER OF DiVISORS. 311

He proved two theorems relating to the divisors of 1, 2, . . ., w:

+ (G^n-3 + ^n-4 + G^n-5)( _y_3l ) — • • •

all cancel with the exception of —2, — 4, . . ., — (p— 2), each taken twice,
p taken p — 1 times and — 0, if p be even; but with the exception of 1, 3, ... ,
p — 2, each taken twice, and —p taken p — 1 times, if p be odd, where
p(p+l)/2 is the triangular number next >n;

all cancel with the exception of k taken k times, for A; = 1, 3, 5, . . . , p — 1, if p
be even; and of —A; taken k times, for A; = 2, 4, 6, . . . , p — 1, if p be odd; here
zeros are ignored.

The last two theorems yield (as before) corresponding relations for any-
even function x aiid any odd function xp. Applying them to x{d+l)
= (d+l)"' and \l/{d)=d"*, where m is odd, and in the first case dividing
by 2(m+l), and modifying the right members, we get for

r=o-Jn)-2{(T^(n-l)+(r^(n-2)}+3{Mn-3)

+(rm{n-4:)+(Tm{n-5)]-. ..
the respective relations

+3*+^ (next three) - . . . }

-^-^M2(m^"^^^ +3 V2J^P -5V4/3"^ +...=^2 -p^,
where s = (m+l)/2 and 0-^(0) terms are suppressed;
!r=S2(^^{(r^_,(n-l)+(7^_fc(n-2)-2^ (next three) + ( 1^3') (next four)

_(2^+4*^) (next five) + (lH3*+5'=) (next six) - (2H4H6') (next seven) + . . . }
r ^m+i_^^m+i_^^m+i_^ _{_ (^ _ l)-+i^ if p bg eveu,

i-|_ 2^+1 _ 4^+1 _gm+i_ _(p_i)m+i^ if p be odd,

where, in each, A: takes the values 2, 4, . . . , m — 1. These sums of like powers
of odd or even numbers are expressed by the same function of Bernoullian
numbers. For m = l, the first formula becomes that by Glaisher,^^ repub-
Ushed.^^ Three further (t„ formulas are given, but not applied to o-„.
J. Hammond"^ wrote (n; m) = l or 0 according as n/m is integral or
fractional, also t{x) =a{x)=0 if x is fractional, and stated that

00 00

T(n/m) = S (n; jm), a (n/m) = 2 j(n; jm).
y=i }=i

"^Messenger Math., 20, 1890-1, 158-163.

312 History of the Theory of Numbers. [Chap, x

From the sum of Euler's (f}(d) for the di\'isors d of n, he obtained
a{n)=iT(jj<t>iJ), nr{n)=i<T(tjct>{j).

E. Lucas^^- proved the last formulas, the result of Cesaro/* and the
related one o-(n)+s„ = s„_i+2n — 1.

A. Berger"^ considered the mean of the number of decompositions of
1,2,. . ., X into three or more factors, and gave long expressions for \l/{l)-\-
.. .+^(7J), where i/'(A-) =2d'c?i*', summed for the solutions of ddi = k. He
gave (pp. 116-125) complicated results on the mean value of (Tk{n).

D. N. Sokolov and D. T. Egorov^^^" proved, by use of Bougaief's formu-
las for sums extending over all the divisors of a number, the formulas in
Liou\'ille's-°"'-^ series of four articles.

J. W. L. Glaisher^^"* gave Zeller's^^ formula and

P(n - 1) +2-P(n - 2) - 5-P(n - 5) - 7'P{n - 7) + . . .

= ^|5(r3(n)-(18n-lMn)l,

where 1, 2, 5, . . . are pentagonal numbers (3r=i=r)/2 and P(0) = 1.
Glaisher"^ proved formulae which are greatly shortened by setting

a./n)=n''(rXn)-3(n-l)V/n-l)+5(n-3)VXn-3)-7(n-6)'(T,(n-6)+....

Write Qij for ay(n). Besides the formula [of Halphen^°] aoi = 0, he gave

40
ao3-2an = 0, ao5-10ai3+ya2i = 0,

126 ,756 ^_ .

007 5~^15H H~^23 — 105031 = 0,

Oo9 - 50017+720025 - 336O033 +336O041 = 0,

with the agreement that o-(O) =n/3 and

— t--\-l f — 1 — ^'*+l t^—1

^3(0) = -24o-' <^M = -^' ^7(0)— ^^> <^9i0)=-^,

where t = Sn+l, but did not find the general formula of this type. Next,
he gave five formulas of another set, the first one being that of his earlier
paper,^ the second involving the same function of 0-3 with added terms in
ra{r). Finally, denoting Euler's formula (2) by Ea{n) =0, it is shown that

5Eas{n)-lSE{n(T{n)\ =0.

Glaisher^^^ showed that his"^ third formula holds for all odd numbers v
not expressible as a sum of three squares and hence in particular for the

"T'htorie des nombres, 1891, 403-6, 374, 388.

'"Nova Acta Soc. Upsal., (3), 14, 1891 (1886), No. 2, p. 63.

>"^Math. Soc. Moscow, 16, 1891, 89-112, 236-255.

"♦Messenger Math., 21, 1891-92, 47-8.

^''Ibid., 4^-69.

^*Ibid., 122, 126. The further results are quoted in the chapter on sums of three squares.

Chap. X] SUM AND NuMBER OF DiVISORS. 313

former case v=7 (mod 8). Also the left member of the third formula
equals

4jE(y-l)-3^(y-9)+5^(y-25)- . . .)

when V is odd, provided E{0) = 1/4. If A'(n) denotes the sum of those divi-
sors of n whose complementary divisors are odd,

A'(7i)-2A'(n-l)+2A'(n-4)-2A'(n-9)+. . . =0 or (-l)'^-^

according as n is not or is a square. [Cf. Lipschitz.^^] Since A'(n) =a{n)
for n odd, we deduce a formula involving c's and A"s.
M. Lerch"'' proved (11) and

if F{n) =2/(d), d ranging over the divisors of n.

K. Th. Vahlen^^^ proved Liouville's^^ formula and Jacobi's^" result.

A. P. Minin"^ proved that 2, 8, 9, 12, 18, 8g and 12p (where g is a prime
>2, p a prime >3) are the only numbers such that each is divisible by the
number of its divisors and the quotient is a prime. Minin^^° found that
1, 3, 8, 10, 18, 24 and 30 are the only numbers N for which the number of
divisors equals the number of integers < A^ and prime to A^.

M. Lerch^^^ considered the number x{a, b) and sum X{a, h) of the divisors
^b oi a, proved his^°° final formula (17) and

c c

a, X{m — a.n, a) = 2a{x(m — an, n)—yp{m — an, a)},

o=l a=l

(18) S \l/[m-an, ^) = 2 xim-an, rn), c=\ ^^-— •

a=o \ ^/ a=o L n J

If 6 ranges over the divisors of n,

i sV{(a-am, n)} =2^^^^, | sV|(a-am, n)\ =2(5, m) a),

't a=0 0 n a=0

S (am, n) =nS^-(5, (m, n)).

a=l 0

TO— 1

He quoted (p. 8) from a letter to him from Chr. Zeller that 2 a\p{m — a, a)

a=l

equals the sum of the remainders obtained on dividing m by the integers
<m.

M. Lerch^^^ proved that

'Zxf/im+p—crn, a) =2x(w+p— o-n, n) — 2 p \,

i:\pim-p-pn, a)=Xx{m-p-(rn, ^) -2[^:j:YjLn+fJ'

i^Casopis, Prag, 21, 1892, 90-95, 185-190 (in Bohemian). Cf. Jahrbuch Fortschritte Math.,

24, 1892, 186-7.
"sjour. fur Math., 112, 1893, 29.
i^Math. Soc. Moscow, 17, 1893, 240-253.
i2o/6id., 17, 1894, 537-544.
"iPrag Sitzungsberichte (Math.), 1894, No. 11.
^Ubid., No. 32.

314 History of the Theory of Numbers. [Chap, x

summed for p, o- = 0, 1, . . ., with p^<r. Also,

"s (-l)V(w-a,a)=2 2 (-l)"e'(/n-a) + (-l)'"m,

a-O a=0

m— 1 m PtwH

2^'(7n-a,a)=2(-l)*-Mf ,

a-O t = l L^J

2 Um-a, 2a) =m+^-ii- ^+2 2 (-1)' "^ ,

«=o ^ v=i L if J

where 6' (A") is the number of odd divisors of k; yp'{n, a) is the number of
div'isors >a of n whose complementary di\isors are odd; while \po{k, n) is the
number of even di\'isors >/i of k.

In No. 33, he expressed in terms of greatest integer functions

X{\p{7n—p—an, k-jr(T)—xi'm—p — (7n,n)}}
2{^(w — a, k-\-a) — {k-]-a)\l/{m — a, k-\-a)}-

a

E. Busche^^^ gave a geometrical proof of Meissel's^^ (11).
J. Schroder^^ obtained (11) and the first relation (15) of Lerch^^ as
special cases of the theorem that

0,1,2,... m m

2 \J/r,+sin-ri: ipi, 2p,)

Pi.--.Pm= » = 1 » = 1

equals the coefficient of x" in the expansion of

m-l

1- n (l-a:"+0

1=0

li::ri '

(l-x^"*) n(l-x"+0

t=0

where ypr,+>{o-j ^) is the number of di\isors of a which are >^ and have a
complementary divisor of the form rv-{-s{v = 0,l,. . .). He obtained

2 \f/r,+i{n-rp, p) = y J •

Schroder^^ determined the mentioned coefficient of x".
Schroder ^^^ proved the generaUzation of (11):

p=iLpJ p=iLpJ p=2 LpJ

For (j{\)-\- . . . +(r(n), Dirichlet," end, he gave the value

E. Busche^^^ proved that if X = 4)(m) is an increasing (or decreasing)
function whose inverse function is m=<l>(X), the divisors of the natural

i»Mittheilungen Math. GeseU. Hamburg, 3, 1894, 167-172.
"*Ibid., 177-188.
^Ibid., 3, 1897, 302-8.
"•/feid., 3, 1895, 219-223.
"Ubid., 3, 1896, 239-40.

Chap. X] SuM AND NuMBEK OF DiVISORS. 315

numbers between <^(m) and a, including the limits, are the numbers x from
1 to o (or those ^a) each taken ^= [$(x)/x] times, and the numbers within
the limits which are multiples of x are x,2x,. . ., ^x. For example, if a = 3,
</)(m)=900/m^, then <I>(a;)=30/Vx and it is a question of the divisors of
3. . ., 17; for x = 'd, ^ = 5 and 3 is a divisor of 3, 6, 9, 12, 15. For«I>(x)=n,
a = l, the theorem states that among the divisors of 1,. . ., n any one x
occurs [n/x] times and that these divisors are l,...,7i;l,..., [n/2]; 1,. . .,
[w/3]; etc. Hence the sum of the divisors of 1, . . . , n is

and their product is

n3.[n/x]=n[nA]!.

x=l x=\

He proved (pp. 244-6) that the number of divisors =r (mod s) of 1, 2, . . . , n
equals A-\-B, where A is the number of integers [n/x] for x = \,. . ., n
which have one of the residues r, r+l,...,s — 1 (mod s), and B is the number
of all divisors of 1, 2, . . . , [n/s\. The number of the divisors b of m, such that

\ n

n

and such that 5" divides m/8, equals the number of divisors of 1, 2, . . ., n.
The number of primes among n, [n/2], . . ., [n/n] equals the number of those
divisors of 1, . . ., n which are primes decreased by the number of divisors
which exceed by unity a prime.

P. Bachmann^^^ gave an exposition of the work of Dirichlet,^^' ^^ Mer-
tens,^'^ Hermite,^^ Lipschitz,^^ Ces^ro,^'' Gegenbauer,'^'^ Busche,^^^' ^"
Schr6der.i24. 126

N. V. Bougaiefi29 stated that

where d ranges over the divisors > 1 of n, and v = [Vn] ;

-i^HMM'

where d ranges over the divisors of n for which d <n. If 6 is any function,

nZ-^d{d)= Xi:d{d),

a y=i d

where, on the left, d ranges over all the divisors of n; on the right, only over
those ^ [nVj]. For 6{d) = l, this gives

„a(n) = Sx(n,[y]).

"8Die Analytische Zahlentheorie, 1894, 401-422, 431-6, 490-3.

i^'Comptes Rendus Paris, 120, 1895, 432-4. He used $ (a, 6), ^(a, b) with the same meaning
as xib, a), X{b, a) of Lerch,"^ and fi(n) for (r{n).

316 History of the Theory of Numbers. [Chap, x i>^

M. Lerch"° proved relations of the type

The number of solutions of [n/ x] = [n/ (x-\-l)], x<n, is

2i/^(n-r, r)+2 x{n-p, p) (A:= -§ + Vn + 1/4 ).

F. NachtikaP^^ gave an elementary proof of (15).
M. Lerch^^' proved that

2 \yp{vi—aa,-)-]r'4^{m—(Ta,ra)\

remains unaltered if we interchange r and s. He proved (18) and showed
that it also follows from the special case (17) . From (17) f orn = 2 he derived

L. Gegenbauer^^^" proved a formula which includes as special cases four
of the five general formulas by Bougaief .^^^ When x ranges over a given set S
of n positive integers, the sum2/(x)[x(a:)] is expressed as sums of expressions
$(p) and <J>i(p), where p takes values depending upon x, while $(2) is the sum
of the values of /(x) for x in *S and x^z, and $1(2) is the analogous sum with

X'^Z.

F. RogeP^^ differentiated repeatedly the relation

|x|<l,

00

n(i-

-xr''-'=e-^,

then set

a: = 0 and found that

22 -

(-1)''

\<T^{2)\^ Jcr

.(r)l

r'=ss(

-!)■/

the summations extending over all sets of a's for which

CI1+CI2+ . . . +ar = i, ai+2a2+ . . . -\-ra.r = r.

Starting with the reciprocals of the members of the initial relation, he
obtained similarly a second formula; subtracting it from the former result,
he obtained

.„(r)=."+|22{nf^+^;^-i)-(-i)'np}

ai!. . .a,_3!;=2l j J

""Casopis, Prag, 24, 1895, 25-34, 118-124; 25, 1896, 228-30.

"i/Wd., 25, 1896, 344-6.

»«Jornal de Scienciaa Math, e Astr. (TeLxeira), 12, 1896, 129-136.

"^'Monatshefte Math. Phys., 7, 1896, 26.

i»Sitzung8ber. Geaell. Wiss. (Math.), Prag, 1897, No. 7, 9 pp.

'y-'.J

Chap. X] SuM AND NuMBER OF DiVISORS. 317

where i = 3, 5, 7,. . . in S', while the a's range over the solutions of
ai+. . .+ar-3 = i, ai+2a2+. . . +(r-3)a,_3 = r.

The case n = 0 leads to relations for T{r).

J. de Vries^^^" proved the first formula of Lereh's.^^'^

A. Berger"^ considered the excess \l/{k) of the sum of the odd divisors of k
over the sum of the even divisors and proved that

xl/{n)+x{/in-l)+\l/{n-3)+x(/{n-Q)+xl/in-10)+ . . .=0 orn,

according as n is not or is a triangular number; also Euler's (2).
J. FraneP^^ employed two arbitrary functions /, g and set

d{n) ^Xmg( fj, F{n) = ifU), G{n) = S gU),

where d ranges over the divisors of n. Then

id{j) = 2 /(r)G[^] +^j(r)F\j] -F{v)G{v),

where v = ['\^n]. The case f{x)=g(x) = l gives Meissel's^" (11). Next, he
evaluated St?(j), where ??(n) =Xf{x)g{y)h(z), sunmied for the sets of positive
integral solutions of xyz = n. In particular, ■d(n) is the number of such sets
if f=g = h = l. Using Dirichlet's series, it is shown (p. 386) that

2^(i) = Si(logn+3C-l)2-3C2+6Ci+l}+e,

where e is of the order of magnitude of nP^^ log n, C is Euler's constant and
Ci = 0.0728 . . . [Piltz,^2 Landau^"].
FraneP^^ proved that

2^ = 1 log' P+2C log p+e+Ao,
r=i r

where Aq is a coefficient in a certain expansion, and ep^^^ remains in absolute
value inferior to a fixed number for every p.

E. Landau ^^'^ gave an immediate proof of (11) and of

S7^3(^)=2T(.)r-l

y = l u=l Li'J

where T^iv) is the number of decompositions of v into three factors. He
obtained by elementary methods a formula yielding the final result of

R. D. von Sterneck^^^" proved Jacobi's^^ formula for s^.

i33aK. Akad. Wetenschappen te Amsterdam, Verslagen, 5, 1897, 223.

i3*Nova Acta Soc. Sc. UpsaUensis, (3), 17, 1898, No. 3, p. 26.

"^Math. Annalen, 51, 1899, 369-387.

i3676id., 52, 1899, 536-8.

i"/6ici., 54, 1901, 592-601.

i^^Sitzungsber. Ak. Wiss. Wien (Math.), 109, Ila, 1900, 31-33.

318 History of the Theory of Numbers. [Chap, x

J. Franel"^ stated that, if /(n) is the number of positive integral solutions
of x''y^ = n, where a, h are distinct positive integers,

2/(r) =^i^l)n^+^{^n'+o{n'-^

+6J,

where'" 0{s) is of the order of magnitude of s. Taking a = l, 6 = 2, we see
that /(n) is the number of di\isors of q, where <f is the greatest square divid-
ing n, and that the mean of /(n) is tt"/ 6.

E. Landau^^^ proved the preceding formula of Franel's.

EUiott^^ of Ch, V gave formulas involving a{n) and rin).

L. Kronecker^'*'^ proved that the sum of the odd divisors of a number equals
the algebraic sum of all its di\isors taken positive or negative according as
the complementary^ di\'isor is odd or even (attributed to Euler^); proved
(pp. 267-8) the result of Dirichlet'^ and (p. 345) proved (7) and found the
median value (Mittelwert) of T{n) to be log^ n+2C with an error of the order
of magnitude of n~^^^when the number of values employed is of the order of
n^''^. Calling a di\isor of n a smaller or greater di\dsor according as it is less
than or greater than \/n, he found (pp. 343-369) the mean and median value
of the sum of all smaller (or greater) di\'isors of 1, 2, . . . , A^ [cf. Gegenbauer^^],
the sum of their reciprocals, and the sum of their logarithms. The mean of
Jacobi's^^ E{n) is x/4 (p. 374).

J. W. L. Glaisher^^^ tabulated for n = l,..., 1000 the values of the
function^'^ H{n) and of the excess J{n) of the number of divisors of n which
are of the form 8A- + 1 or 8A;+3 over the number of divisors of the form
8A:+5 or 8A:+7. WTien n is odd, 2J{n) is the number of representations of n
by x'-\-2f.

J. W. L. Glaisher"^ derived from Dirichlet's^^ formula, and also inde-
pendently, the simpler formula

2 0.(s) = -pG(p)+f[5],(.)+£(?{g]},

where p = {\/n]. The case g{s) = l gives Meissel's^- formula (11), which is
applied to find asymptotic formulae involving n/s — [n/s]. The error of the
approximation (7) is discussed at length (pp. 38-75, 180-2). The first
formula above is applied (pp. 183-229) to find exact and asymptotic formu-
las for 2/(s), when/(n) is Jacobi's" E{n), Glaisher's^^^ H{n) or J{n), or the
excess D{n) of the number of odd divisors of n over the number of even
di\'isors, or more general functions (p. 215, p. 223) involving the number of
di\isors with specified residues modulo r.

G. Voronoi^^^ proved a formula like Dirichlet's^^ (7), but with e now of the
same order of magnitude as -^/n log^ n.

•"L'intermddiaire des math., 6, 1899, 53; 18, 1911, 52-3.

"»/6ui., 20, 1913, 155.

•"Vorlesungen iiber Zahlentheorie, I, 1901, 54-55.

"'Messenger Math., 31, 1901-2, 64-72, 82-91.

>«Quar. Jour. Math., 33, 1902, 1-75, 180-229.

'«Jour. fiir Math., 126, 1903, 241-282.

Chap. X] SuM AND NUMBER OF DiVISORS. 319

H. Mellin"^ obtained asymptotic expressions for2T(n), So-(n).
I. Giulini^^^ noted that, if m and h are given integers, and /3(r) is the sum
of the divisors d = mk-\-h of r, then

i8(l) + . . .+/3(n)=2:4n/d], A; = 0, 1,. . ., [{n-h)/m],

k

The number and sum of the divisors d='mk-\-h oil,. . ., n are

[(n-w«]r^-i [n/im+h)] /^-hA , ,%'^\-n-sh , ,-|

S hj ' ^ 2 Eal ]+hi:\ +1 h

fc=o LttJ r=i \ mr / s=iL ms J

respectively, where ^2(2^) = W[a^+l]/2.

G. Voronoi^^^" gave for T{x) the precise analytic expression

x(logx+2(7-l)+i+Ma^)-2| g{t)dt^ {g{-x+ti)-g(-x-U)}idt,

and (p. 515) approximations to these integrals, where

,(x)= -i log .-iC-!2i^+2^ i^x(») ,og5(^+-i-).

He discussed at length the function g{x) and (pp. 467, 480-514) the asymp-
totic value of Sr(n)(x — 7i)V^!-

J. Schroder^^® proved that the sum of the I'th powers of 1, . . . , n is

S pf-1 =n(T._i(n)+ "S p'+ r pT ^1,
p=i LpJ p=t+i P=i LPJ

where t = [n/2], and the accent on the last S denotes that the summation
extends only over the values ^ ^ of p which are not divisors of n.

E. Busche^*^ proved that, if we multiply each divisor of m by each divisor
of n, the number of times we obtain a given divisor a of mn is Tiixv/a), where
jjL is the g. c. d. of m,a, and v is that of n, a. A like theorem is proved for
th^ divisors of mnp .... He stated (p. 233; cf. Bachmann^^^) that

(Th{m)(Th{n) =SdV;,f ^j,

where d ranges over the common divisors of m, n.

C. Hansen ^^^ denoted by Ti{n) and T^{n) the number of divisors of n
of the respective forms 4/c — 1 and 4/^ — 3, and set

A„=r3(4n-3)-ri(4n-3).

By use of Jacobi's B^{v, s) for ^ = 1/4, he proved that

„=i '^^ ~Zx^ ^ l-s'^"-^ l-2s^+2s^«+...

i«Acta Math., 28, 1904, 49.

i«Giornale di mat., 42, 1904, 103-8.

i^'^Annales sc. I'ecole norm, sup., (3), 21, 1904, 213-6, 245-9, 258-267, 472-480. Cf. Hardy.i^"

"«Mitt. Math. GeseU. Hamburg, 4, 1906, 256-8.

"V6id., 4, 1906, 229.

"^Oversigt K. Danske Videnskabemes Selskabs Forhandlinger, 1906, 19-30 (in French).

320 History of the Theory of Numbers. [Chap, x

and hence deduced the law of a recursion formula for A„. The law of a
recursion formula for B„ = 4{T2{7i) — Ti{n)\ is obtained from

S ^y S s''"+'^' cos(2n+l)^= i; (2n+l)s<2n+i)'sijj(2n+l)7,

n=0 n=0 4 n=0 4

with Bo=l, which was found by use of Jacobi's d{\, s). Next,

is shown to satisfy the functional equation

$(ts)=lj$(s)-$(-s)}-$(s2)+2$(s*).

If a convergent series liens'" is a solution $(s) of the latter, the coefficients are
uniquely determined by the C4i_3(/j = 1, 2, . . . ), which are arbitrary. Hence
the function 5„ is determined for all values of n by its values forn = 4/c— 3

(A: = l, 2,...).

S. Wigert^^^ proved that, for sufficiently large values of n, r(n)<2',
where f = (l + e) log n^-log log n, for every e >0; while there exist certain
values of n above any limit for which riri) >2', s = (1 — e) log n -i-log log n.

J. V. Pexider^^° proved that, if a, n are positive, a an integer,

by the method used, for the case in which n is an integral multiple of a,
by E. Cesaro.^° Taking a = [Vn], we have the second equation (11). Proof
is given of the first equation (11) and

S.[g=2.W, 2[2][!^]=S<?-.W,

where d ranges over the divisors of [n].

0. Meissner^" noted that, if m =pi". . .p/", where pi is the least of the
distinct primes pi, . . . , 7?„, then

,=iPj — 1 m ,=2Pt — 1 w log m

where G is finite and independent of m. If /v> 1, (Tk{m)/rn!' is bounded.

W. Sierpinski^^^ proved that the mean of the number of integers whose
squares divide n, of their sum, and of the greatest of them, are

x^ 1, .3^ 3 , , 9C , 36 - logs

— , -logn+^C, -:2lognH — rA — -^Z ^^,

respectively, where C is Euler's constant.

J. W. L. Glaisher^^^ derived formulas differing from his^^° earlier ones
only in the replacement of d by { — lY~^d, i. e., by changing the sign of each

"»Arkiv for mat., ast., fys., 3, 1906-7, No. 18, 9 pp.

»"Rendiconti Circolo Mat. Palermo, 24, 1907, 58-63.

"'Archiv Math. Phys., (3), 12, 1907, 199.

"^prawozdania Tow. Nank. (Proc. Sc. Soc. Warsaw), 1, 1908, 215-226 (Polish).

i"Proc. London Math. Soc, (2), 6, 1908, 424-^67.

Chap. X] SuM AND NuMBER OF DiVISORS. 321

even divisor d. In the case of the theorems on the cancellation of actual
divisors, the results follow at once from the earlier ones. But the recursion
formulae for o-„ and f „ are new and too numerous to quote. Cancellation
formulas (pp. 449-467) are proved for the divisors whose complementary-
divisors are odd, and applied to obtain recursion formulae for the related
function A/(n) of Glaisher.''^' "

E. Landau ^^^ proved that log 2 is the superior limit for x= oo of
log T(x)-log log a;-^log X.

M. Fekete^^^ employed the determinant RkX obtained by deleting the
last t rows and last t columns of Sylvester's eliminant of x'^— 1 = 0 and
a;"-l = 0. Set, for A;^n,

Then 6„(A;) = 1 or 0 according as k is or is not a divisor of n; while c„(i, k) = l
if ik = n and i is relatively prime to k, but = 0 in the contrary cases. Thus

T(n)=S6„(fc), (T{n)=ikK{k),

k = \ A: = l

while the number and sum of those divisors d of n, which are relatively prime
to the complementary divisors n/d, equal, respectively,

n 1 "

S Cn{i, k), - i: (i+k) c^{i, k).

i, k = \ ^ i,k = l

J. Schroder^" deduced from his^^"* final equation the results

The final sum equals XIZI i//(s, [s/{r+l)]).

P. Bachmann^^^ gave an exposition of the work of Euler,^'^ Glaisher,^^' ^^
Zeller,66 stern,^^ Glaisher,iio Liouville.^^

E. Landau ^^^ proved that the number of positive integers^ a; which have
exactly n positive integral divisors is asymptotic to

Aa;^/^^-^^(log log rr)'"-Vlog x,

where p is the least prime factor of n, and p occurs exactly w times in n,
while A depends only on n.

K. Knopp^^" obtained, by enumerations of lattice points,

n n w w

i:Mq,k)= i:hik,q)= i:f,iq,k)+i:f2{k,q)-F{w,w),

k=l k=l k=l k=l

where q = [n/k] and

/i(r, k)=k fij, k), h{k, s)=i f{k, j), F(r, s)=i Mr, j).
y=i y=i i=i

i66Handbuch. . .Verteilung der Primzahlen, I, 1909, 219-222.

i^^Math. 6s Phys. Lapok (Math. phys. soc), Budapest, 18, 1909, 349-370. German transl.,

Math. Naturwiss. Berichte aus Ungarn, 26, 1913 (1908), 196-211,
>"Mitt. Math. Gesell. Hamburg, 4, 1910, 467-470.
issNiedere Zahlentheorie, II, 1910, 268-273, 284-304, 375.
i^Annaes So. Acad. Polyt. do Porto, Coimbra, 6, 1911, 129-137.
""Sitzungsber. Berlin Math. Gesell., 11, 1912, 32-9; with Archiv Math. Phys.

322 History of the Theory of Numbers. [Chap, x

Taking /(/j, k) = l, we obtain Meissel's" (11), a direct proof of which
is also given. Taking /(/i, k)=f{h)g{hk), we get

S S/0>(j/c)=S/(/c)S^(iA:),

-m- I

special cases of which yield niany known formulas involving Mobius's func-
tion ju(n) or Euler's function (f>{n).

E. Landau^^^ proved the result due to PfeifTer^°, and a theorem more
effective than that by Piltz^^, having the 0 terms replaced by 0{x°-), where,
for every e>0,

k-1 .

E. Landau^^- extended the theorem of Piltz^^ to an arbitrary algebraic
domain, defining Tk{n) to be the number of representations of n as the norm
of a product of k ideals of the domain.

J. W. L. Glaisher^^, generalizing his^^^ formula, proved that

Sf[^]^(s)=Sf[^]^(s) + 2g[^]/(s)-F(p)G(p),

where F(s) =/(!)+ . . . +/(s), G{s)=g{l)+. . . -\-g{s), p = [v^]. A similar
generalization of another formula by Dirichlet^^ is proved, also analogous
theorems involving only odd arguments.

Glaisher^^ applied the formulas just mentioned to obtain theorems on
the number and sum of powers of divisors, which include all or only the
even or only the odd divisors. Among the results are (11) and those of
Hacks.^®'^^ The larger part of the paper relates to asymptotic formulas
for the functions mentioned, and the theorems are too numerous to be
cited here.

E. Landau^^ gave another proof of the result by Voronoi^^^. He proved
(p. 2223) that T(n)< 471^/^

J. W. L. Glaisher^^^ stated again many of his^^ results, but without
determining the limits of the errors of the asymptotic formulas.

S. Minetola^^^ proved that the number of ways a product of m distinct
primes can be expressed as a product of n factors is

iy{»"-G)("-')"+(2)(»-2)"--(„:ii)4

T. H. GronwalP^^ noted that the superior limits for a:= oo of
aM/x" (a>l), (r{x)/{x\oglogx)

are the zeta function f (a) and e^, respectively, C being Euler's constant.

"'Gottingen Nachrichten, 1912, 687-690, 716-731.

"»Tran8. Amer. Math. Soc, 13, 1912, 1-21.

»«Quar. Jour. Math., 43, 1912, 123-132.

^**Ibid., 315-377. Summary in Glaisher.i«

'"Messenger Math., 42, 1912-13, 1-12.

i««Il Boll, di Matematica Gior. Sc.-Didat., Roma, 11, 1912, 43-46; cf. Giomale di Mat., 45, 1907,

344-5; 47, 1909, 173, §1, No. 7.
"Trans. Amer. Math. Soc, 14, 1913, 113-122.

Chap. X] SuM AND NuMBEE OF DiVISORS. 323

P. Bachmann^^^ proved the final formula of Busche.^^'
K. Knopp^^^ studied the convergence of 26„a:V(l — 2:"), including the
series of Lambert^, and proved that the function defined in the unit circle
by Euler's^ product (1) can not be continued beyond that circle.

E. T. BelP'° proved that, if P is the product of all the distinct prime
factors of m, and X is their number, and d ranges over all divisors of m,

6^Sr(d)T(^^ =r{m)T{Pm)T{P''m).

J. F. Steffensen^'^^ proved that,^° if Ix denotes log x,

S. Wigert^^^ proved, for the sum n's{n) of the divisors of n,

(1 — €)e^ log log n< s{n) < {l-\-e)e^ log log n,
^s{n) = '^x-^l^{x), rP{x) = x^ 1 + 2 Ip(^),

for €> 0 and p{x)=x — [x]. For x sufficiently large,

(i-e) log x<xP{x)<(l+e) log x.
Besides results on Ss(a^)(x— n)*, lls{n) log x/n, he proved that

X ns{n)=^+xlh\ogx-rP{x)}+0{x).

E. Landau^^^ gave corrections and simplifications in the proofs by
Wigert."2

E. T. Bell^^^ introduced a function including as special cases the functions
treated by Liouville,^^"-^ restated his theorems and gave others.
J. G. van der Corput^^^ proved, for ix(d) as in Chapter XIX,

Sd'')u(d)So-„(A;)=x.
S. Ramanujan^'^® proved that t{N) is always less than 2* and 2', where^"

^ = lWV+« { (IsSpf '=^*-('°^ ^)+^f'°« iVe— .-!,

for Li(x) as in Ch. XVIII, and for a a constant. Also, t(N) exceeds 2*'and
2' for an infinitude of values of N. A highly composite number N is one
for which TiN)>T{n) when N>n', if Ar = 2''^3"». . .p"p, then aa^as^ag^

"SArchiv Math. Phys., (3), 21, 1913, 91.

"9Jour. flir Math., 142, 1913, 283-315; minor errata, 143, 1913, 50.

""Amer. Math. Monthly, 21, 1914, 130-1.

i"Acta Math., 37, 1914, 107. Extract from his Danish Diss., "Analytiske Studier med Anven-

delser paa Taltheorien," Kopenhagen, 1912.
"HUd., 113-140.

"^Gottingsche gelehrte Anzeigen, 177, 1915, 377-414.
"<Univ. of Washington PubUcations Math. Phys., 1, 1915, 6-8, 38-44.
'"Wiskundige Opgaven, 12, 1915, 182-4.
"oProc. London Math. Soc, (2), 14, 1915, 347-409.

324

History of the Theory of Numbers.

[Chap. X

. . . ^flp, while ap= 1 except when A'' = 4 or 36. The value of X for which
a2>ai> . . . >ax is investigated at length. The ratio of two consecutive
highly composite numbers A'' tends to unity. There is a table of A"s up
to t{N) = 10080. An N is called a superior highly composite number k
there exists a positive number e such that

N.^

N' = Ni^

for all values of A^ and No such that A'2> A'> A^i. Properties of t{N) are
found for (superior) highly composite numbers.

Ramanujan^" gave for the zeta function (12) the formula

and found asjTnptotic formulae for

j=i

S r'(j),
=1

Sr(jr+c),

S(7„(j>i(i),

A(n),

for a = 0 or 1 , where

A(n) = S^r(i.) =SM(d)r (0Z),(^),
summed for the di\isors d of v. If 5 is a common di\isor of u, v,
xM=iMW.g)rg)=2.W.@x(0.

E. Landau^'^^'' gave another asjinptotic formula for the number of de-
compositions of the numbers ^ x into k factors, A' ^ 2.
Ramanujan^'* wrote c^O) =^^("5) and proved that

2,,(,>.(n-,) ^^Pm^ ■ ^^l^lV

J=0

r(r+s + 2) f(r+s+2) ^^+*+^

r(i-r)+r(i-^)

(n)

/Z(r,+,_i(n)+0(n2'^+«+^^/^),

for positive odd integers r, s. Also that there is no error term in the right
member if r=l, s = 1, 3, 5, 7, 11; r = 3, s=3, 5, 9; r = 5, s = 7.

J. G. van der Corput^"^ wrote s for the g. c. d. of the exponents ai, a-z,...
in m='n.pi''i and expressed in terms of zeta function f(i), i=2, . . ., k-\-l,

2 {a,{s)-l]/m

m=2

if A' > 1 ; the sum being 1 — CifA=— 1, where C is Euler's constant.

"'Messenger Math., 45, 1915-6, 81-84.
"'"Sitzungsber. Ak. Wiss. Miinchen, 1915, 317-28.
i^Trans. Cambr. Phil. Soc, 22, 1916, 159-173.
"•Wiskundige Opgaven, 12, 1916, 116-7.

Chap. X] SuM AND NUMBEK OF DiVISORS. 325

G. H. Hardy^^° proved that for Dirichlet's^^ formula (7) there exists a
constant K such that e > Kn^^'^, e < — Kn^^'^, for an infinitude of values of n
surpassing all limit. In Piltz's^^ formula

S Tk{n) = x{akii\og xy-'-\- . . . -^-a^k} +e„

n=l

ek>Kx\ ik<—Kx\ where t={k — \)/{2k). He gave two proofs of an
equivalent to Voronoi's^^^'' explicit expression for T{x).

Hardy^^^ wrote A(n) for Dirichlet's e in (7) and proved that,^° for every
positive e, /l{n) = 0{n'^^''^) on the average, i. e.,

iJiA(0M«=O(n'+"*).

G. H. Hardy and S. Ramanujan^^^ employed the phrase "almost all
numbers have a specified property" to mean that the number of the num-
bers ^ X having this property is asymptotic to a: as a; increases indefinitely,
and proved that if / is a function of n which tends steadily to infinity with n,
then almost all numbers have between a — 6 and a-\-h different prime factors,
where a = log log n, h=f-\/d. The same result holds also for the total
number of prime factors, not necessarily distinct. Also a is the normal
order of the number of distinct prime factors of n or of the total number
of its prime factors, where the normal order of g{n) is defined to mean f{n)
if , for every positive e, (1— €)/(n)<gr(n)<(l+e)/(n) for almost all values
of n.

S. Wigert^^^ gave an asymptotic representation for l!,n^j:r{n){x — n)^.

E. T. BelP^ gave results bearing on this chapter.

F. RogeP^^ expressed the sum of the rth powers of the divisors ^g* of
m as an infinite series involving Bernoullian functions.

A. Cunningham^^^ found the primes p< lO'* (or 10^) for which the number
of divisors of p — 1 is a maximum 64 (or 120).

Hammond^^ of Ch. XI and RogeP^^ of Ch. XVIII gave formulas involv-
ing (J and r. Bougaief^^' ^^ of Ch. XIX treated the number of divisors
^ m of n. Gegenbauer^° of Ch. XIX treated the sum of the pth powers of
the divisors ^ m of n.

i^oProc. London Math. Soc, (2), 15, 1916, 1-25.

i"/&id., 192-213.

i82Quar. Jour. Math., 48, 1917, 76-92.

i83Acta Math., 41, 1917, 197-218.

is^Annals of Math., 19, 1918, 210-6.

i85Math. Quest. Educ. Times, 72, 1900, 125-6.

i86Math. Quest, and Solutions, 3, 1917, 65.

I

CHAPTER XL

MISCELLANEOUS THEOREMS ON DIVISIBILITY, GREATEST
COMMON DIVISOR. LEAST COMMON MULTIPLE.

Theorems on Divisibility.

An anonymous author^ noted that for n a prime the sum of 1 , 2, . . . , n — 1
taken by twos (as 1+2, 1+3,. . .), by fours, by sixes, etc., when divided
by n give equally often the residues 1, 2,..., n — 1, and once oftener the
residue 0. The sum by threes, fives, . . . , give equally often the residues
1,. . ., n — 1 and once fewer the residue 0.

J. Dienger^ noted that if w''-+'±l and (m^'-+2_ 1)7(^2 _i) are divisible
by the prime p, then the sum of any 2r+l consecutive terms of the set
1, m^", m^'^", m^'^", . . . is divisible by p. The case m = 2, r = l, p = 3 or 7
was noted by Stifel (Arith. Integra).

G. L. Dirichlet^ proved that when n is divided by 1, 2, . . ., n in turn
the number of cases in which the remainder is less than half the divisor
bears to n a ratio which, as n increases, has the limit 2 — log 4 = 0.6137
. . . ; the sum of the quotients of the n remainders by the corresponding
divisors bears to n a ratio with the limit 0.423 ....

Dirichlet^ generalized his preceding result. The number h of those
divisors 1,2,. . . , p (p^ ti), which yield a remainder whose ratio to the divisor
is less than a given proper fraction a, is

-liH-B-"]}

Assuming that pVn increases indefinitely with n, the limit of /i/p is a
if n/p increases indefinitely with n, but if n/p remains finite is

J. J. Sylvester^ noted that 2"""^^ is a factor of the integral part of /c^"*"*"^
and of the integer just exceeding h^"^, where ^ = l + \/3-

N. V. Bougaief^ called a number primitive if divisible by no square >1,
secondary if divisible by no cube. The number of primitive numbers ^ n is

H,{n)=i:q{u)+iq{u)+.. ., <i = [VnA'],

1 1 '

where q{u) is zero if u is not primitive, but is +1 or —1 for a primitive u,
according as ?/ is a product of an even or odd number of prime factors.

iJour. fiir Math., 6, 1830, 100-4. ^Archiv Math. Phys., 12, 1849, 425-9.

3Abh. Ak. Wiss. BerMn, 1849, 75-6; Werke, 2, 57-58. Cf. Sylvester, Amer. Jour. Math., 5,

1882, 298-303; CoU. Math. Papers, IV, 49-54.
<Jour. fur. Math., 47, 1854, 151-4. Berlin Berichte, 1851, 20-25; Werke, 2, 97'-104; French

transl. by O. Terquem, Nouv. Ann. Math., 13, 1854, 396.
^uar. Joum. Math., 1, 1857, 185. Lady's and Gentleman's Diary, London, 1857, 60-1.
"Comptes Rendus Paris, 74, 1872, 449-450. BuU. Sc. Math. Astr., 10, I, 1876, 24. Math.

Sbornik (Math. Soc. Moscow), 6, 1872-3, I, 317-9, 323-331.

327

328 History of the Theory of Numbers. [Chap, xi

To obtain the number Hoin) of secondary numbers ^n, replace square roots
by cube roots in the /,. We have

ffi(n)+Hi([|:,])+/fi([|]) + . . . =n, H2{n)+Ho{]^^ + . . . =n,

and similarly for Hi,_i{n) given by (2) below.

J. Grolous" considered the probability R^ that a number be divisible
by at least one of the integers Qi,. . ., Qk, relatively prime by twos, and
showed that

Chr. Zeller''" modified Dirichlet's^ expression for h. The sums

,=iLs J ,=iLs + aJ

are equal. The sum of the terms of the second with s>fjL = [\/p] equals
the excess of the sum of the first n terms of the first over fx^ or ju^ — 1 , the
latter in the case of numbers between fi^ and m^+m- Hence we may abbre-
\iate the computation of h.

E. Cesaro^ obtained Dirichlet's^'^ results and similar ones. The mean
(p. 174) of the number of decompositions of A^ into two factors having p as
their g. c. d. is 6(log N)/(p~Tr^). The mean (p. 230) of the number of
di\isors common to two positive integers n, n' is 7rV6, that of the sum of
their common di\isors is

ilog, nn'+2C-Y^+i,

where C = 0.57721 .... The sum of the inverses of the nth powers of two posi-
tive integers is in mean ^^+2) where s" is defined by (12) of Ch. X.

E. Cesaro^ proved the preceding results on mean values; showed that
the number of couples of integers whose 1. c. m. is n is the number of divisors
of n", if (a, b) and (6, a) are both counted when a^^b; found the mean of
the 1. c. m. of two numbers; found the probability that in a random division
the quotient is odd, and the mean of the first or last digit of the quotient;
the probability that the g. c.d. of several numbers shall have specified
properties.

Cesaro^" noted that the probability that an integer has no divisor > 1
which is an exact rth power is l/f(r).

L. Gegenbauer^° proved that the number of integers ^ x and divisible
by no square is asymptotic to Gx/tt", with an error of order inferior to
\/x- He proved the final formulas of Bougaief.^

'Bull. Sc. Soc. Philomatique de Paris, 1872, 11(>-128.
'"Nachrichten Gesell. Wiss. Gottingen, 1879, 265-8.

8M6m. Soc. R. Sc. de Li^ge, (2), 10, 1883, No. 6, 175-191, 219-220 (corrections, p. 343).
•Annali di mat., (2), 13, 1885, 235-351, "Excursions arith. 4 I'lnfini."
•"Nouv. Ann. Math., (3), 4, 1885, 421.

I'Denkschr. Akad. Wien (Math.), 49, 1, 1885, 47-8. Sitzungsber. Akad. Wien, 112, II a, 1903,
562; 115, II a, 1906, 589. Cf. A. Berger, Nova Acta Soc. Upsal., (3), 14, 1891, M6m. 2,
p. 110; E. Landau, Bull. Soc. Math. France, 33, 1905, 241. See Gegenbauer,".'" Ch. X.

Chap. XI] MISCELLANEOUS THEOREMS ON DIVISIBILITY. 329

Gegenbauer^°" proved that the arithmetical mean of the greatest integers
contained in k times the remainders on the division of n by 1, 2, . . ., n
approaches

k—l

k\ogk-{-k-l-ki:i/x

as n increases. The case A; = 2 is due to Dirichlet.

Gegenbauer^^ gave formulas involving the greatest divisor t^n), not
divisible by a, of the integer n. In particular, he gave the mean value of
the greatest divisor not divisible by an ath power.

L. Gegenbauer,^^ employing Merten's function ix (Ch. XIX) and
R{a)=a — \a\, gave the three general formulas

2 sV(^V(2/) = sV(A;) - i: m - i m,
Xi j/=i \y / k=i A=i it=i

where X2 ranges over the divisors >n of (r — l)n+l, (r — l)n+2, . . ., rn,
while Xi ranges over all positive integers for which

r-\-n ~ g r n \ ' g' ' ' gj

where g is the g. c. d. of r, n. Take f{x) = 1 or 0 according as x is an sth
power or not. Then the functions

(1) 2 /(A;), 2/x(^)/(2/)

k = \ y = \ \y/

become [-^m] and \{^), with the value 0 if the exponent of any prime
factor of X is ^0, 1 (mod s), otherwise the value ( — 1)", where a is the
number of primes occurring in x to the power /cs+1. Thus

2x,(x2) = \y^ - \</V^r?^ - [i/i\ •

If j{x) = 0 or 1 according as x is divisible by an sth power or not, the func-
tions (1) become Qs(w) and ix{\/x)j the former being the number of integers
^ m divisible by no sth power. If J{x) = 1 or 0 according as x is prime or
not, the functions (1) become the number of primes ^m and a simple func-
tion a(x) ; then the third formula shows that the mean density of the primes

loiDenkschr. Akad. Wien (Math.), 49, II, 1885, 108.
"Sitzungsber. Akad. Wiss. Wien (Math.), 94, 1886, II, 714.
i276id., 97, 1888, Ila, 420-6.

330 History of the Theory of Numbers. [Chap, xi

If /(x)=log X, the second function (1) becomes v{x), ha\ing the value*
log p when x is a power of the prime p, otherwise the value 0. Besides the
resulting formulas, others are found by taking J{x) = v{x), Jacobi's symbol
(A/x) in the theor>' of quadratic residues, and finally the number of repre-
sentations of X by the system of quadratic forms of discriminant A.

L. Saint-Loup^^ represented graphically the divisors of a number.
Write the first 300 odd numbers in a horizontal line; the 300 following
numbers are represented by points above the first, etc. Take any prime as
17 and mark all its multiples; we get a rectilinear distribution of these mul-
tiples, which are at the points of intersection of two sets of parallel lines.

J. Hacks^^ proved that the number of integers ^m which are divisible
by an nth power >1 is

p„(m) =S g„] -2 [^„] +S [jtTi^.] - . . . ,

where the A;'s range over the primes >1 [Bougaief^]. Then yp2{fn) =
m—p2{'m) is the number of integers ^m not divisible by a square >1, and

^.w+^.(f)+^.(f)+...+^.([-^.) =

m.

A like formula holds for \p3 = 7n — p3(m), using quotients of m by cubes.

L. Gegenbauer"" found the mean of the sum of the reciprocals of the
A:th powers of those divisors of a term of an unlimited arithmetical progres-
sion which are rth powers ; also the probabiUty that a term be divisible by no
rth power; and many such results.

L. Gegenbauer^^ noted that the number of integers 1, . . . , n not divisible
by a Xth power is

(2) Qx(n)= S^[5J/x(x).

Ch. de la Valine Poussin^® proved that, if x is divided by each positive
number ky-\-b^x, the mean of the fractional parts of the quotients has for
x= 00 the limit 1 — C; if x is divided by the primes ^x, the mean of the
fractional parts of the quotients has for x = co the limit 1 — C. Here C is
Euler's constant.^

L. Gegenbauer^^ proved, concerning Dirichlet's^ quotients Q of the
remainders (found on di\'iding n by 1 , 2, . . . , n in turn) by the corresponding
divisors, that the number of Q's between 0 and 1/3 exceeds the number of
Q's between 2/3 and 1 by approximately 0.179n, and similar theorems.

♦Cf. Bougaief 1" of Ch. XIX.

"Comptes Rendus Paris, 107. 1888, 24; ficole Norm. Sup., 7, 1890, 89.

"Acta Math., 14, 1890-1, 329-336.

""Sitzungsber. Ak. Wien (Math.), 100, Ila, 1891, 1018-1053.

^Ibid., 100, 1891, Ila, 1054. Denkschr. Akad. Wien (Math.), 49 I, II, 1885; 50 I, 1885. Cf.

Gegenbauer" of Ch. X.
"Annale.^ de la soc. ac. Bruxellea, 22, 1898, 84-90.
"Sitzungsberichte Ak. Wiaa. Wien (Math.), 110, 1901, Ila, 148-161.

Chap. XI] MISCELLANEOUS ThEOEEMS ON DIVISIBILITY. 331

He investigated the related problem of Dirichlet.* Finally, he used as
divisors all the sth powers ^ n and found the ratio of the number of remain-
ders less than half of the corresponding divisors to the number of the others.

L. E. Dickson^^" and H. S. Vandiver proved that 2">2(7i+l)(n' + l) . . .,
if 1, n, n', . • • are the divisors of an odd number n> 3.

R. Birkeland^^ considered the sum Sg of the qth. powers of the roots
Oi, . . ., flm of z'^+Aiz"'~^-\- . . . +^m = 0. If Si, . . . , s^ are divisible by the
power a^ of a prime a, then A^ is divisible by a" unless q is divisible by
a. If g is divisible by a, and a^' is the highest power of a dividing q, then
Afi is divisible by a^~^\ Then (n+aai) . . . (n+aa^) —n"" is divisible by a^.
In particular, the product of m consecutive odd integers is of the form
1+2^^ if m is divisible by 2".

E. Landau^^ reproduced Poussin's^^ proof of the final theorem and added
a simplification. He then proved a theorem which includes as special cases
the two of Poussin and the final one by Dirichlet^. Given an infinite class
of positive numbers q without a finite limit point and such that the number
of g's ^a; is asymptotic to x/w{x), where w{x) is a non-decreasing posi-
tive function having

x=oo w{x)

then if x is divided by all the q's ^ x, the mean of the fractional parts of the
quotients has for x = «> the limit 1 — C.

St. GuzeP° wrote 5(n) for the greatest odd divisor of n and proved in
an elementary way the asymptotic formulas

[X] rfi \X\ U^\

S 5(n) =|-+0(x), S ^^ =f:r+0(l),

n=l O n=l n

for 0 as in Pfeiffer^", Ch. X.

A. Axer^^ considered the x'''''(^) decompositions of n into such a pair
of factors that always the first factor is not divisible by a Xth power and
the second factor not by a z^th power, X^2, v'^2. Then S^iix'"'" (n) is
given asymptotically by a compHcated formula involving the zeta function.

F. RogeP^ wrote Rx,n for the algebraic sum of the partial remainders
<— [i] in (2), with n replaced by 2, and obtained

Qx(2)=2P,,„-|-i2x.n, Px.n= n (l-:;^x)'

where p„ is the nth prime and Pn''^ 2<p„+i. He gave relations between the
values of Qx{z) for various 2's and treated sums of such values, and tabu-
lated the values of ^2(2) and jB2,n for 2^288. He^^" gave many relations

I'^Amer. Math. Monthly, 10, 1903, 272; 11, 1904, 38-9.

"Archiv Math, og Natur., Kristiania, 26, 1904, No. 10.

"Bull. Acad. Roy. Belgique, 1911, 443-472.

"Wiadomoaci mat., Warsaw, 14, 1910, 171-180.

"Prace mat. fiz., 22, 1911, 73-99 (Polish), 99-102 (German). Review in Bull, des sc. math.,

(2), 38, II, 1914, 11-13.
^Sitzungsber. Ak. Wiss. Wien (Math.), 121, Ila, 1912, 2419-52.
"«/6id., 122, Ila, 1913, 669-700. See RogeP« of Ch. XVIII.

332 History of the Theory of Numbers. [Chap, xi

between the QAz), relations involving the number A{z) of primes ^z, and
relations involving both Q's and A's.

A. Rothe'*^^ called b a maximal divisor of a if no larger divisor of a con-
tains 6 as a factor. Then a/b is called the index of b with respect to a. 1|
If also c is a maximal divisor of b, etc., a,b, c, . . ., I are said to form a series
of composition of a. In all series of composition of a, the sets of indices
are the same apart from order [a corollary of Jordan's theorem on finite
groups applied to the case of a cyclic group of order a].

*Weitbrecht-^ noted tricks on the divisibility of numbers.

*E. Moschietti-^ discussed the product of the divisors of a number.

Each-^ of the consecutive numbers 242, 243, 244, 245 has a square factor
> 1 ; likewise for the sets of three consecutive numbers beginning with 48
or 98 or 124.

C. Avery and N. Verson^^ noted that the consecutive numbers 1375,
1376, 1377 are divisible by 5^ 2\ 3^ respectively.

J. G. van derCorput^^ evaluated the sum of thenth powersof all integers,
not divisible by a square >1, which are ^x and are formed of r prime
factors of m.

Greatest Common Divisor, Least Common Multiple.

On the number of divisions in finding the g. c. d. of two integers, see
Lame^^ et seq. in Ch. XVII; also Binet^^ and Dupre^.

V.A.Lebesgue^^notedthatthel.c.m.of a, . . .,A;is(p]P3P5. . ■)/{v2ViP&- ■ ■)
if pi is the product of a, ... , k, while p2 is the product of their g. c. d.'s two
at a time, and ps the product of their g. c. d.'s three at a time, etc. If a, 6, c
have no common divisor, there exist an infinitude of numbers ax-^b rela-
tively prime to c.

V. Bouniakowsky^^ determined the g. c. d. N of all integers represented
by a polynomial /(x) with integral coefficients without a common factor.
Since A^ divides the constant term of f{x), it remains to find the highest
power p" of a prime p which divides J{x) identically, i. e., for x = 1, 2, . . . , p".
Divide /(x) by Xp={x — 1). . .{x — p) and call the quotient Q and remain-
der R. Then must R^O (mod p") for x = l,. . ., p, so that each coefficient
of R is divisible by p", and iu = Mu vvhere p"' is the highest power of p divid-
ing the coefficients of i?. If /ii = l, wehaveju= 1. Next, let /ii>l. Divide

^^Zeitschrift Math.-Xaturw. Unterricht, 44, 1913, 317-320.

"Vom Zahlenkunststiick zur Zahlentheorie, Korrcspondenz-Blatt d. Schulen Wiirttembergs,

Stuttgart, 20, 1913, 200-6.
"Suppl. al Periodico di Mat., 17, 1914, 115-6.
i^Math. Quest. Educ. Times, 36, 1881, 48.
2'Math. Miscellany, Flushing, N. Y., 1, 1836, 370-1.
"Nieuw Archief voor Wi.skunde, (2), 12, 1918, 213-27.
"Jour, de Math., (1), 6, 1841, 453.
»Ibid., (1), 11, 1846, 41.
'*Nouv. Ann. Math., 8, 1849, 350; Introduction k la th6orie des nombres, 1862, 51-53; Exercises

d'analyse num^rique, 1859, 31-32, 118-9.
"M<5m. acad. sc. St. P^tersbourg, (6), ac. math, et phys. 6 (so. math. phys. et nat. 8), 1857

305-329 (read 1854); extract in Bulletin. 13, 149.

Chap. XI] GREATEST COMMON DiVISOR. 333

Q by (x — p — l)... {x — 2p) and call the quotient Q' and remainder R'.
Then must X^R'+XopQ'^O and hence XpR'=0 (mod p"). Thus if 1^2 is
the exponent of the highest power of p dividing the coefficients of R', we
have At^M2 + l- In general, if [j.^ and X^-i are the exponents of the highest
powers of p dividing the coefficients of the remainder i?'^~^^ and X^k-Dp
identically, then fi^ iJLk+\k-i' Finally, if l = [m/p], /x^X^. The extension
to several variables is said to present difficulties. [For simpler methods,
see Hensel^^ and Borel.^^] It is noted (p. 323) that

are identically divisible by p". It is conjectured (p. 328) that/(a;)/iV repre-
sents an infinitude of primes when f{x) is irreducible.

E. Cesaro" and J. J. Sylvester^^ proved that the probabihty that two
numbers taken at random from 1 , . . . , n be relatively prime is Q/tt^ asymp-
totically.

L. Gegenbauer^^ gave 16 sums involving the g. c. d. of several integers
and deduced 37 asymptotic theorems such as the fact that the square of
the g. c. d. of four integers has the mean value IS/tt^. He gave the mean
of the kth. power of the g. c. d. of r integers.

J. Neuberg^^" noted that, if two numbers be selected at random from
1, . . .,N, the probability that their sum is prime to N is k=cf){N) 0Tk/{N—l)
according as N is odd or even.

T. J. Stieltjes,^^ starting with a set of n integers, replaced two of them
by their g. c. d. and 1. c. m., repeated the same operation on the new set,
etc. Finally, we get a set such that one number of every pair divides the
other. Such a reduced set is unique. The 1. c. m. of a, . . . , ? can be
expressed (pp. 14-16) as a product a'. . J' of relatively prime factors divi-
ding a,...,l, respectively. The 1. c. m. (or g. c. d.) oi a,h,. . .,1 equals the
quotient oi P = ab. . .Ihy the g. c. d. (or 1. c. m.) of P/a, P/b, . . . , P/l.

E. Lucas^^ gave theorems on g. c. d. and 1. c. m.

L. Gegenbauer^^" considered in connection with the theory of primes,
the g. c. d. of r numbers with specified properties.

J. Hacks^^ expressed the g. c. d. of m and n in the forms

ql^]-.n^.^n, 2'|;[f]+2'}:g]-2[|][|]-^.

where € = 0 or 1 according as m, n are both or not both even.

J. Hammond^^ considered arbitrary functions / and F oi p and a, such

"Mathesis, 1, 1881, 184; Johns Hopkins Univ. Circ, 2, 1882-3, 85.

"Johns Hopkins Univ. Circ, 2, 1883, 45; Comptes Rendus Paris, 96, 1883, 409; Coll. Papers, 3,

675; 4, 86.
"Sitzungsberichte Ak. Wiss. Wien (Math.) 92, 1885, II, 1290-1306.
39«Math. Quest. Educ. Times, 50, 1889, 113-4.

^''Sur la theorie des nombres, Annales de la fac. des sciences de Toulouse, 4, 1890, final paper.
^iTheorie des nombres, 1891, 345-6; 369, exs. 4, 5.
""Monatshefte Math. Phys., 3, 1892, 319-335.
*2Acta Math., 17, 1893, 208.
^Messenger Math. 24 1894^5 17-19.

334 History of the Theory of Numbers. [Chap, xi

that /(p, 0) = 1 , F{p, 0)=0, and any two integers m=np", n='n.p^, where
the p's are distinct primes and, for any p, a ^ 0, /3 ^ 0. Set

rP{7n)=Uf{p,a), $=2F(p, a).

By the usual proof that mn equals the product of the g. c. d. M of m and n
by their 1. c. m. n, we get

yPim)4/{n)=^P{M)xl/(jx), <I>(w)+$(n) =$(M)+$(iu).

In particular, if m and n are relatively prime,

yl/{m)\p{n) =\p{vin), $(w)+<l>(n) =<l>(mn).

These hold if i/' is Euler's 0-function, the sum o-(m) of the divisors of
m or the number T{m) of divisors of ?n ; also, if ^{m) is the number of prime
factors of vi or the sum of the exponents a in m = Iip''.

K. Hensel^ proved that the g. c. d. of all numbers represented by a
polynomial F{u) of degree n with integral coefficients equals the g. c. d. of
the values of F{u) for any n+1 consecutive arguments. For a polynomial
of degree ni in Ui, 712 in ^2, • ■ • we have only to use ni + 1 consecutive
values of ui, 712+ 1 consecutive values of U2, etc.

F. Klein"*^ discussed geometrically Euclid's g. c. d. process.

F. ^Vlertens^^ calls a set of numbers primitive if their g. c. d. is unity.
If 7719^0, k>\, and ai,. . ., o^, m is a primitive set, we can find integers
Xi,. . ., Xk so that ai-\-mxx,. . ., ak+mxk is a primitive set. Let d be the
g. c. d. of fli, . . ., Oi- and find 5, ji so that db-\-vi^ = \. Take integral solu-
tions a of OittiH-. . .+akak = d and primitive solutions ^i not all zero of
aij3i+ . . . +aii3/; = 0. Then 7i=/3,+6a,('i = l,. . ., k) is a primitive set.
Determine integers ^ so that 71^1+. . .+7*^^ = 1 and set a:,=/i^<. Then
Ci+TTix, form a primitive set.

R. Dedekind^^ employed the g. c. d. d oi a,h, c; the g. c. d. (6, c) =Oi,
(c, a) = 61, (a, h) = Ci. Then a' = ajd, h' = hi/d, c' = C]/d are relatively prime
in pairs. Then cf6'c' is the 1. c. m. of 61, Ci, and hence is a divisor of a. Thus
a = dh'c'a", h = dc'a'b", c = da'h'c". The 7 numbers a', . . .,a" ,. . .,d are called
the " Kerne" of a, h, c. The generalization from 3 to n numbers is given.

E. Borel'*^ considered the highest power of a prime p which di\'ides a
polynomial P{x, y,. . .) with integral coefficients for all integral values of
X, y,. . .. If each exponent is less than p, we have only to find the highest
power of p dividing all the coefficients. In the contrary case, reduce all
exponents below p by use of x^ = x-\-pxi,Xi' = Xi -\-px2,. . . and proceed as
above with the new polynomial in x, Xi, X2,...,y,yi,.... Then to find all
arithmetical divisors of a polynomial P, take as p in turn each prime less
than the highest exponent appearing in P.

L. Kronecker^^ found the number of pairs of integers i, k having t as
their g. c. d., where l^i^m, l^k^n. The quotient of this number by

«Jour. fur Math., 116, 1896, 350-6.

"Ausgewahlte Kapitel der Zahlentheorie, I, 1896.

*«Sitzung8berichte Ak. Wiss. Wien (Math.), 106, 1897, II a, 132-3.

*^Ueber Zerlegungen von Zahlen durch d. grossten gemeinsamen Teller, Braunschweig, 1897.

"BuU. Sc. Math. Astr., (2), 24 I, 1900, 75-80. Cf. Borel and Drach'^ of Ch. III.

"Vorlesungen uber Zahlentheorie, I, 1901, 306-312.

i

Chap. XI] GREATEST COMMON DiVISOR. 335

mn is the mean. When m and n increase indefinitely, the mean becomes
Q/iirH"^). The case ^=1 gives the probability that two arbitrarily chosen
integers are relatively prime; the proof in Dirichlet's Zahlentheorie fails to
establish the existence of the probability.

E. DintzP° proved that the g. c. d. A(a, . . ., e) is a linear function of
a, . . . , e, and reproduced the proof of Lebesgue's^^ formula as given in
Merten's Vorlesungen iiber Zahlentheorie and by de Jough.^^

A. Pichler,^°" given the 1. c. m. or g. c. d. of two numbers and one of them,
found values of the other number.

J. C. Kluyver^^ constructed several functions z (involving infinite series
or definite integrals) which for positive integral values of the two real
variables equals their g. c. d. He gave to Stern's^^ function the somewhat
different form [;r] / \

W. Sierpinski^^ stated that the probability that two integers ^n are
relatively prime is . „ p -,2

contrary to Bachmann, Analyt. Zahlentheorie, 1894, 430.
G. Darbi^^ noted that if a = (a, N) is the g. c. d. of a, N,

(iV,abc...)=a(6,^)(c,^(^_^/J

and gave a method of finding the g. c. d. and 1. c. m. of rational fractions
without bringing them to a common denominator.

E. Gelin^® noted that the product of n numbers equals ah, where a is
the 1. c. m. of their products r at a time, and h is the g. c. d of their products
n — r at a time.

B. F. Yanney^'^ considered the greatest common divisors Di, D2, ... of
tti, . . . , a„ in sets of k, and their 1. c. m.'s Li, L2, . . . . Then

HA Lt' ^ (ai . . . «n)^ ^ n D ^-^L„ 5 = (^y c = (^~ I) .

The limits coincide ii k = 2. The products have a single term iik = n.

P. Bachmann^^ showed how to find the number N obtained by ridding
a given number n of its multiple prime factors. Let d be the g. c. d. of n
and 0(n). If d = n/d occurs to the rth power, but not to the (r+l)th power
in n, set ni = n/5^ From rii build di as before, etc. Then N = 86182 ....

"Zeitschrift fiir das Realschulwesen, Wien, 27. 1902, 654-9, 722.

6o«76id., 26, 1901, 331-8.

"Nieuw Archief voor Wiskunde, (2), 5, 1901, 262-7.

^^K. Ak. Wetenschappen Amsterdam, Proceedings of the Section of Sciences, 5, II 1903, 658-

662. (Versl. Ak. Wet., 11, 1903, 782-6.)
"Jour, flir Math., 102, 1888, 9-19.
"Wiadomosci Mat., Warsaw, 11, 1907, 77-80.
^^Giornale di Mat., 46, 1908, 20-30.
S6I1 Pitagora, Palermo, 16, 1909-10, 26-27.
"Amer. Math. Monthly, 19, 1912, 4-6.
6«Archiv Math. Phys., (3), 19, 1912, 283-5.

336

History of the Theory of Numbers.

[Chap. XI

Erroneous remarks^^ have been made on the g. c. d. of 2"" — 1, 3"" — 1.

]\I. Lecat^° noted that, if a,j is the 1. c. m. of i and j, the determinant
loyl was evaluated by L. Gegenbauer,^^ who, however, used a law of multi-
pHcation of determinants valid only when the factors are both of odd class.

J. Barinaga®^" proved that, if 5 is prime to iV = nk, the sum of those terms
of the progression A'', N-\-d, iV+25, . . . , which are between nk and n{k-\-hd)
and which have with n = mp the g. c. d. p, is ^n<l){n/p){2k-\-hd)h.

R. P. Willaert®- noted that, if P{n) is a polynomial in n of degree p with
integral coefficients, f{n)=aA'"'-\-P{n) is divisible by D for every integral
value of 7} if and only if the difference A''f{0) of the Ath order is di\"isible
by D for k = 0, 1,. . ., p-\-l. Thus, if p = l, the conditions are that /(O),
/(l),/(2) be divisible by D.

*H. Verhagen^^ gave theorems on the g. c. d. and 1. c. m.

H. H. ]\Iitchell^ determined the number of pairs of residues a, b modulo X
whose g. c. d. is prime to X, such that ka, kb is regarded as the same pair as
a, b when k is prime to X, and such that X and ax + by have a given g. c. d.

W. A. Wijthoff^^ compared the values of the sums

S (-l)'"-WF{(w, a)}, "s m'F{{m,a)}, s = l, 2,

m=l m=l

where {m, a) is the g. c. d. of m, a, while F is any arithmetical function.

F. G. W. Brown and C. M. Ross^^ wTote h, U, ...,ln for the 1. c. m
the pau-s Ai, A^; A^, Az; . . . ; A„, Ai, and gi, g^, ■ ■ ., gn for the g
these pairs, respectively. If L, G are the 1. c, m. and g. c. d. of Ai,
A„, then

gm . . .gn = G'',

. c

^2,

of
d. of

9i92

C. de Polignac^^ obtained for the g. c. d

(a\btJi)={a,by{\,fx).(--\

\{a, b) (X, m)

Sylvester^* and others considered the g. c. d

9n G'

(a, 6) of a, 6 results like
fi \ / b X

J \(a, 6)' (X, mV

6)' (X, m)>

of Z)„ and Z)„+i where D^
is the n-rowed determinant whose diagonal elements are 1, 3, 5, 7, . . .,
and having 1, 2, 3, 4, ... in the line parallel to that diagonal and just above
it, and units in the parallel just below it, and zeros elsewhere.

On the g. c. d., see papers 33-88, 215-6, 223 of Ch. V, Cesaro" of Ch.
X, Cesaro^' ' of Ch. XI, and Kronecker^^ of Ch. XIX.

"L'interm6diaire des math., 20, 1913, 112, 183-4, 228; 21, 1914, 36-7.

^''Ibid., 21, 1914, 91-2.

•'Sitzungs. Ak. Wiss. Wien (Math.), 101, 1892, II a, 425-494.

""Annaes Sc. Acad. Polyt. do Porto, 8, 1913, 248-253.

^Mathesis, (4), 4, 1914, 57.

"Nieuw Tijdschria voor Wiskunde, 2, 1915, 143-9.

"Annals of Math., (2), 18, 1917, 121-5.

"Wiskundige Opgaven, 12, 1917, 249-251.

"Math. Quest, and Solutions, 5, 1918, 17-18.

«'Xouv. Corresp. Math., 4, 1878, 181-3.

6»Math. Que.st. Educ. Times, 36, 1881, 97-8; correction, 117-8.

CHAPTER XII.

CRITERIA FOR DIVISIBILITY BY A GIVEN NUMBER.

In the Talmud^ lOOa+6 is stated to be divisible by 7 if 2a+b is divis-
ible by 7.

Hippolytos^", in the third century, examined the remainder on the
division of certain sums of digits by 7 or 9, but made no appHcation to
checking numerical computation.

Avicenna or Ibn Sina (980-1037) is said to have been the discoverer
of the familiar rule for casting out of nines (cf . Fontes^^) ; but it seems to
have been of Indian origin.-^''

Alkarkhi^^ (about 1015) tested by 9 and 11.

Ibn Musa Alchwarizmi^'* (first quarter of the ninth century) tested by 9.

Leonardo Pisano^^ gave in his Liber Abbaci, 1202, a proof of the' test
for 9, and indicated tests for 7, 11.

Ibn Albanna^-'^ (born about 1252), an Arab, gave tests for 7, 8, 9.

In the fifteenth century, the Arab Sibt el-Maridini^'' tested addition by
casting out multiples of 7 or 8.

Nicolas Chuquet^^ in 1484 checked the four operations by casting out 9's.

J. Widmann^'' tested by 7 and 9.

Luca Paciuolo^ tested by 7, as well as by 9, the fundamental operations,
but gave no rule to calculate rapidly the remainder on division by 7.

Petrus Apianus^" tested by 6, 7, 8, 9.

Robert Recorde^'' tested by 9.

Pierre ForcadeP noted that to test by 7 = 10 — 3 we multiply the first
digit by 3, subtract multiples of 7, add the residue to the next digit, then
multiply the sum by 3, etc.

Blaise Pascal^ stated and proved a criterion for the divisibility of any
number N by any number A. Let ri, r2, 7*3, . . . , be the remainders obtained
when 10, lOfi, lOrg, ... are divided by A. Then iV = a+ 106 + 100c+ ... is
divisible by A if and only if a-\-rib-\-r2C+ . . . is divisible by A.

'Babylonian Talmud, Wilna edition by Romm, Book Aboda Sara, p. 96.

i«M. Cantor, Geschichte der Math., ed. 3, I, 1907, 461.

^^Ibid., 511, 611, 756-7, 763-6.

i^Cf. Carra de Vaux, Bibliotheca Math., (2), 13, 1899, 33-4.

i<^M. Cantor, Geschichte der Math., ed. 3, I, 1907, 717.

i^Scritti, 1, 1857, 8, 20, 39, 45; Cantor, Geschichte, 2, 1892, 8-10.

'/Le TaUfhys d'Ibn Albanna public et traduit par A. Marre, Atti Accad. Pont. Nuovi Lincei,

17, 1863-4, 297. Cf. M. Cantor, Geschichte Math., I, ed. 2, 757, 759; ed. 3, 805-8.
iffLe Triparty en la science de nombres. Bull. Bibl. St. Sc. Math., 13, 1880, 602-3.
^''Behede vnd hubsche Rechnung . . . , Leipzig, 1489.

^Summa de arithmetica geometria proportion! et proportionalita, Venice, 1494, f. 22, r.
2"Ein newe. . .Kauffmans Rechnung, Ingolstadt, 1527, etc.
^^The Grovnd of Artes, London, c. 1542, etc.
^L'Arithmeticqve de P. Forcadel de Beziers, Paris, 1556, 59-60.
*De numeris multiphcibus, presented to the Acad^mie Parisienne, in 1654, first published in

1665; Oeuvres de Pascal, 3, Paris, 1908, 311-339; 5, 1779, 123-134.

337

338 History of the Theory of Numbers. [Chap, xii

D'Alembert^ noted that if N = A-10'"+B-W-\-. ..+E is divisible by
10-6, then Ab"'+Bb"-\- . ..+E is divisible by 10-6; if A' is divisible by
10+6, then A(-6)'"+B(-6)"+ . . . +^ is divisible by 10+6. The case
6 = 1 gives the test for divisibiUty by 9 or 11. By separating A'' into parts
each with an even number of digits, N = A-10"'+ . . . +E, where m, . . .are
even; then if A^ is di\'isible by 100-6, Ah"*^^ -\- . . . + E is divisible by
100-6.

De Fontenelle^ gave a test for divisibility by 7 which is equivalent to
the case 6 = 3 of D'Alembert; to test 3976 multiply the first digit by 3 and
add to the second digit; it remains to test 1876. For proof see F. Sanvitali,
Hist. Literariae Italiae, vol. 6, and Castelvetri.^

G. W. Kraft^ gave the same test as Pascal for the factor 7.

J. A. A. Castelvetri^ gave the test for 99: Separate the digits in pairs,
add the two-digit components, and see if the sum is a multiple of 99. For
999 use triples of digits.

Castelvetri^ tested 1375, for example, for the factor 11 by noting that
13+75 = 88 is divisible by 11. If the resulting sum be composed of more
than two digits, pair them, add and repeat. To test for the factor 111,
separate the digits into triples and add. The proof follows from the fact
that lO-*" has the remainder 1 when divided by 11.

J. L. Lagrange^° modified the method of Pascal by using the least
residue modulo A (between — .4/2 andyl/2) in place of the positive residue.
He noted that if a number is written to any base a its remainder on division
by a — 1 is the same as for the sum of its digits.

J. D. Gergonne^^ noted that on di\dding iV = Ao+Ai6"*+A26^'"+ . . .,
written to base 6, by a di\'isor of 6'" — 1, the remainder is the same as on
dividing the sum A0+A1+A2+ ... of its sets of m digits. Similarly for
6'"+l and A0-A1+A2-A3+ • • ••

C. J. D. HilP^ gave rules for abbre\dating the testing for a prime factor
p, for p<300 and certain larger primes.

C. F. Liljevalch^^a ^^^^^ ^^^^^ jf lO^a-/? is di\^sible by p then a- 10^6
will be a multiple of p if and only if aa — /36 is a multiple of p.

J. ]\I. Argardh" used Hill's symbols, treating divisors 7, 17, 27, 1429.

F. D. Herter^^ noted that a + 106+100c+ ... is divisible by 10n±l if

'Manuscript R. 240* 6 (8°), Bibl. Inst. France, 21, ff. 316-330, Sur une propri^t^ des nombres.
•Histoire Acad. Paris, ann^e 1728, 51-3. 'Comm. Ac. Sc. Petrop, 7, ad annos 1734-5, p. 41.
»De Bononiensi Scientiarum et Artium Institute atque Academia Comm., 4, 1757; commen-

tarii, 113-139; opuscula, 242-260.
•De Bononiensi Scientiarum et Artium Institute atque Academia Comm., vol. 5, 1767, part 1,

pp. 134-144; part 2, 108-119.
"Lemons 6\6m. sur les math, donn^es k I'^cole normale en 1795, Jour, de I'^cole polytechnique,

vols. 7, 8, 1812, 194-9; OemTes, 7, pp. 203-8.
"Annales de math, (ed., Gergonne), 5, 1814-5, 170-2.
"Jour, fur Math., 11, 1834, 251-261; 12, 1834, 355. Also, De factoribua numerorum com-

positonim dignoscendis, Lund, 1838.
"<»De factoribus numerorum compositorura dignoscendis, Lund, 1838.
"De residuis ex divisione. . ., Diss. Lund, 1839.
"Ueber die Kennzeichen der Theiler einer Zahl, Progr. Berlin, 1844.

Chap. XII] CRITERIA FOR DIVISIBILITY. 339

a=F&/nH-c/n^=F . . . is divisible by 10n±l, with a like test for 10n±3
(replacing 1/n by 3/n), and deduced the usual tests for 9, 11, 7, 13, etc.

A. L. Crelle^^ noted that to test XmA""-^ . . . +XiA-i-Xo for the divisor s
we may select any integer n prime to s, take r=nA (mod s), and test

for the divisor s. For example, if A = 10, s = 7, 10^=— 1 (mod 7), so that
Xo — Xi-\-X2—. . . ±0:^ is to be tested for the divisor 7, where Xq, . . .are the
three-digit components of the proposed number from right to left. Simi-
larly for s=9, 11, 13, 17, 19.

A. Transon^^ gave a test for the divisibility of a number by any divisor
of 10"-n±l.

A. Niegemann^^ noted that 354578385 is divisible by 7 since 35457 -f
2X8385 is divisible by 7. In general if the number formed by the last m
digits of A^ is multiplied by k, and the product is added to the number de-
rived from N by suppressing those digits, then N is divisible by d if the
resulting sum is divisible by d. Here k{0<k<d) is chosen so that 10'"/: — 1
is divisible by d. Thus k = 2 if m = 4, d = 7.

Many of the subsequent papers are listed at the end of the chapter.

H. Wilbraham^^ considered the exponent p to which 10 belongs modulo
m, where m is not divisible by 2 or 5. Then the decimal for 1/m has
a period of p digits. If any number N be marked off into periods of p-
digits each, beginning with units, so that A^ = ai + 10^a2+10^^a34- • • •,
then ai-\-a2-]- ■ ■ ■ = N (mod m), and N is divisible by m if and only if
«i+<J2+ • • ■ is divisible by m.

E. B. Elliott^^ let 10'' = MD+r^,. Thus iV = 10%-h . . . +10ni+no is
divisible by D if N ='ZfnjMD-{-'Znjrj is divisible by D. The values of the r's
are tabulated for D = S, 7, S, 9, 11, 13, 17.

A. Zbikowski^° noted that N = a-\-10kis divisible by 7 if k — 2a is divis-
ible by 7. If 8 is of the form lOn+1, N = a-\-10k is divisible by 5 if A; — na is
divisible by d ; this holds also if 5 is replaced by a divisor of a number 10n+ 1 .

V. ZeipeP^ tests for a divisor h by use of nh = 10d-\-l. Then 10a2+ai is
divisible by 6 if a2 — aid is divisible by b.

J. C. Dupain^^ noted, for use when division by p — 1 is easy, that
N={p — 1)Q+R is divisible by p if R — Q is divisible by p.

F. Folie^^ proved that if a, c are such that ak'^ck = mp then AB-\-C is
divisible by the prime p = aB-{-c if Ak'=^Ck = m'p, provided a, c, k, k' are

isjour. fur Math., 27, 1844, 125-136.

16N0UV. Ann. Math., 4, 1845, 173-4 (cf. 81-82 by O. R.).

i^Entwickelung u. Begrlindung neuer Gesetze iiber die Theilbarkeit der Zahlen. Jahresber.

Kath. Gym. Koln, 1847-8.
i^Cambridge and Dublin Math. Jour., 6, 1851, 32.
"The Math. Monthly (ed. Runkle), 1, 1859, 45-49.
"oBull. ac. sc. St. Petersbourg, (3), 3, 1861, 151-3; Melanges math. astr. ac. St. P^tersbourg,

3, 1859-66, 312.
2iOfversigt finska vetensk. forhandl., Stockhohn, 18, 1861, 425-432.
«Nouv. Ann. Math., (2), 6, 1867, 368-9.
23M6m. Soc. Sc. Liege, (2), 3, 1873, 85-96.

340 History of the Theory of Numbers. [Chap, xii

not multiples of p. Application is made to the primes p^37. Again, if
p is a prime and

aB-+cB+d = ak"-\-ck'-\-dk = Ak"-{-Ck'-\-Dk = mp,

where k, k', k" are prime to p, then AB~-\-CB-[-D is divisible by p provided
k'^ — kk" is a multiple of p.

C. F. IMoller and C. Holten-^ would test the divisibility of n by a given
prime p by seeking a such that ap= =*= 1 (mod 10) and subtracting from n
such a multiple of ap that the difference ends with zero.

L. L. Hommel"-^ made remarks on the preceding method.

V. SchlegeP^ noted that if the di\isor to be tested ends with 1, 3, 7 or 9,
its product by 1, 7, 3 or 9 is of the form (i = lOX+1. Then a, with the final
digit u, is divisible by d\i ai = {a — ud)/\0 is. Then treat Oj aswe did a, etc.

P. Otto"^ would test Z for a given prime factor p by seeking a number n
such that if the product by n of the number formed by the last s digits of Z
be subtracted from the number represented by the remaining digits, the
remainder is di\'isible by p if and only if Z is. ^Material is tabulated for the
application of the method when p<100.

N. V. Bougaief-^" noted that a^. . .Ci to base B is divisible by D if
fli . . .a„ to base d is divisible by D, where dB= 1 (mod D). For jB = 10 and
Z) = 10/1+9, 1, 3, 7, we may take c? = n + l, 9?i+l, 3nH-l, 7n+5, respec-
tively. Again, kB--\-aB-\'h is di\'isible by D if kB-\-a-\-hd is divisible.

W. Mantel and G. A. Oskamp'^ proved that, to test the di\isibility of a
number to any base by a prime, the value of the coefficient required to
eliminate one, two, . . . digits on subtraction is periodic. Also the number of
terms of the period equals the length of the period of the periodic fraction
arising on division by the same prime.

G. Dostor-^'' noted that \{)t-\-u is divisible by any divisor a of 10A± 1 if
t=^Au is di\dsible by a. [A case of Liljevalch^-''.]

Hocevar^^ noted that if N, wTitten to base a, is separated into groups
Gi, (x2, . . . each of q digits, N is di\'isible by a factor of a'+l if Gi — G2+G3
- ... is divisible. Thus, for a = 2, g = 4, A'' = 104533, or 11001100001010101
to base 2 is divisible by 17 since 0101-0101 + 1000-1001 + 1 = 0.

J. Delboeuf^° stated that if p, q are such that pa-\-qh is a multiple of Z) and
if N = Aa.-\-B^ is a multiple of Z) = aa + 6/3, then pA+qB is a multiple of Z).

E. Catalan {ibid., p. 508) stated and proved the preceding test in the
following form: If a, h and also a', h' are relatively prime, and

iV = aa'+66', Nx = Aa-\-Bh, Nx' = A'a'+B'h',

then AA'-\-BB' is a multiple of A^ (and a sum of 2 squares if N is).

"Tidsskrift for Math., (3^, 5, 1875, 177-180. «*Tidsskrift for Math., (3), 6, 1876, 15-19.

"Zeitschrift Math. Phys., 21, 1876, 365-6. »'Zeitschrift Math. Phys., 21, 1876, 366-370.

^"''Mat. Sbornik (Math. Soc. Moscow), 8, 1876, I, 501-5.

"Nieuw Archief voor Wiskunde. Amsterdam, 4, 1878, 57-9, 83-94.

"-^.Ajchiv Math. Phys., 63, 1879, 221-4.

"Zur Lehre von der Teilbarkeit. . ., Prog. Imisbruck, 1881.

"La Revue Scientifique de France, (3), 38, 1886, 377-8.

Chap. XII] CRITERIA FOR DIVISIBILITY. 341

Noel (ibid., 378-9) gave tests for divisors 11, 13, 17,. . ., 43.

Bougon {ibid., 508) gave several tests for the divisor 7. For example,
a number is divisible by 7 if the quadruple of the number of its tens dimin-
ished by the units digit is divisible by 7, as 1883 since 188-4 — 3 = 749 is
divisible by 7. J. Heilmann (ibid., 187) gave a test for the divisor 7.

P. Breton and Schobbens {ibid., 444-5) gave tests for the divisor 13.

S. Dickstein^^ gave a rule to reduce the question of the divisibility of a
number to any base by another to that for a smaller number.

A. Loir^2 gave a rule to test the divisibihty of N, having the units digit a,
by a prime P. From {N — a)/10, subtract the product of a by the number,
say (mP — 1)/10, of tens in such a multiple mP of P that the units digit is 1.
To the difference obtained apply the same operation, etc., until we exhaust
N. If the final difference be P or 0, N is divisible by P.

R. Tucker^^ started with a number N, say 5443, cut off the last digit 3
and defined ^2 = 544 — 2-3 = 538, ^3 = 53 — 2-8, etc. If any one of the ^^'s is
divisible by 7, N is divisible by 7. R. W. D. Christie (p. 247) extended the
test to the divisors 11, 13, 17, 37, the respective multiphers being 1, 9, 5, 11,
provided always the number tested ends with 1, 3, 7 or 9.

R. Perrin^^ would find the minimum residue of N modulo p as follows.
Decompose N, written to base x, into any series of digits, each with any
number of digits, say A, Bi, Cj,. . ., where Bi has i digits. Let p be any
integer prime to x and find qi so that qiX^^ 1 (mod p). Let a be any one of
the integers prime to p and numerically <p/2. Let j8 be the ith integer
following a in that one of the series containing a which are defined thus:
as the first series take the residues modulo p of 1, g, g^, . . . ; as the second
series take the products of the preceding residues by any new integer prime
to p; etc. Let y be the jth integer following /S in the same series, etc.
Then N' = Aa-\-BS-{-Cjy-\-... is or is not divisible by p according as
A'' is or not. By repetitions of the process, we get the minimum residue
of N modulo p. The special case A-{-Biqi, with p a prime, is due to Loir.^^

Dietrichkeit^^ would test Z = \Ok-\-a for the divisor n by testing k — xa,
where 10a:+l is some multiple of n. To test Z (pp. 316-7) for the divisor
7, test the sum of the products of the units digit, tens digit, ... by 1, 3, 2, 6,
4, 5, taken in cyclic order beginning with any term (the remainders on con-
verting 1/7 into a decimal fraction) . Similarly for 1/n, when n is prime to 10.

J. Pontes^ ^ would test N for a divisor M by using a number <iV and
= N (mod M), found as follows. For the base B, let q be the absolutely
least residue of B"" modulo M. Commencing at the right, decompose N
into sets of m digits, as X,„, . . . , a^, and set f{x)=a^x"'+^jn^"'~^-\- . . . +X;;,,
whence N=f{B'^). By expanding N=f{q+M^), we see that f{q) is the
desired number < N and = N (mod M) .

S. Levanen^^ gave a table showing the exponent to which 10 belongs for

siLemberg Museum (Polish), 1886. "Comptes Rendus Paris, 106, 1888, 1070-1; errata, 1194.
^'Nature, 40, 1889, 115-6. 34 Assoc, franp. avanc. sc, 18, 1889, II, 24-38.

'^Zeitschr. Math. Phys., 36, 1891, 64. 3«Comptes Rendus Paris, 115, 1892, 1259-61.
"Ofversigt af finska vetenskaps-soc. forhandUngar, 34, 1892, 109-162. Cf . Jahrbuch Fortschr.
Math., 24, 1892, 164-5.

342 History of the Theory of Numbers. [Chap, xii

primes 6<200 and certain larger primes, from which are easily deduced
tests for the divisor 6.

Several"" noted that if 10 belongs to the exponent n modulo d, and if
Si, Si, ■ ■ .denote the sums of every nth digit of N beginning with the first,
second, ... at the right, the remainder on the division of A^ by d is that of
S1 + IOS2+IO-S3+ . . .

J. Fontes^^ would find the least residue of A^ modulo M. If 10" has the
residue q modulo M, we do not change the least residue of N if we multiply
a set of n digits of A^ by the same power of q as of 10". Thus for M = 19,
iV=10433 = 10'+4-10H33, 10" has the residue 5 modulo 19 and we may
replace N by 5- +4 ',5+ 33. The method is applied to each prime M^ 149.

Fontes^^ gave a history of the tests for divisibility, and an "extension
of the method of Pascal," similar to that in his preceding paper.

P. Valerio*° would test the divisibility of N by 39, for example, by sub-
tracting from N a multiple of 39 with the same ending as N.

F. Belohldvek^^ noted that 10A-\-B is divisible by 10p±l if A=FpB is.

C. Borgen'^^ ^oted that Z = a„-10"+ . . . +ai-10+ao is divisible by A^ if

"T' (a_„+rlO''-'+ . . . +a,)(10"-A^)''/''
..=0

is divisible by N. For A'' = 7, take a = 1 ; then 10"— AT = 3 and Z is divisible
by 7 if ao+3ai+2a2 — ^3 — 3a4 — 2a5+ ... is divisible by 7.

J. J. Sylvester^^" noted that, if the r digits of A'^, read from left to right,
be multiplied by the first r terms of the recurring series 1, 4, 3, — 1,-4, — 3;
1, 4, . . . [the residues, in reverse order, of 10, 10^, . . ., modulo 13], the sum
of the products is divisible by 13 if and only if N is divisible by 13.

C. L. Dodgson^^** discussed the quotient and remainder on division by
9 or 11.

L. T. Riess^' noted that, if p is not divisible by 2 or 5, 106+a(a<10)
is divisible by p if b — xa is divisible by p, where mp = 10x-\-a (a< 10) and
m = l, 7, 3, 9 according as p=l, 3, 7, 9 (mod 10), respectively.

A. Loir^^ gave tests for prime divisors < 100 by uniting them by twos
or threes so that the product P ends in 0 1 , as 7 -43 = 30 1 . To test N, multiply
the number formed of the last two digits of A'^ by the number preceding 01 in
P, subtract the product from A^, and proceed in the same manner with the
difference. Then P is a factor if we finally get a difference which is zero.
If a difference is a multiple of a prime factor p of P, then N is divisible by p.

Plakhowo"*^ gave the test by Bougaief, but without using congruences.

'"'Math. Quest. Educ. Times, 57, 1892, 111.

"Assoc, frang. avanc. sc, 22, 1893, II, 240-254.

»M4m. ac. sc. Toulouse, (9), 5, 1893, 459-475.

"La Revue Scientifique de France, (3), 52, 1893, 765

"Casopis, Prag, 23, 1894, 59. "Mature, 57, 1897-8, 54.

«MEducat. Times, March, 1897. Proofs. Math. Quest. Educ. Times, 66, 1897, 108. Cf. W. E.

Heal, Amer. Math. Monthly, 4, 1897, 171-2.
"'^Nature, 56, 1897, 565-6.

«Russ. Nat., 1898, 329. Cf. Jahrb. Fortschritte Math., 29, 1898, 137.
"Assoc, frang. avanc. sc, 27, 1898, II, 144-6.
«»Bull. des sc. math, et phys. 61(§mentaires, 4, 1898-9, 241-3,

1

Chap. XII] CRITERIA FOR DIVISIBILITY. 343

To testiV = ao+Oi-S+ • • • +On5"for the divisor D prime to B, determine d and
X so that Bd = Dx+l. Multiply this equation by Oq and subtract from N.
Thus

N=-BN'-DaoX, N' = aod-\-{ai+a2B-\- . . . +a^B''-^)B.

Hence N is divisible by D if and only if N' is divisible by D. Now, N' is
derived from N by supressing the units digit do and adding to the result the
product aod. Next operate with N' as we did with A^.

J. Malengreau^^ would test N for a factor q prime to 10 by seeking a
multiple 11 ... 1 (to m digits) of q, then an exponent t such that the number
of digits of lO'-A^ is a multiple of m. From each set of m digits of lO'-A^
subtract the nearest multiple of 1 ... 1 (to m digits) . The sum of the resi-
dues is divisible by q if and only if A'' is divisible by q.

G. Loria^^ proved that N = aQ-\-gai-\- . . .-\-g''ak is divisible by a if and
only if a divides the sum ao+ • • . +a^ of the digits of N written to a base g of
the form /ca+ 1 ; or if a divides Oq — ai +02 — • • • when the base g is of the form
ka — 1. Taking g = IC", we have the test, in Gelin's Arithm^tique, in terms
of groups of m digits. We may select m to be |0(a) or a number such that
lO'^il has the factor a. Inplace of 00+^1+ • • . wheng' = 10'", we may employ
pao+Xai + 10Xa2+ . . . +10"-'Xa^_i

+ s\o^™-^(a,^+10a,^+i+ . . . +10"'-'a,^+m-i),

k = l

where X = l, 2 or 5, and p is determined by 10p/X=l (mod o). Taking
a = 7, 13, 17, 19, 23, special tests for divisors are obtained.

G. Loria^^ proved that, if ao, ai,. . . are successive sets of t digits of N,
counted from the right, and o- = ao='=cti+02=^«3+ • • •, then

N-(T = a,{10'=Fl)-\-a2{10^'-l)+as{10^'=pl) + . . .,

so that a factor of 10'=f1 divides A^ if and only if it divides a.
A. Tagiuri^^ extended the last result to any base g. We have

N = ao+ga,+ . . . =Nom+g"'Nr^+g''^N2^-\- . . .

if N,m = o,pm+apm+i9-\- • • • +«pm+m-i^"'"^ Heuce, if 9"^= ± 1 (mod a),

N=Nom^Nim+N2m=^... (mod a).

L. Ripert^" noted that lOD-\-uis divisible by lOS+i if Di—bu is divisible,
and gave many tests for small divisors.

G. Biase^^ derived tests that \Od-\-u has the factor 7 or 19 from

2{l{)d+u)^2u-d (mod 7), 2{lQd+u)=2u+d (mod 19).

O. Meissner^^ reported on certain tests cited above.

"Mathesis, (3), 1, 1901, 197-8.

*^Rendiconti Accad. Lincei (Math.), (5), 10, 1901, sem. 2, 150-8. Mathesis, (3), 2, 1902, 33-39.

"II Boll. Matematica Gior. Sc.-Didat., Bologna, 1, 1902. Cf. A. Bindoni, ibid., 4, 1905, 87.

"Periodico di Mat., 18, 1903, 43-45. ^oL'enseignement math., 6, 1904, 40-46.

"II Boll. Matematica Gior. Sc.-Didat., Bologna, 4, 1905, 92-6.

^''Math. Naturw. Blatter, 3, 1906, 97-99.

344 History of the Theory of Numbers. [Chap, xii

E. NanneF employed ri=Oi — aoX, r2 = a2—riX,. . . (a-<10). Then, if
r„ = 0, A'' = 10"a„4- . . . +10ai+Oo is divisible by lOx-fl and the quotient has
the digits r„_i, r„_2, . . ■ , 7*i, Qo- The cases x = 1, 2 are discussed and several
tests for 7 deduced. For a:= 1/3, we conclude that, if r„ = 0, N is divisible
by 13 and the digits of the quotient are r„_i/3, . . . , r^/S, ao/3.

A. Chiari^ employed D'Alembert's^ method for 10+6, 6 = 3, 7, 9.

G. Bruzzone^^ noted that, to find the remainder R when N is divided by
an integer x of r digits, we may choose y such that x-\-y = 10'', form the
groups of r digits counting from the right of N, and multiply the successive
groups (from the right) hy l,y,y^,. . . or by their residues modulo x; then R
equals the remainder on dividing the sum of the products by x. If we choose
x — y = lO^, we must change alternate signs before adding. For practical use,
take y = l.

Fr. Schuh^^ gave three methods to determine the residue of large numbers
for a given modulus.

Stuyvaert^^ let a, 6, ... be the successive sets of n digits of A'' to the baseB,
so that iV = a+6jB'*+c52''+ rj.^^^ ^ -^ (^^.^isibie ^^y ^ factor D of B''=pR''

if and only if a=^bR''+cR~''^ ... is divisible by D. For R = l, B = 10,
n = 1, 2, . . ., we obtain tests for divisors of 9, 99, 11, 101, etc. A divisor,
prime to B, of niB+l divides N = a+bB if and only if it divides h—ma.

Further Papers Giving Tests for a Given Divisor d.

J. R. Young and Mason for d = l, 13 [Pascal^], Ladies' Diary, 1831, 34-5, Quest.

1512.
P. Gorini [Pascal^], Annali di Fis., Chim. Mat., (ed., Majocchi), 1,1841, 237.
A. Pinaud for d = l, 13, Mem. Acad. Sc. Toulouse, 1, 1844, 341, 347.
*Dietz and Vincenot, Mem. Acad. Metz, 33, 1851-2, 37.
Anonymous writer for d = 9, 11, Jour, fiir Math., 50, 1855, 187-8.
*H. Wronski, Principes de la phil. des math. Cf. de Montferrier, Encyclop^die

math., 2, 1856, p. 95.
O. Terquem for d^l9, 23, 37, 101, Nouv. Ann. Math., 14, 1855, 118-120.
A. P. Reyer for d = l, Archiv Math. Phys., 25, 1855, 176-196.
C. F. Lindman for d = l, 13, ibid., 26, 1856, 467-470.
P. Buttel for d = 7, 9, 11, 17, 19, ibid., 241-266.

De Lapparent [Herter^^], Mem. soc. imp. sc. nat. Cherbourg, 4, 1856, 235-258.
Karwowski [Pascal^], Ueber die Theilbarkeit . . ., II, Progr., Lissa, 1856.
*D. van Langeraad, Kenmerken van deelbarheid der geheele getallen, Schoonho-

ven, 1857.
Flohr, Ueber Theilbarkeit und Reste der Zahlen, Progr., Berlin, 1858.
V. Bouniakowsky for d = 37, 989, Nouv. Ann. Math., 18, 1859, 168.
Elefanti for d = l-n, Proc. Roy. Soc. London, 10, 1859-60, 208.
A. Niegemann for d = 10'"-n+a, Archiv Math. Phys., 38, 1862, 384-8.
J. A. Grunert for d = 7, 11, 13, ibid., 42, 1864, 478-482.
V. A. Lebesgue, Tables diverses pour la decomposition des nombres, Paris, 1864,

p. 13.

"II Pitagora, Palermo, 13, 1906-7, 54-9.

»/6r(f., 14, 1907-8, 35-7.

"/6td., 15, 1908-9, 119-123.

"Supplem. De Vriend der Wiskunde, 24, 1912, 89-103.

"Les Nombres Positifs, Gand, 1912, 59-62.

Chap. XII] CrITEEIA FOR DIVISIBILITY. 345

C. M. Ingleby for d = 9, 11, British Assoc. Report, 35, 1865, 7 (trans.).

M. Jenkins for any prime d, Math. Quest. Educ. Times, 8, 1868, 69, 111.

F. Unferdinger [Gergonnei^], Sitzungsber. Ak. Wiss. Wien (Math.), 59, 1869, II,

465-6.
H. Anton for d = 9, 11, 13, 101, Archiv Math. Phys., 49, 1869, 241-308.
W. H. Walenn, British Assoc. Report, 40, 1870, 16-17 (trans.); Phil. Mag., (4),

36, 1868, 346-8; (4), 46, 1873, 36-41; (4), 49, 1875, 346-351; (5), 2, 1876,

345; 4, 1877, 378; 9, 1880, 56, 121, 271.
M. A. X. Stouff for d< 100, Nouv. Ann. Math., (2), 10, 1871, 104.
J. Lubin, ibid., (2), 12, 1874, 528-30 (trivial).
Szenic for d = 7, 9, 37, Von der Kongruenz der Z., Progr. Schrimm, 1873.

E. Brooks for d = 7, Des Moines Analyst, 2, 1875, 129.

W. J. Greenfield and M. Collins for d = 47, 73, Math. Quest. Educ. Times, 22,
1875, 87.

F. da Ponte Horta for d = 7, 9, 11, 13, Jornal de Sciencias Mat. Ast., 1, 1877, 57-62.
Mennesson for d = 7, Nouv. Corresp. Math., 4, 1878, 151; generahzation by Cesaro,

p. 156.
C. Lange, for d = 7, 13, 17, 19, Ueber die Teilbarkeit der Zahlen, Progr., Berlin, 1879.

F. Jorcke for d = 7, 9, 11, Ueber Zahlenkongruenzen . . ., Progr, Fraustadt, 1878.
K. Broda for any base, Archiv Math. Phys., 63, 1879, 413-428.

A. Badoureau for d = 19, Nouv. Ann. Math., (2), 18, 1879, 35-6.
S. M. Drach for d = 7, Math. Quest. Educ. Times, 35, 1881, 71-2.
W. A. Pick for d = 7, ibid., 38, 1883, 64.

A. Evans for d = 7, Des Moines Analyst, 10, 1883, 134.
K. Haas, Theilbarkeitsregeln . . ., Progr., Wien, 1883.

G. Wertheim, Elemente der Zahlentheorie, 1887, 31-33.

B. Adam for d<100, Ueber die Teilbarkeit. . ., Progr. Gym. Clausthal, 1889.
A. Loir for d<138. Jour, de math, elem., 1889, 66, 107-10, 121-3.

A. G. Fazio [SchlegeP^], Sui caratteri. . ., Palermo, 1889.

E. Gelin, Mathesis, (2), 2, 1892, 65, 93; (2), 12, 1902, 65-74, 93-99 (extract in

Mathesis, (3), 10, 1910, Suppl. I); Ann. Soc. Sc. Bruxelles, 34, 1909-10, 66;

Recueil de problemes d'arith., 1896. Extracts by M. Nasso, Revue de Math.

(ed., Peano), 7, 1900-1, 42-52.
Speckmann, Dorsten, Haas, Dorr, Zeitschrift Math. Phys., 37, 1892, 58, 63,

128, 192, 383.
Lalbaletrier, Jour, de Math, (ed., de Longchamps), 1894, 54.
H. T. Burgess [Pascal*], Nature, 57, 1897-8, 8-9, 30, 55.
A. Conti [Pascal*], Periodico di Mat., 13, 1898, 180-6, 207-9.

F. Mariantoni, ibid., 149-151, 191-2, 217-8.

T. Lange for d<30, Archiv. Math. Phys., (2), 16, 1898, 220-3.

W. J. Greenstreet, Math. Gazette, 1, 1900, 186-7.

Christie for d = 2^p,5'^p (p prime). Math. Quest. Educ. Times, 73, 1900, 119.

A. Cunningham and D. Biddle for d = rp=i=l, ibid., 75, 1901, 49-50.
M. Zuccagni for d = 7, Suppl. al Periodico di Mat., 6, fasc. V.
Calvitti for d = 7, ibid., 8, fasc. IV.

S. Dickstein, Wiad. Mat., Warsaw, 6, 1902, 253-7 (Pohsh).

B. Niewenglowski, ibid., 252-3.

Pietzker ford = 7, 11, 13, 27, 37, Unterrichtsblatter Math. Naturwiss., 9, 1903,

85-110.
A. Church for d = 7, 13, 17, Amer. Math. Monthly, 12, 1905, 102-3.
E. A. Cazes, Assoc, frang., 36, 1907, 55-63.
A. Gerardin for d = 7, 13, 17, 37, 43, Sphinx-Oedipe, 1907-8, 2.
M. Morale for d = 7, Suppl. al Periodico di Mat., 11, 1908, 103.
*T. Ghezzi, ibid., 12, 1908-9, 129-130.
Lenzi, II Boll. Matematica Gior. Sc.-Didat., 7, 1908.

346 History of the Theory of Numbers. [Chap, xiii

R. Polpi, ibid., 8, 1909, 281-5.

M. Morale for d = 7, 13, Suppl. al Periodico di Mat., 13, 1909-10, 38-9.

A. L. Csada, ibid., 56-8.

*A. La Paglia, ibid., 14, 1910-11, 136-7, extension of Morale to any d.

A. V. Filippov, 8 methods for d = 9, Kagans Bote, 1910, 88-92, No. 520.

P. Cattaneo for rf= 11, II Boll. Matematica Gior. Sc.-Didat., 9, 1910, 305-6.

*L. Miceli, Condizioni di divisibility di un numero N per un numero a . . . , Matera,

1911, 8 pp.
R. Ayza for d = a-10''±l, Revista sociedad mat. espanola, Madrid, 1, 1911, 162-6.
*Paoletti, II Pitagora, Palermo, 18, 1911-12, 128-132.
*R. La Marca, Criteri di congruenza e criteri di divisibilita, Torre del Greco, 1912,

30 pp.
K. W. Lichtenecker, Zeitschr. fur Realschulwesen, 37, 1912, 338-49.
R. E. Cicero, Sociedad Cientifica Antonio Alzate, 32, 1912-3, 317-331.
J. G. Gal6 for d = 7, Revista sociedad mat. espanola, 3, 1913-4, 46-7. ..

C. F. lodi for d = 7, 13, 17, 19, Suppl. al Periodico di Mat., 18, 1914, 20-3. >

E. Kylla for d=ll, Unterrichtsblatter Math. Naturwiss., 20, 1914, 156.
R. Krahl for d = 7, Zeitschrift Math. Naturw. Unterricht, 45, 1914, 562.
P. A. Fontebasso, II Boll. Matematica, 13, 1914-5.
G. M. Persico, Periodico di Mat., 32, 1917, 105-124.
Sammlung der Aufgaben in Zeitschrift Math. Naturw. Unterricht, 1898: ford=7,

II, 337; IV, 404, 407; for d = 9, 11, XXIV, 606; XXV, 587-8; for d = 37,
etc., XXVI, 18, 25-27.

Criteria for di\dsibility in connection with tables were given by Barlow ,^^
Tarry«6 ^nd Lebon" of Ch. XIII, and Harmuth^^ of Ch. XIV.

Papers on Divisibility not Available for report.

Joubin, Jour. Acad. Soc. Sc. France et de I'Etranger, Paris, 2, 1834, 230.

J. Lenth^ric, Th^orie de la divisibility des nombres, Paris, 1838.

R. Volterrani, Saggio sulla divisione ragionata dei n. interi, Pisa, 1871.

F. Tirelli, Teoria della divisibilita de' numeri, Napoli, 1875.
E. Tiberi, Teoria generale sulle condizioni di divisibility . . . , Arezzo, 1890.
J. Kroupa, Casopis, Prag, 43, 1914, 117-120.

G. Schroder, Unterrichtsblatter fiir Math. Naturwiss., 21, 1915, 152-5.

CHAPTER XIII.

FACTOR TABLES. LISTS OF PRIMES.

Eratosthenes (third century B.C.) gave a method, called the sieve or
crib of Eratosthenes, of determining all the primes under a given limit I,
which serves also to construct the prime factors of numbers <l. From
the series of odd numbers 3, 5, 7, ... , strike out the square of 3 and every
third number after 9, then the square of 5 and every fifth number after 25,
etc. Proceed until the first remaining number, directly following that one
whose multiples were last cancelled, has its square >l. The remaining
numbers are primes.

Nicomachus and Boethius^ began with 5 instead of with 5^, 7 instead of
with 7^, etc., and so obtained the prime factors of the numbers <l.

A table containing all the divisors of each odd number ^113 was printed
at the end of an edition of Aratus, Oxford, 1672, and ascribed to Eratos-
thenes by the editor, who incorrectly considered the table to be the sieve of
Eratosthenes. Samuel Horsley^ believed that the table was copied by
some monk in a barbarous age either from a Greek commentary on the
Arithmetic of Nicomachus or else from a Latin translation of a Greek
manuscript, published by Camerarius, in which occurs such a table to 109.

Leonardo Pisano^ gave a table of the 21 primes from 11 to 97 and a
table giving the factors of composite numbers from 12 to 100; to determine
whether n is prime or not, one can restrict attention to divisors ^ ^/n.

Ibn Albanna in his Talkhys^ (end of 13th century) noted that in using
the crib of Eratosthenes we may restrict ourselves to numbers ^ -y/l.

Cataldi^ gave a table of all the factors of all numbers up to 750, with a
separate list of primes to 750, and a supplement extending the factor table
from 751 to 800.

Frans van Schooten® gave a table of primes to 9979.

J. H. Rahn^ (Rhonius) gave a table of the least factors of numbers, not
divisible by 2 or 5, up to 24000.

T. Brancker^ constructed a table of the least divisors of numbers, not
divisible by 2 or 5, up to 100 000. [Reprinted by Hinkley.^^]

*Introd. in Arith. Nicomachi; Arith. Boethii, lib. 1, cap. 17 (full titles in the chapter on perfect
numbers). Extracts of the parts on the crib, with numerous annotations, were given by
Horsley.2 Cf. G. Bernhardy, Eratosthenica, Berlin, 1822, 173-4.

2Phil. Trans. London, 62, 1772, 327-347.

311 Liber Abbaci di L. Pisano (1202, revised 1228), Roma, 1852, ch. 5; Scritti, 1, 1857, 38.

*Transl. by A. Marre, Atti Accad. Pont. Nuovi Lincei, 17, 1863-4, 307.

"Trattato de' numeri perfetti, Bologna, 1603. Libri, Histoire des Sciences Math, en Italic,
ed. 2, vol. 4, 1865, 91, stated erroneously that the table extended to 1000.

«Exercitat. Math., libri 5, cap. 5, p. 394, Leiden, 1657.

^Algebra, Zurich, 1659. WaUis,!"* p. 214, attributed this book to John Pell.

*An Introduction to Algebra, translated out of the High-Dutch [of Rahn's' Algebra] into
EngHsh by Thomas Brancker, augmented by D. P. [=Dr. Pell], London, 1668. It is
cited in Phil. Trans. London, 3, 1668, 688. The Algebra and the translation were de-
scribed by G. Wertheim, BibUotheca Math., (3), 3, 1902, 113-126.

347

348 History of the Theory of Numbers. (Chap, xiii

D. Schwenter^ gave all the factors of the odd numbers < 1000.

John Wallis^° gave a list of errata in Brancker's^ table.

John Harris," D. D., F. R. S., reprinted Brancker's^ table.

De Traytorens^^ emphasized the utility of a factor table. To form a
table showing all prime factors of numbers to 1000, begin by multiplying
2, 3, .. . by all other primes < 1000, then multiply 2X3 by all the primes,
then 2X3X5, etc.

Joh. Mich. Poetius^^ gave a table (anatomiae numerorum) of all the
prime factors of numbers, not divisible by 2, 3, 5, up to 10200. It was
reprinted by Christian Wolf," Willigs,^^ and Lambert. ^-

Johann Gottlob Krliger^* gave a table of primes to 100 999 (not to 1
million, as in the title), stating that the table was computed by Peter
Jager of Niirnberg.

James Dodson^® gave the least di\'isors of numbers to 10000 not divisible
by 2 or 5 and the primes from 10000 to 15000.

Etienne FranQois du Tour^^ described the construction of a table of all
composite odd numbers to 10000 by multiplying 3, 5, ... , 3333 by 3, ... , 99.

Giuseppe Pigri^^ gave all prime factors of numbers to 10000.

Michel Lorenz Willigs^^ (Willich) gave all di\dsors of numbers to 10000.

Henri Anjema-° gave all divisors of numbers to 10000.

Rallier des Ourmes-^ gave as if new the sieve of Eratosthenes, placing
3 above 9 and every third odd number after it, a 7 above 49, etc. He
expressed each number up to 500 as a product of powers of primes.

J. H. Lambert^^ described a method of making a factor table and gave
Poetius'^^ table and expressed a desire for a table to 102 000. Lagrange
called his attention to Brancker's^ table.

Lambert-^ gave [Ivriiger's^^] table showing the least factor of numbers
not di\'isible by 2, 3, 5 up to 102000, and a table of primes to 102 000, errata
in which were noted by KliigeP^.

•Geometria Practica, Numb., 1667, I, 312.

loTreatise of Algebra, additional treatise, Ch. Ill, §22, London, 1685.
"Lexicon Technicum, or an Universal English Dictionary of Arts and Sciences, London, vol. 2,

1710 (under Incomposite Numbers). In ed. 5, London, 2, 1736, the table was omitted,

but the text describing it kept. WaUis, Opera, 2, ,511, listed 30 errors.
"Histoire de I'Acad. Roy. Science, ann6e 1717, Paris, 1741, Hist., 42-47.
"Anleitung zu der Arith. Wissenschaft vermittelst einer parallel Algebra, Frkf . u. Leipzig, 1728.
"VoUst. Math. Lexicon, 2, Leipzig, 1742, 530.
'*Gedancken von der Algebra, nebst den Primzahlen von 1 bis 1 000 000, Halle im Magd., 1746,

Cf. Lambert. ^a
"The Calculator. . .Tables for Computation, London, 1747.
•"Histoire de I'Acad. Ro>. Sc, Paris, ann6e 1754, Hist., 8&-90.
"Nuove tavole degli elementi dei numeri dall' 1 al 10 000, Pisa, 1758.
"Griindhche Vorstellung der Reesischen allgemeinen Regel . . . Rechnungsarten, Bremen u.

Gottingen, 2, 1760, 831-976.
^Table des diviseurs de tous les nombres naturels, depuis 1 jusqu'4 10 000, Leyden, 1767, 302 pp.
"M^m. de math, et de physique, Paris, 5, 1768, 485-499.

"Bej-trage znm Gebrauche der Math. u. deren Anwendung, Berlin, 1770, II, 42.
"Zusatze zu den logarithm ischen imd trig. Tabellen, BerUn, 1770.
"Math. Worterbuch, 3, 1808, 892-900.

Chap. XIII] FACTOR TABLES, LiSTS OF PrIMES. 349

J. Ozanam^^ gave a table of primes to 10000.

A. F. Marci^^ gave in 1772 a list of primes to 400 000.

Jean Bernoulli^^" tabulated the primes 16n+l up to 21601.

L. Euler" discussed the construction of a factor table to one miUion.
Given a prime p = 30a±i (^ = 1, 7, 11, 13), he determined for each r = l, 7,
11, 13, 17, 19, 23, 29, the least q for which SOq+r is divisible by p, and
arranged the results in a single table with p ranging over the primes from
7 to 1000. He showed how to use this auxiliary table to construct a factor
table between given limits.

C. F. Hindenburg^^ employed in the construction of factor tables a
"patrone" or strip of thick paper with holes at proper intervals to show
the multiples of p, for the successive primes p.

A. FelkeP^ gave in 1776 a table of all the prime factors (designated by
letters or pairs of letters) of numbers, not divisible by 2, 3, or 5, up to
408 000, requiring for entry two auxiliary tables. In manuscript^", the
table extended to 2 million; but as there were no purchasers of the part
printed, the entire edition, except for a few copies, was used for cartridges
in the Turkish war. The imperial treasury at Vienna, at the cost of which
the table was printed, retained the further manuscript. [See Felkel.^^]

L. Bertrand^^ discussed the construction of factor tables.

The Encyclopedie of d'Alembert, ed. 1780, end of vol. 2, contains a
factor table to 100 000.

Franz Schaffgotsch^^ gave a method, equivalent to that of a stencil for
each prime p, for entering the factor p in a factor table with eight headings
SOm+k, /c = 1, 7, 11, 13, 17, 19, 23, 29, and hence of numbers not divisible by
2, 3, or 5. Proofs were given by Beguelin and Tessanek, ibid., 362, 379.

The strong appeals by Lambert^^ that some one should construct a fac-
tor table to one million led L. Oberreit, von Stamford, Rosenthal, Felkel,
and Hindenburg to consider methods of constructing factor tables and to
prepare such tables to one million, with plans for extension to 5 or 10

^^Recreations Math., new ed., Paris, 1723, 1724, 1735, etc., I, p. 47.

^^Primes "in quater centenis millibus," Amstelodami, 1772.

26aNouv. M6m. Ac. Berlin, ann^e 1771, 1773, 323.

"Novi Comm. Acad. Petrop., 19, 1774, 132; Comm. Arith., 2, 64.

''^Beschreibung einer ganz neuen Art nach einem bekannten Gesetze fortgehende Zahlen durch

Abzahlen oder Abmessen bequem u. sicher zu finden. Nebst Anwendung der Methode

auf verschiedene Zahlen, besonders auf eine damach zu fertigende Factorentafel . . . ,

Leipzig, 1776, 120 pp.
2*Tabula omnium factorum simphcium, numerorum per 2, 3, 5 non divisibilium ab 1 usque

10 000 000 [!]. Elaborata ab Antonio Felkel. Pars I. Exhibens factores ab 1 usque

144 000, Vindobonae, 1776. Then there is a table to 408 000, given in three sections.

There is a copy of this complete table in the Graves Library, University College, London.

Tafel aller einfachen Factoren der durch 2, 3, 5 nicht theilbaren Zahlen von 1 bis 10 000 000.

Entworfen von Anton Felkel. I. Theil. Enthaltend die Factoren von 1 bis 144 000,

Wien, 1776. There is a copy of this incomplete table in the hbraries of the Royal Society

of London and Gottingen University.
"Cf. Zach's Monatliche Correspondenz, 2, 1800, 223; Allgemeine deutsche BibUothek, 33, II, 495.
'^Develop, nouveau de la partie ^1. math., Geneve, 1774.
'''Gesetz, welches zur Fortsetzung der bekannten Pellischen Tafehi dient, Abhand. Privatgesell-

schaft in Bohmen, Prag, 5, 1782, 354-382.

350 History of the Theory of Numbers. [Chap, xiii | '^ '

million. Their extended correspondence with Lambert^^ was published.
Of the tables constructed by these computers, the only one published is that
by Felkel.-^ The history of their connection with factor tables has been
treated by J. W. L. Glaisher.^

Johann Neumann^^ gave all the prime factors of numbers to 100 100.

Desfaviaae gave a like table in the same year.

F. Maseres^^ reprinted the table of Brancker.^

G. Vega^^ gave all the prime factors of numbers not divisible by 2, 3, or 5
to 102 000 and a list of primes from 102 000 to 400 031. Chernac hsted errors
in both tables. In Hiilsse's edition, 1840, of Vega, the Ust of primes extends
to 400 313.

A. Felkel,^^ in his Latin translation of Lambert's'^^ Zusatze, gave all the
prime factors except the greatest of numbers not divisible by 2, 3, 5 up to
102 000, large primes being denoted by letters. In the preface he stated
that, being unable to obtain his extensive manuscript^" in 1785, he calculated
again a factor table from 408 000 to 2 856 000.

J. P. Griison^^ gave all prime factors of numbers not divisible by 2, 3, 5
to 10500. He^^'' gave a table of primes to 10000.

F. W. D. Snell^° gave the prime factors of numbers to 30000.

A. G. Kastner^^ gave a report on factor tables.

K. C. F. Krause'*- gave a table of 22 pages showing all products < 100 000
of two primes, a table of primes < 100 000 with letters for 01, 03, ... , 99,
and (pp. 25-28) a factor table to 10000 by use of letters for numbers < 100.

N. J. Lidonne^^ gave all prime factors of numbers to 102 000.

Jacob Struve"*^" made a factor table to 100 by de Traytorens'^^ method.

L. Chernac^ gave all the prime factors of numbers, not divisible by
2, 3 or 5, up to 1 020 000.

J. C. Burckhardt*^ gave the least factor of numbers to 3 million. He did
not compute the first million, but compared Chernac's table with a manu-
script (mentioned in Briefwechsel,^^ p. 140) by Schenmarck which extended
to 1 008 000. Cf. iVIeissel.''^

^'Joh. Heinrich Lamberts deutscher gelehrter Briefwechsel, herausgegeben von Joh. Bernoulli,

Berlin, 1785, Leipzig, 1787, vol. 5. "Proc. Cambridge Phil. Soc, 3, 1878, 99-138.

'^Tabellen der Primzahlcn und der Faktoren der Zahlen, welche unter 100 100, und durch 2, 3

Oder 5 nicht theilbar sind, Dessau, 1785, 200 pp.
'*The Doctrine of Permutations and Combinations. . ., London, 1795.
'^Tabulae logarithmico-trigonometricae, 1797, vol. 2.
**J. H. Lambert, Supplementa tab. log. trig., Lisbon, 1798.
"Pinaeoth6que, ou collection de Tables. . ., Berlin, 1798.
''"Enthiillte Zaubereyen u. Geheimnisse d. Arith., Berlin, 1796, I, 82-4.
*°Ueber eine neue und bequeme Art, die Factorentafeln einzurichten, nebst einer Kupfertafel

der einfachen Factoren von 1 bis 30000, Gicssen and Darmstadt, 1800.
"Fortsetzung der Rechenkunst, ed. 2, Gottingen, 1801, 566-582.

^'Factoren- und Primzahlentafel von 1 bis 100 000 neu berechnet, Jena u. Leipzig, 1804.
"Tables de tous les diviseurs des nombres < 102 000, Paris, 1808.
^'''Handbuch der Math., Altona, II, 1809, 108.
**Cribrum Arithmeticum . . . Daventriae, Isil, 1020 pp. Reviewed by Gauss, Gottingische

gelehrte Anzeigen, 1812; Werke 2, 181-2. Errata, Cunningham.*'
"Tables des diviseurs. . . 1 ^ 3 036 000, Paris, 1817, 1814, 1816 (for the respective three milliona),

and 1817 (in one volume).

•'I;i Chap. XIII] FACTOR TABLES, LiSTS OF PrIMES. 351

P. Barlow^® gave the prime and power of prime factors of numbers to
10000 and a list of primes to 100 103.

C. Hutton^^ gave the least factor of numbers to 10000.

Rees' Cyclopaedia, 1819, vol. 28, Hsts the primes to 217 219.

Peter Barlow^^ gave a two-page table for finding factors of a number
iV< 100 000. The primes p = 7 to p = 313 are at the head of the columns,
while the 18 numbers 1000, . . . , 9000, 10000, 20000, . . . , 90000 are in the left-
hand column. In the body of the table is the remainder of each of the
latter when divided by the primes p. To test if p is a factor of N, add its
last two digits to the remainders in the line of hundreds and thousands in
the column headed p and test whether the sum is divisible by p.

J. P. Kulik'^^ gave a factor table to 1 million.

J. HantschP° gave a factor table to 18277; J. M. Salomon,^^ to 102 Oil.

A. L. Crelle^^ gave the number of primes 4n+ 1 and the number of primes
4n+3 in each thousand up to the fiftieth.

A. Guyot^^ hsted the primes to 100 000.

A. F. Mobius,^^" using square ruled paper, inserted from right to left
0, 1, 2, ... in the top row of cells, and inserted n in each cell of the nth row
below the top row whenever the corresponding number in the top row is
divisible by n. We thus have a factor table. Certain numbers of the table
Ue in straight lines, others in parabolas, etc.

P. A. G. Colombier^^^ discussed the determination of the primes <V,
given those < I.

H. G. Kohler'^ gave a factor table to 21524.

E. Hinkley^^ gave a factor table to 100 000, listing all factors of odd
numbers to 20000 and of even numbers to 12500.

F. Schallen^^"gave the prime and prime-power factors of numbers < 10000.
F. Landry^*^ gave factor and prime tables to 10000.
A. L. Crelle^^ discussed the expeditious construction of a factor table, and

in particular a method of extending Chernac's^ table to 7 million.
J. HoiieP^ gave a factor table to 10841.
Jacob Philip Kulik (1773-1863) spent 20 years constructing a factor

*^New Mathematical Tables, London, 1814. Errata, Cunningham.^

<Thil. and Math. Dictionary, 1815, vol. 2, 236-8.

^8New Series of Math. Repository (ed., Th. Leybourn), London, 4, 1819, II, 30-39.

^'Tafeln der einfachen Faktoren aUer Zahlen unter 1 million, Graz, 1825.

60Log.-trig. Handbuch, Wien, 1827. "Log. Tafeln, Wien, 1827.

^2Jour. fur Math., 10, 1833, 208.

'^Thdorie g^nerale de la divisibihte des nombres, suivie d'applications varices et d'une table de

nombres premiers compris entre 0 et 100 000, Paris, 1835.
63a Jour, fvir Math., 22, 1841, 276-284. "^Nouv. Ann. Math., 2, 1843, 408-410.

"Log.-trig. Handbuch, Leipzig, 1848. Errata, Cunningham.**
^^Tables of the prime numbers and prime factors of the composite numbers from 1 to 100 000,

Baltimore, 1853. Reproduction of Brancker's* table.
ssaprirjizahlen-Tafel von 1 bis 10000. . ., Weimar, 1855. For 99 errata, see Cunningham.*^
6*Tables des nombres entiers non divisibles par 2, 3, 5, et 7, jusqu' k 10201, avec leurs diviseurs

simples en regard, et des carres des 1000 premiers nombres, Paris, 1855. Tables des

nombres premiers, de 1 £l 10000, Paris, 1855.
"Jour, ftir Math., 51, 1856, 61-99. "Tables de log., Paris, 1858.

352 History of the Theory of Numbers. [Ch.u'. xiii

table to 100 million; the manuscripts^ has been in the library of the Vienna
Royal Academy since 1867. Lehmer^- gave an account of the first of the
eight volumes of the manuscript, listed 226 errors in the tenth million, and
concluded that Kulik's manuscript is certainly not accurate enough to
warrant publication, though of inestimable value in checking a newly
constructed table. Lehmer^^ gave a further account of this manuscript
which he examined in Vienna. Volume 2, running from 12 642 600 to
22 852 800 is missing. The eight volumes contained 4,212 pages.

B. Goldberg*^" gave all factors of numbers prime to 2, 3, 5, to 251 647.
Zacharias Dase,^^ in the introduction to the table for the seventh million,

printed a letter from Gauss, dated 1850, giving a brief history- of previous
tables and referring to the manuscript factor table for the fourth, fifth and
sixth milUons presented to the Berlin Academy by A. L. Crelle. Although
Gauss was confident this manuscript would be pubhshed, and hence urged
Dase to undertake the seventh million, etc., the Academy found the manu-
script to be so inaccurate that its publication was not ad\'isable. Dase died
in 1861 lea\'ing the seventh million complete and remarkably accurate,
the eighth nearly complete, and a large part of the factors for the ninth and
tenth millions. The work was completed by Rosenberg, but ^vith numerous
errors. The table for the tenth million has not been printed ; the manuscript
was presented to the Berlin Academy in 1878, but no trace of it was found
when Lehmer^- desired to compare it with his table of 1909.

C. F. Gauss^- gave a table showing the number of primes in each thousand
up to one million and in each ten thousand from one to three million, with a
comparison with the approximate formula jdx/log x.

V. A. Lebesgue^^ discussed the formation of factor tables and gave that
to 115500 constructed by Hoiiel.

W. H. Oakes^ used a complicated apparatus consisting of three tables on
six sheets of various sizes and nine perforated cards (cf. Committee, ^^ p. 39).

W. B. Da\as^s considered numbers in the vicinity of 10^, and of 10^^

E. MeisseP^ computed the number of primes in the successive sets of
100 000 numbers to one million and concluded that Burckhardt's*^ table
gives correctly the primes to one million.

••Cited by Kulik. Abh. Bohm. Gesell. Wiss., Prag, (5), 11, 1860, 24, footnote. A report on the
manuscript was made by J. Petzval, Sitzungsberichte Ak. Wiss. Wien (Math.), 53, 1866,
II, 460. Cited by J. Perott, I'interm^iaire des math., 2, 1895, 40; 11, 1904, 103.

•"Primzahlen- u. Faktortafeln von 1 bis 251 647, Leipzig, 1862. Errata, Cunningham."

•'Factoren-Tafeln fur alle Zahlcn der siebenten MilUon . . . , Hamburg, 1862; . . .der achten Mil-
Uon, 1863;. . .der neuhten MilUon (erganzt von H. Rosenberg), 1865.

•^Posthumous manuscript, Werke, 2, 1863, 435-447.

••Tables diverses pour la decomposition des nombres en leurs facteurs premiers, M6m. soc. sc.
phys. et nat. de Bordeaux, 3, cah. 1, 1864, 1-37.

•♦Machine table for determining primes and the least factors of composite numbers up to
100 000, London, 1865.

••Jour.de Math., (2), 11, 1866, 188-190; Proc. London Math. Soc, 4, 1873, 416-7. Math.
Quest. Educ. Times, 7, 1867, 77; 8, 1868, 30-1.

••Math. Annalen, 2, 1870, 63&-642. Cf. 3, p. 523; 21, 1883, p. 304; 25, 1885, p. 251.

I

Chap. XIII] FACTOR TABLES, LiSTS OF PRIMES. 353

J. W. L. Glaisher" gave for the second and ninth millions the number of
primes in each interval of 50000 and a comparison with lix' — lix, where
lix = jdx/log X [more precise definition at the end of Ch. XVIII].

A committee^^ consisting of Cayley, Stokes, Thompson, Smith, and
Glaisher prepared the Report on Mathematical Tables, which includes
(pp. 34-9) a list of factor and prime tables.

J. W. L. Glaisher^^ described in detail the method used by his father^"
and gave an account of the history of factor tables.

Glaisher^^" enumerated the primes in the tables of Burckhardt and Dase.

Glaisher^^^ tabulated long sets of consecutive composite numbers. He^^"
enumerated the prime pairs (as 11, 13) in each successive thousand to 3
million and in the seventh, eighth, and ninth millions.

E. Lucas^^'' wrote P(q) for the product of all the primes ^ q, where q
is the largest prime < n. If xP(g)±l are both composite, xP{q)—n,. . .,
xP{q),. . ., xP{q)-\-n give 2n+l composite numbers.

Glaisher^^' enumerated the primes 4n4-l and the primes 4n+3 for inter-
vals of 10000 in the kth milUon for k = l,2, 3, 7, 8, 9.

James Glaisher'^° filled the gap between the tables by Burckhardt^^ and
Dase". The introduction to the table for the fourth million gives a history
of factor tables and their construction. Lehmer^^ praised the accuracy of
Glaisher's table, finding in the sixth million a single error besides two mis-
prints.

Tuxen'^^ gave a process to construct tables of primes.

Groscurth and Gudila-Godlewksi, Moscow, 1881, gave factor tables.

*V. Bouniakowsky'^^" gave an extension of the sieve of Eratosthenes.

W. W. Johnson'^^'' repeated Glaisher's'^° remarks on the history of tables.

P. Seelhoff^^ gave large primes /c-2"+l {k< 100) and composite cases.

Simony'^^ gave the digits to base 2 of primes to 2^^ = 16384.

L. Saint-Loup^^ gave a graphical exposition of Eratosthenes' sieve.

H. Vollprecht'^^ discussed the construction of factor tables.

"Report British Association for 1872, 1873, trans., 19-21. Cf. W. W. Johnson, Des Moines

Analyst, 2, 1875, 9-11.
68Report British Association for 1873, 1874, pp. 1-175. Continued in 1875, 305-336; French

transl., Sphinx-Oedipe, 8, 1913, 50-60, 72-79; 9, 1914, 8-14.
"Proc. Cambridge Phil. Soc, 3, 1878, 99-138, 228-9.
69'»/6id., 17-23, 47-56; Report British Assoc, 1877, 20 (sect.). Extracts by W. W. Johnson,

Des Moines Analyst, 5, 1878, 7.
s'^-Messenger Math., 7, 1877-8, 102-6, 171-6; French transl., Sphinx-Oedipe, 7, 1912, 161-8.
^^'^Ibid., 8, 1879, 28-33.
«9«*/6id., p. 81. C. Gill, Ladies' Diary, 1825, 36-7, had noted that xP(q)+j is composite for

j = 2,...,q-l.
BseReport British Assoc, 1878, 470-1; Proc. Roy. Soc. London, 29, 1879, 192-7.
^"Factor tables for the fourth, fifth and sixth millions, London, 1879, 1880, 1883.
"Tidsskrift for Mat., (4), 5, 1881, 16-25.

'i«Memoirs Imperial Acad. Science, St. Petersburg, 41, 1882, Suppl, No. 3, 32 pp.
"^Annals of Math., 1, 1884-5, 15-23.

"Zeitschrift Math. Phys., 31, 1886, 380. Reprinted, Sphinx-Oedipe, 4, 1909, 95-6.
"Sitzungsber. Ak. Wiss. Wien (Math.), 96, II, 1887, 191-286.
^^Comptes Rendus Paris, 107, 1888, 24; Ann. de I'^cole norm., (3), 7, 1890, 89-100.
"Ueber die Herstellung von Faktorentafehi, Diss. Leipzig, 1891.

354 History of the Theory of Numbers. [Chap, xiii

C. A. Laisant'^^" would exhibit a factor table by use of shaded and un-
shaded squares on square-ruled paper without using numbers for entries.

G. Speckmann'^'' made tri\aal remarks on the construction of a list of
primes.

P. Valerio'® arranged the odd numbers prime to 5 in four columns
according to the endings 1, 3, 7, 9. From the first column cross out the first
multiple 21 of 3, then the third following number 51, etc. Similarly for the
other columns. Then use the primes 7, 11, etc., instead of 3.

J. P. Gram" pubhshed the computation by N. P. Bertelsen of the
number of primes to ten million in intervals of 50000 or less, which led to
the detection of numerous errors in the tables of Burckhardt^^ and Dase."

G. L. Bourgerel"^ gave a table with 0, 1, . . . , 9 in the first row, 10, . . . , 19
in the second row (with 10 under 0), etc. Then all multiples of a chosen
number lie in straight lines forming a paralellogram lattice, with one branch
through 0. For example, the multiples of 3 appear in the Une through 0, 12,
24, 36, ... , the parallel through 3, 15, 27, ... , the parallel 21, 33, 45, ... ; also
in a second set of parallels 3, 12, 21, 30; 6, 15, 24, 33, 42, 51, 60; etc.

E. Suchanek" continued to 100 000 Simony's^^ table of primes to base 2.

D. von Sterneck^" counted the number of primes 100 n-|- 1 in each tenth of
a million up to 9 million and noted the relatively small variation from one-
fortieth of the total number of primes in the interval.

H. Vollprecht^^ discussed the determination of the number of primes <N
by use of the primes < v^-

A. Cunningham and H. J. WoodalP^ discussed the problem to find all
the primes in a given range and gave many successive primes >9 million.

They^^a ^^^^^^ jj^y primes between 224±1020.

H. Schapira^^'' discussed algebraic operations equivalent to the sieve of
Eratosthenes.

*V. Di Girio, Alba, 1901, applied indeterminate analysis of the first
degree to define a new sieve of Eratosthenes and to factoring.

John Tennant^ wrote numbers to the base 900 and used auxiliary tables.

A. Cunningham^" gave long lists of primes between 9-10^ and 10^^

Ph. Jolivald^ noted that a table of all factors of the first 2n numbers
serves to tell readily whether a number <4n+2 is prime or not.

^'"Assoc. frang., 1891, II, 165-8. 7**Archiv Math. Phys., (2), 11, 1892, 439-441.

'«La revue scientifique de France, (3), 52, 1893, 764-5.

"Acta Math., 17, 1893, 301-314. List of errors reproduced in Sphinx-Oedipe, 5, 1910, 49-51.

^*La revue scientifique de France, (4), 1, 1894, 411-2.

"Sitzunpsber. Ak. Wiss. Wien (Math.), 103, II a, 1894, 443-610.

'"Anzeiger K. Akad. Wiss. Wien (Math.), 31, 1894, 2-4. Cf. Kronecker, p. 416 below.

"Zeitschrift Math. Phys., 40,. 1895. 118-123.

"Report British Assoc, 1901, 553; 1903, 561; Messenger Math., 31, 1901-2, 165; 34, 1904-5,
72, 184; 37, 1907-8, 6.5-83; 41, 1911, 1-16. s^^Report British Assoc, 1900, 646.

»«'Jahresber. d. Deutschen Math. Verein., 5, 1901, I, 69-72.

"Quar. Jour. Math., 32, 1901, 322-342.

»*^Ibid., 35, 1903, 10-21; Mess. Math., 36, 1907, 145-174; 38, 1908, 81-104; 38, 1909, 145-175;
39, 1909, 33-63, 97-128; 40, 1910, 1-36; 45, 1915, 49-75; Proc London Math. Soc, 27,
1896, 327; 28, 1897, 377-9; 29, 1898, 381-438, 518; 34, 1902, 49.

•♦L'intermfidiaire des math., 11, 1904, 97-98.

Chap. XIII] FaCTOK TaBLES, LiSTS OF PRIMES. 355

A. Cunningham^^ noted errata in various factor tables.

*J. R. Akerlund^^" discussed the determination of primes by a machine.

Gaston Tarry^^ would use an auxiliary table (as did Barlow in 1819)
to tell by the addition of two entries (< |p) if a given number < iV is divisible
by a chosen prime p. For N = 10000, he used the base 6 = 100, and gave a
table showing the numerically least residues of the numbers r<h and the
multiples of b for each prime p<b. Then nh-\-r is divisible by p if the
residues of nh and r are equal and of opposite sign. For A^ = 100 000, he
used 6 = 60060 = 2-91-330 and wrote numbers in the form m6+330g+r,
q<90, r<330; or, again, 6 = 20580. Ernest Lebon" used such tables with
the base 30030 = 2-3-5-7-lM3, or its product by 17.

Ernest Lebon,^^ J. Deschamps,^^ and C. A. Laisant^'''' discussed the con-
struction of factor tables.

J. C. Morehead^° extended the sieve of Eratosthenes to numbers
ma^+6 (m = l, 2, 3,. . .) in any arithmetical progression. The case a = 2,
6= ±1, is discussed in detail, with remarks on the construction of a table
to serve as a factor table for numbers m-2''=t 1.

L. L. Dines^^ treated the case a = 6, 6 = =fcl, and the factorization of
numbers m-Q'^^l.

D. N. Lehmer^^ gave a factor table to 10 million and listed the errata in
the tables by Burckhardt, Glaisher, Dase, Dase and Rosenberg, and
Kulik's tenth million, and gave references to other (shorter) lists of errata.

E. B. Escott^^" listed 94 pairs of consecutive large numbers all of whose
prime factors are small.

L. Aubry^^° proved that a group of 30 consecutive odd numbers does not

contain more than 15 primes or numbers all of whose prime factors exceed 7.

Cunningham^^" listed the numbers of 5 digits with prime factors ^ 11 .

85Messenger Math., 34, 1904-5, 24-31; 35, 1905-6, 24.

ss^Nyt Tidsskrift for Mat., Kjobenhavn, 16A, 1905, 97-103.

8«Bull. Soc. Philomathique de Paris, (9), 8, 1906, 174-6, 194-6; 9, 1907, 56-9. Sphinx-Oedipe,
Nancy, 1906-7, 39-41. Tablettes des Cotes, Gauthier-Villars, Paris, 1906. Assoc,
frang. avanc. sc, 36, 1907, II, 32-42; 41, 1912, 38-43.

"Comptes Rendus Paris, 151, 1905, 78. Bull. Amer. Math. Soc, 13, 1906-7, 74. L'enseignement
math., 9, 1907, 185. Bull. Soc. PhUomathique de Paris, (9), 8, 1906, 168, 270; (9), 10,
1908, 4-9, 66-83; (10), 2, 1910, 171-7. Assoc, frang. avanc. sc, 36, 1907, II, 11-20,
49-55; 37, 1909, 33-6; 41, 1912, 44-53; 43, 1914, 29-35. Rend. Accad. Lincei, Rome, (5),
15, 1906, I, 439; 26, 1917, I, 401-5. Sphinx-Oedipe, 1908-9, 81, 97. BuU. Sc. Math.
El6m., 12, 1907, 292-3. II Pitagora, Palermo, 13, 1906-7, 81-91 (table serving to factor
numbers from 30030 to 510 510). Table de caract6ristiques relatives a le base 2310 des
facteurs premiers d'un nombre inf^rieur k 30030, Paris, 1906, 32 pp. Comptes Rendus
Paris, 159, 1914, 597-9; 160, 1915, 758-760; 162, 1916, 346-8; 163, 1916,259-261; 164,
1917, 482-4.

*8Jomal de sciencias math., phys. e nat., acad. sc. Lisbona, (2), 7, 1906, 209-218.

89Bull. Soc. Philomathique de Paris, (9), 9, 1907, 112-128; 10, 1908, 10-41.

s'^Assoc. frang., 41, 1912, 32-7.

soAnnals of Math., (2), 10, 1908-9, 88-104. ^Ubid., pp. 105-115.

s^Factor table for the first ten milhons, Carnegie Inst. Wash. Pub. No. 105, 1909.

'^''Quar. Jour. Math., 41, 1910, 160-7; I'interm^diaire des math., 11, 1904, 65; Math. Quest,
Educ. Times, (2), 7, 1905, 81-5.

"bSphinx-Oedipe, 6, 1911, 187-8; Problem of Lionnet, Nouv. Ann. Math., (3), 2, 1883, 310.

'^'^Math. Quest. Educ. Times, (2), 21, 1912, 82-3.

356 History of the Theory of Numbers. [Chap, xni

E. Lebon'' stated that he constructed in 1911 a table of residues p, p'
permitting the rapid factorization of numbers to 100 million, the manuscript
being in the Bibliotheque de I'lnstitut.

H. W. Stager^ gave theorems on numbers which contain no factors of
the form p{kp-\-l), where k>0 and p is a prime, and listed all such numbers
< 12230.

Lehmer'^ listed the primes to ten million.

A. G^rardin^^ discussed the finding of all primes between assigned limits
by use of stencils for 3, 5, 7, 11,. . .. He^^ described his manuscript of
an auxiliary table permitting the factoring of numbers to 200 million. He^^"
gave a five-page table serving to factor numbers of the second million. Cor-
responding to each prime M^ 14867 is an entr\' P such that A^ = 1 000 000+P
is diWsible by M. If a value of P is not in the table, A^ is prime (the P's
range up to 28719 and are not in their natural order). By a simple division
one obtains the least odd number in any million which is divisible by the
given prime M^ 14867.

C. Boulogne^^ made use of lists of residues modulis 30 and 300.

H. E. Hansen^^ gave an impracticable method of forming a table of
primes based on the fact that all composite numbers prime to 6 are products
of two numbers 6x± 1, while such a product is QN=^ 1, where N = 6xy='X+y
or Qxy—x — y. A table of values of these A^'s up to k serves to find the com-
posite numbers up to 6A-. To apply this method to factor 6N=^ 1, seek an
expression for A^ in one of the above three forms.

N. AUiston^°° described a sieve (a modification of that by Eratosthenes)
to determine the primes 4n+l and the primes An — l.

H. W. Stager^"^ expressed each number < 12000 as a product of powers
of primes, and for each odd prime factor gave the values >0 of A: for all
divisors of the form p{kp-{-l). The table thus gives a list of numbers which
include the numbers of Sylow subgroups of a group of order ^ 12000.

In Ch. XVI are cited the tables of factors of a^+1 by Euler,^' Escott,^^
Cunningham^^ and WoodalP; those of a--\-k- (^* = 1, . . . , 9) of Gauss"; those
of ?/" + l, 2/^±2, y'=t. 1, x^zti/^, 2«=tg, etc., of Cunningham.^^- ^"^ Concern-
ing the sieve of Eratosthenes, see No\'iomagus-^ of Ch..I, Poretzkj^^ of Ch.
V, :MerUn"^ and de Polignac^*^"-^ of Ch. XVIII. Saint-Loup" of Ch. XI,
Re>Tnond^^^ and Kempner^^^ of Ch. XIV, represented graphically the divi-
sors of numbers, while Kulik^^ gave a graphical determination of primes.

»»L'interin6diaire des math., 19, 1912, 237.

•♦University of California Public, in Math., 1, 1912, No. 1, 1-26.

•*LiHt of prime numbers from 1 to 10,006,721. Carnegie Inst. Wash. Pub. No. 165, 1914. The
introduction gives data on the distribution of primes.

"Math. Gazette, 7, 1913-4, 192-3.

•'Assoc, frang. avanc. sc, 42, 1913, 2-8; 43, 1914, 26-8.

»«/bw/., 43, 1914, 17-26.

••"^Sphinx-Oedipe, s^rie sp4ciale. No. 1, Dec, 1913.

••L'enseignement math., 17, 1915, 93-9. Cf. pp. 244-5 for remarks by G^rardin.
"""Math. Quest. Educat. Times, 28, 1915, 53.

'"A Sylow factor table of the first twelve thousand numbers. Carnegie Inst. Wash. Pub. No.
151, 1916.

CHAPTER XIV.

METHODS OF FACTORING.
Factoring by Method of Difference of Two Squares.

Fermat^ described his method as follows: "An odd number not a square
can be expressed as the difference of two squares in as many ways as it
is the product of two factors, and if the squares are relatively prime the
factors are. But if the squares have a common divisor d, the given number
is divisible by d and the factors by Vrf- Given a number n, for example
2027651281, to find if it be prime or composite and the factors in the latter
case. Extract the square root of n. I get r = 45029, with the remainder
40440. Subtracting the latter from 2r+l, I get 49619, which is not a
square in view of the ending 19. Hence I add 90061 = 2+2r+l to it.
Since the sum 139680 is not a square, as seen by the final digits, I again
add to it the same number increased by 2, i. e., 90063, and I continue until
the sum becomes a square. This does not happen until we reach 1040400,
the square of 1020. For by an inspection of the sums mentioned it is easy
to see that the final one is the only square (by their endings except for
499944). To find the factors of n, I subtract the first number added,
90061, from the last, 90081. To half the difference add 2. There results
12. The sum of 12 and the root r is 45041. Adding and subtracting the
root 1020 of the final sum 1040400, we get 46061 and 44021, which are the
two numbers nearest to r whose product is n. They are the only factors
since they are primes. Instead of 11 additions, the ordinary method of
factoring would require the division by all the numbers from 7 to 44021."

Under Fermat,^^^ Ch. I, was cited Fermat's factorization of the number
100895598169 proposed to him by Mersenne in 1643.

C. F. Kausler^ would add 1^, 2^, . . . to iV to make the sum a square.

C. F. Kausler^ proceeded as follows to express 4m+l in the form p^ — q^.
Then q is even, q = 2Q. Set p-q = 2^-\-l. Then w = Q(2i3+l)+/3(|8+l).
Subtract from m in turn the pronic numbers i8(/3+l), a table of which he
gave on pp. 232-267, until we reach a difference divisible by 2/3+1.

Ed. Collins,^ in factoring N by expressing it as a difference of two squares,
let g^ be the least odd or even square > A^, according as N= 1 or 3 (mod 4),
and set N = g^ — r. If r is not a square, set r = h^ — c, where h^ is the even
or odd square just >r, according as r is even or odd, whence c = 4d, N = g^ —
h^-\-4:d. By trial find integers x, y such that both g^-\-x and h^-\-y are
squares, while x — y = 4id. Then N will be a difference of two squares.

^Fragment of a letter of about 1643, Bull. Bibl. Storia Sc. Mat., 12, 1879, 715; Oeuvres de Fer-
mat, 2, 1894, 256. At the time of his letter to Mersenne, Dec. 26, 1638, Oeuvres, 2, p. 177,
he had no such method.

"Euler's Algebra, Frankfort, 1796, III, 2. Anhang, 269-283. Cf. Kausler, De Cribro Eratos-
thenis. 1812.

»Nova Acta Acad. Petrop., 14, ad annos 1797-8 (1805), 268-289.

<BuU. Ac. Sc. St. Pdtersbourg, 6, 1840, 84-88.

357

358 History of the Theory of Numbers. Chap, xivi

F. Landr>'* used the method of Ferinat, eliminating certain squares by
their endings and others by the use of moduU.

C. Henry^ stated that Landry's method is merely a perfection of the
method given in the article "nombre premier" in the Dictionnaire des
Math^matiques of de Montferrier. It is improbable that the latter in-
vented the method (based on the fact that an odd prime is a difference
of two squares in a single way), since it was given by Fermat.

F. Thaarup^ gave methods to limit the trials for x in x'^ — y^ = n. We
may multiply n by f = a^ — b^ and investigate nf = X" — Y^, X = ax — by,
Y = bx — ay. We may test small values of y, or apply a mechanical test
based on the last digit of n.

C. J. Busk^ gave a method essentially that by Fermat. It was put
into general algebraic form by W. H. H. Hudson.^ Let N be the given
number, n" the next higher square. Then

N=^n'-ro={n+iy-r,= ...,

where ri, r^,... are formed from ro by successive additions of 2?i + l, 2nH-3,
2n+5, . . .. Thus r^ = ro+27?27i+??r. If r^ is a square, iV is a difference
of two squares. A. Cunningham {ibid., p. 559) discussed the conditions
under w^hich the method is practical, noting that the labor is prohibitive
except in favorable cases such as the examples chosen by Busk.

J. D. Warner^*" would make N = A~—B'^ by use of the final two digits.

A. Cunningham^^ gave the 22 sets of last two digits of perfect squares, as
an aid to expressing a number as a difference of two squares, and described
the method of Busk, which is facilitated by a table of squares.

F. W. Lawrence^ ^ extended the method of Busk (practical only when
the given odd number iV is a product of two nearly equal factors) to the
case in which the ratio of the factors is approximately l/m, where I and m
are small integers. If I and ??? are both odd, subtract from bnN in turn the
squares of a, a+1, . . . , where o^ just exceeds ImN, and see if any remainder
is a perfect square (6") . If so, ImN = (a+ T)'^ — 6^.

G. Wertheim^^ expressed in general form Fermat's method to factor
an odd number ?n. Let a^ be the largest square <m and set m = a~+r.
If p=2a+l— r is a square (n^), we eliminate r and get m = {a-{-l-\-n)
X (a+1 — n). If p is not a square, add to p enough terms of the arithmetic
progression 2a +3, 2a+5, . . . to give a square:

p+(2a+3)-}-...H-(2a+2n-l)=s".

'Aux math^maticiens de toutes les parties du monde: communication sur la decomposition des
nombres en leurs facteurs simples, Paris, 1867. Letter from Landry to C. Henry, Bull.
Bibl. Storia Sc. Mat.. 13, 1880, 469-70.

•Assoc, frang. av. sc, 1880, 201; Oeuvres de Fermat, 4, 1912, 208; Sphinx-Oedipe, 4, 1909, 3«
Trimestre, 17-22. ^Tidsskrift for Mat., (4), 5, 1881, 77-85.

•Nature, 39, 1889, 413-5. 'Nature, 39, 1889, p. 510.

»'Proc. Amer. Assoc. Adv. Sc, 39, 1890, 54r-7.

"Mess. Math., 20, 1890-1, 37-45. Cf. Meissner.i" 137-8.

"/Wd., 24, 1894-5, 100.

»»Zeit8chrift Math. Naturw. Unterricht, 27, 1896, 256-7.

Chap. XIV] METHODS OF FACTORING. 359

Then 2an+n^-r = s^ and m = {a-\-ny-s^. The method is the more rapid
the smaller the difference of the two factors.

M. Neumann^^ proved that this process of adding terms leads finally
to a square and hence to factors, one of which may be 1.

F. W. Lawrence^^ denoted the sum of the two factors of n by 2a and the
difference by 2b, whence n = a^ — 6^. Let q be the remainder obtained by
dividing n by a chosen prime p, and write down the pairs of numbers < p
such that the product of two of a pair is congruent to q modulo p. If
p = 7, q = S, the pairs are 1 and 3, 2 and 5, 4 and 6, whence 2a=4, 0 or 3
(mod 7). Using various primes p and their powers, we get limitations on
a which together determine a. The work may be done with stencils. The
method was used by Lawrence^^ to show that five large numbers are primes,
including 10, 11 and 12 place factors of 3^^ — 1, 10^^ — 1, 10^^ — 1, respectively.
The same examples were treated by other methods by D. Biddle.^^

A. Cunningham^'^ remarked that in computing by Busk's method a
k for which {s+ky—N is a, square, we may use the method of Lawrence,
just described, to limit greatly the number of possible forms of k.

F. J. Vaes^^ expressed N in the form a^ — b"^ by use of the square a^ just
>A^ and then increasing a by 1, 2, ... , and gave (pp. 501-8) an abbreviation
of the method. He strongly recommended the method of remainders
(p . 425) : If p is a factor oiG = h^ — g^, and iig={G — l)/2 has the remainder
r when divided by p, then h={G+l)/2 must have the remainder r+1,
so that p is a factor of 2r-\-l=G. For example, let G = 80047, whence

^ = 200H23 = 20M99+24 = 202-198+27,....

For r = 24, 27, 32, . . . we see that 2r+l is not a multiple of 201, 202, . . .
until we reach gr = 209-191 +p, p=104, 2p+ 1 = 209. Thus 209 divides G.

P. F. Teilhet^^ wrote N = a^-b in the form (a+kY-P, where P = k^
-{-2ak-{-b. Give to k successive values 1, 2, . . . (by additions to P), until
P becomes a square v^. To abbreviate consider the residues of P for small
prime moduli.

E. Lebon^° proceeded as had Teilhet^^ and then set /=a+A; — y. Then

2kf={a-fy-b,

and we examine primes /< a to see if k is an integer.

M. Kraitchik^^ would express a given odd number A in the form
if—x^ by use of various moduli p. Let A = r (mod p) and let Oi, . . . , a„ be the

"Zeitschrift Math. Naturw. Unfcerricht, 27, 1896, 493-5; 28, 1897, 248-251.

"Quar. Jour. Math., 28, 1896, 285-311. French transl., Sphinx-Oedipe, 5, 1910, 98-121, with

an addition by Lawrence on g^ +1.
isProc. Lond. Math. Soc, 28, 1897, 465-475. French transl., Sphinx-Oedipe, 5, 1910, 130-6.
i^Math. Quest. Educat. Times, 71, 1899, 113-4; cf. 93-99.
"/bid., 69, 1898, 111.
i«Proc. Sect. Sciences Akad. Wetenschappen Amsterdam, 4, 1902, 326-336, 425-436, 501-8

(EngUsh); Verslagen Ak. Wet., 10, 1901-2, 374-384, 474-486, 623-631 (Dutch).
i^L'intermediaire des math., 12, 1905, 201-2. Cf. Sphinx-Oedipe, 1906-7, 49-50, 55.
"Assoc, franc, av. sc, 40, 1911, 8-9.
^^Sphinx-Oedipe, Nancy, Mai, 1911, num^ro special, pp. 10-16.

360 History of the Theory of Numbers. [Chap, xiv

quadratic residues of p. Then r-\-x'^=ai (mod p). Thus a, — r must be
a quadratic residue. Reject from Oi, . . . , a^ the terms for which a^ — r is not
in the set. We get the possible residues of x modulo p. His method to fac-
tor 0"=*= 1 is the same as Dickson's^^^ and is applied to show that the factor
(273_|_237 4-i)/(5.239-9929) of 2"^+l is a prime in case it has no factor
between 10500 and 108000.

Kraitchik" extended the method of Lawrence.

F. J. Vaes^^ applied his^^ method to factor Mersenne's^ number. The
same was factored by various methods in L'lnterm^diaire des Math6mat-
iciens, 19, 1912, 32-5. J. Petersen, ibid., 5, 1898, 214, noted that its product
by 8 equals k^+k, where A: = 898423.

Method of Factoring by Sum of Two Squares.

Frenicle de Bessy^^ proposed to Fermat that he factor h given that

h = a^+b''-=c'+(f, as 221 = 100+121 = 196+25.

In 1647, Mersenne^^ (of Ch. I) noted that a number is composite if it be
a sum of two squares in two ways.

L. Euler^^ noted that iV is a prime if it is expressible as a sum of two
squares in a single way, while if iV = a^+5^ = c^+d^, N is composite :

{{a-cY+{h-d)'} {{a+cy+ih-d)']
4(6 -d)2

Euler^' proved, that, if a number A'" = 4n+1 is expressible as the sum of
two relatively prime squares in a single way, it is a prime. For, if iV were
composite, then N={d^-{-b^){c^+d^) is the sum of the squares of ac^bd and
ad=f^bc, contrary to hypothesis. If iV = a^+6^ = c^+d^, N is composite;
for if w^e set a = c-\-x, d = b-\-y, and assume* that the common value of
2cx-\-x^ and 2by-\-'if' is of the form xyz, we get

2c = yz-x, 2b = xz-y, N = b'^+c^+xyz = \{x'^-]-y^){l+z^),

whence x^-\-y^ or {x^+y^)/4: is a factor of N. To express iV as a sum of two
squares in all possible ways, use is made of the final digit of N to limit the
squares x^ to be subtracted in seeking differences N — x^ which are squares.
Several numerical examples of factoring are treated in full.

Euler-^ gave abbreviations of the work of applying the preceding test.
For example, if 4n+l=5m+2 = x^+!/^, then x and y are of the form

"Sphinx-Oedipe, 1912, 61-4.

i^L'enseigncment math., 15, 1913, 333-4.

"Oeuvres de Fermat, 2. 1894, 232, Aug. 2, 1641.

"Letters to Goldbach, Feb. 16, 1745, May 6, 1747; Corresp. Math. Phys. (ed., Fuss), I, 1843,
313, 416-9.

"Novi Comm. Ac. Petrop., 4, 1752-3, p. 3; Comm. Arith., 1, 1849, 165-173.

*Euler gave a faultless proof in the margin of his posthimious paper, Tractatus, §570, Comm.
Arith., 2, 573; Opera postuma, I, 1862, 73. We have {a+c)ia-c) = {b+d){d-b) =pqrs,
a+c = pq,a—c = rs, b+d = pr, d—b = qs [since, if pbe theg. c. d. of a+c, b+d, then g(a—c)
is divisible by r, whence a—c = rs]. Hence a2+6^ = (p*+a^)(g'+r')/4.

»»Novi Comm. Ac. Petrop., 13, 1768, 67; Comm. Arith., 1, 379.

Chap. XIV] METHODS OF FaCTOKING. 361

5p± 1. To express a number as x^+y^, subtract squares in turn and seek a
remainder which is a square.

N. Beguehn^^ proposed to find x such that 4pV+ 1 is a prime by exclud-
ing the values x making the sum composite. The latter is the case if

4pV+l=462+(2c+l)2, a;2 = ^!±^.

Set X = q+b/p. Then b is expressed rationally in terms of c and the known
p. Taking p = l, he derived a tentative process for finding a prime, of the
form 4x^+1, which exceeds a given number a.

L. Euler^° proved that 1000^+3^ is prime since not expressible as a sum of
two squares another way.

A. M. Legendre^"" factored numbers represented as a sum of two squares
in two ways.

J. P. Kulik's^"^ tables VIII and IX, relating to the ending of squares,
serve to test if 4n+l is a sum of two squares and hence to test if it be prime
or composite.

Th. Harmuth^^ suggested testing a^-j-b^ for factors, where a and b are
relatively prime, by noting that it is divisible by 5 if a= =t 1, 6= ± 2 (mod 5) ,
and similar facts for p = 13, 17, 29, 37, there being p — 1 sets of values of a, b
for each prime p = 4n+l.

G. Wertheim^^ explained in full Euler's^'' method of factoring.

R. W. D. Christie and A. Cunningham^^ granted N = A^+B^ = C^+D'^
and showed how to find a,...,dso that N={a^+b^){c^-\-cP). Similarly, if
N = x^-\-Py'^ in two ways.

Factoring by Use of Binary Quadratic Forms.

L. Euler^^ noted that a number is composite if it be expressible in two v^ /* .fi'*^
ways in the form/ = ax^+i(32/^. The product of two numbers of the form/
is of the form g = aPx^+y^; the product of a number of the form / by one of
the form g is of the form /. If for m>2 a composite number mp is express-
ible in a single way in the form /, there exist an infinitude of composite
numbers mq expressible in a single way by /. He called (§34) a number
A'' idoneal (numerus idoneus) if, for a^ = N, every number representable
hy f = ax^+^y^ (with ax relatively prime to ^y) is a prime, the square of a
prime, the double of a prime or a power of 2, so that a number representable
by / in a single way is a prime. It suffices to test N+y^<4N, y prime to N.
He gave (§39, p. 208) the 65 idoneal numbers 1, 2, . . ., 1848 less than 10000.

"Nouv. M^m. Acad. Sc. BerUn, 1777, ann6e 1775, 300.

soNova Acta Petrop., 10, 1792 (1778), 63; Comm. Arith., 2, 243-8.

^'^Theorie des nombres, ed. 3, i830, I, 310. Simplification by Vuibert, Jour, de math. 6\em.,

10, p. 42. Cf. I'interm^diaire des math., 1, 1894, 167, 245; 18, 1911, 256.
3obTafebi der Quadrat und Kubik Zahlen ... bis hundert Tausend, Leipzig, 1848.
"Archiv Math. Phys., 67, 1882, 215-9.
32Elemente der Zahlentheorie, 1887, 295-9.
"Math. Quest. Educat. Times, (2), 11, 1907, 52-3, 65-7, 89-90.
"Nova Acta Petrop., 13, 1795-6 (1778), 14; Comm. Arith., 2, 198-214.

362 History of the Theory of Numbers. [Chap, xiv

Euler^* used the idoneal number 232 to find all values of a < 300 for
which 232a- + 1 is a prime, by excluding the values of a for which 232a^-hl
= 232x~-\-y-,y>l.

Euler^^ noted that N = a~ -\-\b- = x^ +\y^ imply

N = l(\nr+n'^){\p^-\-q^), a=^x = \mp, nq; y=^h = mq, np,

so that Xp^ + g-, or its half or quarter, is a factor of A''. He gave (p. 227)
his^' former table of 65 idoneal numbers. Given one representation by
cur 4-/3?/", where a/3 is idoneal, he sought a second representation. If
A^ = 4n + 2 is idoneal, 4iV is idoneal.

Euler^*^ called mx--\-ny- a congruent form if everj' number representable
by it in a single way (with x, y relatively prime) is a prime, the square of a
prime, the double of a prime, a power of 2, or the product of a prime by a
factor of vin. Then also vinx~-\-y~ is a congruent form and conversely.
The product mn is called an idoneal or congruent number. His table of 65
idoneal numbers is reproduced (§18, p. 253). He stated rules for deducing
idoneal numbers from given idoneal numbers. He factored numbers
expressed in two ways by ax^+/3i/-, where a/S is idoneal, and noted that a
composite number may be expressible in a single way in that form if a^ is
not idoneal.

Euler^^ proved that the first five squares are the only square idoneal
numbers.

C. F. Kausler^- proved Euler's theorem that a prime can be expressed in
a single way in the form mx'^-\-ny'^ ii m, n are relatively prime. To find a
prime v exceeding a given number, see whether 38a:- +5?/^ = v has a single set
of positive solutions x, y; or use 1848x"+?/^. As the labor is smaller the
larger the idoneal number 38-5 or 1848, it is an interesting question if there
be idoneal numbers not in Euler's list of 65. Cf. Cunningham. ^^

Euler"*^ gave the 65 idoneal numbers n (with 44 a misprint for 45) such
that a number representable in a single way by nx~-\-y'^ {x, y relatively
prime) is a prime. By using n = 1848, he found primes exceeding 10 million.

N. Fuss^ stated the principles due to Euler.^^

E. Waring^^ stated that a number is a prime if it be expressible in a single
way in the form ar-\-mh^ and conversely.

A. M. Legendre"*^ would express the number A to be factored, or one of
its multiples kA , in the form t~+air, where a is as small as possible and within
the limits of his Tables III-YII of the linear forms of divisors of f^au^.

»»Nova Acta Petrop., 14, 1797-8 (1778). 3; Ck)mm. Arith., 2, 215-9.

»»/Wd., p. 11; Comm. Arith., 2, 220-242. For X = 2, Opera postuma, I, 1862, 159.

"/Wd.. 12, 1794 (1778), 22; Comm. Arith., 2, 249-260.

"/6wf., 15, ad annos 1799-1802 (1778), 29; Comm. Arith., 2, 261-2.

"Ibid., 156-180.

"Nouv. M^m. Berlin, ann6e 1776, 1779, 337; letter to Beguelin, May, 1778; Comm. Arith., 2,

270-1.
**Ibid., 340-6

«Medit. Algebr., ed. 3, 1782, 352.
«^h6orie des nombres, 1798, pp. 313-320; ed. 2, 1808, pp. 287-292. German transl. by Maser,

1, 329-336. Cf. Sphinx-Oedipe, 1906-7, 51.

Chap. XIV] METHODS OF FACTORING. 363

Then the divisors of A are included among these linear forms. When
VS is converted into a continued fraction, let (VM +/)/!) be a complete
quotient, and p/q the corresponding convergent. Then ^D = p^ — kAq^,
so that the divisors of A are divisors oi p^=f=D.

C. F. Gauss'*^ stated that the 65 idoneal numbers n of Euler and no
other numbers have the two properties that all classes of quadratic forms
of determinant —n are ambiguous and that any two forms in the same
genus (Geschlecht) are both properly and improperly equivalent.

Gauss^^ gave a method of factoring a number M based on the deter-
mination of various small quadratic residues of M.

Gauss^^ gave a second method of factoring M based on the finding of
representations of M by forms x^+D, where D is idoneal.

F. Minding^° gave an exposition of the method of Legendre.^^

P. L. Tchebychef^^ gave a rapid process to find many forms x^^ay^
which represent a given number A or a multiple of A. Then a table of
the linear forms of the divisors of x^^ay^ serves to limit the possible factors
of A.

Tchebychef^^ gave theorems on the limits between which lie at least
one set of integral solutions of x^ — Dy^ = ± iV. If there are two sets of solu-
tions within the limits, N is composite. There are given various tests for
primality by use of quadratic forms.

C. F. Gauss^^ left posthumous tables to facilitate factoring by use of
his*^ second method.

F. Grube^^ criticized and completed certain of Euler's proofs relating to
idoneal numbers, here called Euler numbers. While Gauss^^ said it is easy
to prove Euler's*^ criterion for idoneal numbers, Grube could prove only
the following modification: Let Q, be the set of numbers D+n^^4Z) in
which n is prime to D. According as all or not all numbers of 12 are of the
form q, 2q, q"^, 2^ {q a prime), D is or is not an idoneal number.

E. Lucas^^ proved that if p is a prime and A; is a positive integer, and
p = x^+ky^, then pT^Xi^+ky^^ for values Xi, yi distinct from ^x, ^y.

P. Seelhoff^^ made use of 170 determinants (including the 65 idoneal
numbers of Euler and certain others of Legendre), such that every reduced
form in the principal genus is of the type ax^-\-by^. To factor A^ seek
among the numbers m of which iV is a quadratic residue several values

<^Disq. Arith., 1801, Art. 303.

"7btd., Arts. 329-332.

*mid., Arts. 333-4.

s^Anfangsgriinde der Hoheren Arith., 1832, 185-7.

"Theorie der Congruenzen (in Russian), 1849; German transl. by H. Schapira, 1889, Ch. 8,

pp. 281-292.
"Jour, de Math., 16, 1851, 257-282; Oeuvres, 1, 73.
«Werke, 2, 1863, 508-9.
"Zeitschrift Math. Phys., 19, 1874, 492-519.
"Nouv. Corresp. Math., 4, 1878, 36. [Euler."]
"Archiv Math Phys., (2), 2, 1885, 329; (2), 3, 1886, 325; Zeitschrift Math. Phys., 31, 1886, 166,

174, 306; Amer. Jour. Math., 7, 1885, 264; 8, 1886, 26-44.

364 History of the Theory of Numbers. [Chap, xiv

for which N is represent able by x^-\-my-. For example, if iV = 31-2^*-f 1,

Eliminating 19-83 between the first two, we get nN = w'^ — 7f. This with
the third leads to factors of N. In general, when elimination of common
factors of the 77i's has led to representations of two multiples of N by the
same form x~+ny^, we may factor N unless it be prime.

H. Weber^^ computed the class invariants for the 65 determinants of
Euler and remarked that there is no known proof of the fact found by
induction by Euler and Gauss that there are only 65 determinants such that
all classes belonging to the determinant are ambiguous and hence each
genus has only one class.

T. Pepin^^ developed the theory of Gauss'^^ posthumous tables and the
means of deducing complete tables from the given abridged tables. Pepin^*
showed how to abridge the calculations in using the auxiliary tables of Gauss
in factoring a" — 1, where a and n are primes.

D. F. Seliwanoff^° noted that the factoring of numbers of the form
t' — Du- reduces to the solution of {D/x) = \, all solutions of which are
easily found by use of six relations by Euler on these Jacobi symbols {D/x) .

E. Lucas" gave a clear proof of Euler's remark that a prime can not be
expressed in two ways in the form Ax~-\-By-, if A, B are positive integers.

S. Levanen^^ showed and illustrated by examples and tables how binary
quadratic forms may be applied to factoring.

G. B. ^Mathews*"^ gave an exposition of the subject.

T. Pepin^ applied determinants — 8n — 3 for which each genus has three
classes of quadratic forms. The paper is devoted mainly to the solution
of X-+ (871+3)?/"" = 4A, where A is the number to be factored.

T. Pepin^^ assumed that the given number N had been tested and found
to have no prime factor ^p. Let Xx+1, Xy+1 be the two factors of N,
each between p and N/p. The sum of the factors lies between 2VW and
p+N/p. Let x—y = u, x+y=pz. Then {N — l)/\ = Xxy+x+y gives

in which special values are assigned to p. This equation yields a quadratic
congruence for w" with respect to an arbitrary prime modulus, used as an
excludant. The method applies mainly to numbers a^=^l.
E. Cahen^^ used the linear divisors of x^ + Dy'^.

'"Math. Annalen, 33, 1889. 390-410.

"Atti Accad. Pont. Nuovi Lincei, 48, 1889, 135-156.

"Ibid., 49, 1890. 163-191.

"Moscow Math. Soc, 15, 1891, 789; St. Petersburg Math. See, 12, 1899.

•'Th6orie des nombres, 1891, 356-7.

"^vereigt af finska Vetenskaps-Soc. forhandlingar, 34, 1892, 334-376.

"Theory of Numbers, 1892, 261-271. French transl., Sphinx-Oedipe, 1907-8, 155-8, 161-70.

"Memorie Accad. Pontif. Nuovi Lincei, 9, I, 1893, 46-76. Cf. Pepin," 332.

«;6iV/., 17, 1900-1, 321-344; Atti, 54, 1901, 89-93. Cf. Meissner"*, 121-2.

"filaments de la th^orie des nombres, 1900, 324-7. Sphinx-Oedipe, 1907-8, 149-155.

Chap. XIV] METHODS OF FACTORING. 365

A. Cunningham" and J. Cullen listed the 188 prime numbers x^+18482/^
between 10"^ and 101-10^, with x prime to 1848?/.

A. Cunningham^ ^ noted that two representations of N by ixx^-\-vy^
lead to factors of N under certain conditions.

A. Cunningham^^ recalled that an idoneal number / has the property
that, if an odd number A'' is expressible in only one way in the form
N = mx^-\-ny^, where mn = I, and mx^ is prime to ny^, then A" is a prime or
the square of a prime. Euler's largest I is 1848. There is no larger I under
50000, a computation checked by J. Cullen. Cunningham noted on the
proof-sheets of this history that this limit has been extended to 100 000.

A. Cunningham^" noted conditions that an odd prime be expressible by
f^qu" when q or —q'l^ idoneal.

F. N. Cole'^^ discussed Seelhoff's^^ method of factoring.

Al. Laparewicz^^ described and applied Gauss' ^^'^^ two methods.

P. Meyer^^ discussed Euler's theorem that, if n is idoneal, a number
representable only once by x^-\-ny'^ is a prime.

R. BurgwedeF^ gave an exposition and completion of the method of
Euler^^'^^ and an exposition of the methods of Gauss.^^'*^

L. Valroff stated and A. Cunningham'^^" proved that (Dx'^ — a^) (Dy"^ — a^)
= Dz^ — a^ implies that one factor is composite unless x^ = y^ = 4: when
o = 1, D = 2, and in the remaining cases if the two factors are distinct and > 1.

A. Gerardin'^^ gave a method illustrated for N = a^ — 5-29^, where a = 6326.
We shall have a second such representation N = (a-{-5xy — 5y^ if

E=5x^+2ax+841=y^.

Use is made of various moduli ?« = 4, 3, 7, 25, ... . On square-ruled paper,
mark x = 0, 1, 2, . . . at the head of the columns. On the line for modulus m,
shade the square under the heading x when x makes E a quadratic non-
residue of m. Then examine the column in which occurs no shaded square.
Up to x^l5, these are x = 0 (excluded), and x = 4, which gives A = 6346^
— 5-227^ and the factor 99^ — 5-2^. The same diagram serves for all num-
bers 1050 ff +671, our N being given by i7 = 38108. To apply the method
to A = (2a;)*+1 = (4x^+1)^ — 2(2x)^, seek a second representation N=(4x^
+2p + lY-2{2uy. The condition is {2p-\-l)x^+Mp-j-l)=u^, solutions
of which are found for p = 1, 8, 9, . . . , 6^, 35^, ... Or we may choose x, say
X = 48, and find p = S, u = 198.

s^Brit. Assoc. Reports, 1901, 552. The entry 10098201 is erroneous.

"Proc. London Math. Soc, 33, 1900-1, 361.

«976id., 34, 1901-2, 54.

■"^Ibid., (2), 1, 1903, 134.

7iBuU. Amer. Math. Soc, 10, 1903-4, 134-7.

"Prace mat. fiz., Warsaw, 16, 1905, 45-70 (PoUsh).

^'Beweis eines von Euler entdeckten Satzes, betreffend die Bestimmung von Primzahlen, Diss.,

Strassburg, 1906.
'^Ueber die Eulerschen und Gausschen Methoden der Primzahlbestimnaung, Diss., Strassburg,

1910, 101 pp.
'*»Sphinx-Oedipe, 7, 1912, 60, 77-9.
"Wiskundig Tijdschrift, 10, 1913, 52-62.

366 History of the Theory of Numbers. [Chap, xiv

G^rardin^® gave a note on his machine to factor large numbers, espe-
cially those of the form 2x^ — 1.

Factoring by Method of Final Digits.

Johann Tessanek^° gave a tedious method of factoring N, not divisible
by 2, 3, or 5, when A^/10 is within the limits of a factor table. For example,
let N=10a+l; its factors end in 1,1 or 3,7 or 9,9. To treat one of the
four cases, consider a factor lOx+3, the quotient being 102+7. Then z is
the quotient of a — 2 — 7x by lOx+3. Give to x the values 1, 2, . . ., and test
a — 9 for the factor 13, a — 16 for 23, etc., by the factor table. He gave a
lengthy extension^^ to di\'isors 100j+10/+gr. Again, to factor iV = 2a + l,
given a table extending to N/2, note that if 2xH-l is a divisor of N, it
di\'ides a—x, which falls in the table. F. J. Studnicka^^ quoted the last
result.

N. Beguelin^ would factor iV = 4p+3 by considering the final digit of
TT = (A'' — 1 1)/4 and hence find the proper line in an auxihary table (pp. 291-2) ,
each line containing four fractional expressions. Proceed with each until
we reach a fraction whose numerator is zero. Then its denominator is a
factor of A^.

Georg Simon KliigeP noted that a number, not divisible by 2, 3 or 5,
is of the form 30x+m (m = l, 7, 11, 13, 17, 19, 23, 29). Suppose 10007 =
(30x+w)(30!/+n). Then {m, n) = (l, 17), (7, 11), (13, 29) or (19, 23).
For m = 1, n = 17, we get

333-?/

^=3o^Ti7' ^<^' y<^'

But X is not integral for y = 0, 1, 2, 3.

Johann Andreas von Segner {ibid., 217-225) took two pages to prove
that any number not divisible by 2 or 3 is of the form 6n='= 1 and noted that,
given a table of the least prime factor of each 6n=tl, he could factor any
number within the limits of the table!

Sebastiano Canterzani^^ would factor 10^ + 1, by noting the last digits
1, 1 or 3, 7 or 9, 9 of its factors. If one factor ends in 7, there are 10
possibilities for the digit preceding 7; if one ends in 1 or 9, there are five
cases; hence 20 cases in all. A. Niegemann^^" used the same method.

Anton Niegemann^® gave a method of computing a table of squares
arranged according to the last two digits. Thus, if A76 = {l0x — Qy, then

™\s30c. fran?. avanc. sc, 43, 1914, 26-8. Proc. Fifth Internat. Congress, II, 1913, 572-3;

Brit. Assoc. Reports, 1912-3, 405.
••Abhandl. einer Privatgesellschaft in Bohmen, zur Aufnahme der Math., Geschichte, . . . , Prag, I,

1775, 1-64.
"M. Cantor, Geschichte Math., 4, 1908, 179.
"Casopis, 14, 1885, 120 (Fortschr. der Math., 17, 1885, 125).
"Nouv. Mdm. Ac. Berhn, ann^e 1777 (1779), 265-310.
•*Leipziger Magazin fiir reine u. angewandte Math, (eds., J. Bernoulli und Hindenburg), 1, 1787,

199-216.
"Memorie dell' Istituto Xazionale Italiano, Classe di Fis. e Mat., Bologna, 2, 1810, II, 445-476.
""Entwickelung . . . Theilbarkeit, Jahresber. Kath. Gymn. Kobi., 1847-8, 23.
"Archiv Math. Phys., 45, 1866, 203-216 .

^'11 Chap. XIV] METHODS OF FACTORING. 367

A0 = 10x^ — 12x — 4:, whence 12a:+4 is divisible by 10, so that a: = 5(i — 2.
Then A=25d'^ — 2Qd+Q. Thus if we delete the last two digits 7 , 6 of squares
A7Q, we obtain numbers A whose values for d = l, 2, . . . can be derived
from the initial one 5 by successive additions of 49, 49+50, 49+2-50, . . . .
He gave such results for every pair of possible endings of squares.

A similar method is applied to any composite number. One case is
when the last two digits are m, 1 and Aml = (10a; — 1)(10?/ — 1). Then

A0 = 10xy — y — x — m, y+x+m = 10a, A = 10ax—x'^—mx — a.

The discriminant of the last equation must be a square. A table of values
of A for each a may be formed by successive additions.

G. Speckmann^^ noted that the two factors of AT" = 2047 end in 1 and 7
or 3 and 9. Treating the first case, we see that, if a and b are the digits in
tens place, 6+7a=4 (mod 10), so that the factors end in 01 and 47, or 11 and
77, etc.

G. Speckmann^^ wrote the given number prime to 3 in the form 9a +6
(6<9), so that the sum of its digits is =6 (mod 9). By use of a small
auxiliary table we have the residues modulo 9 of the sums of the digits of
every possible pair of factors.

R. W. D. Christie^^ and D. Biddle^° made an extensive use of terminal
digits.

E. Barbette^ ^ noted that lOd+u has a divisor lOw — 1 if and only if
d+?nw has that divisor. Set d-\-'mu = n(10m — l), d = 10d'+u'. Then
mn = d'-\-x, lOx = 'mu-\-n-\-u'.

Eliminating n, we get a quadratic for m. Its discriminant is a quadratic
function of x which is to be made a square. Similarly for lOm + 1, 10m ±3.

A. Gerardin^^" developed Barbette's^^ method.

R. Rawson^^ found Fermat's^ factors of a number proposed by Mersenne
by writing it to the base 100 and expressing it as (a- 10^ +23) (6 -10^ +3).

J. Deschamps^^ would use the final digits and auxiliary tables.

A. Gerardin®^ would factor N (prime to 2, 3, 5) by use of

iV=120n+i^=(120x+a)(120i/+6),

and a table showing, for each of the 32 values of K< 120, the 16 pairs o, b
(each< 120) such that ab=K (mod 120). He factored Mersenne's number.^

Factoring by Continued Fractions or Fell Equations.
Franz von Schaffgotsch^"" would factor a by solving az^-^l = x^ (having

"Archiv Math. Phys., (2), 12, 1894, 435. ssArchiv. Math. Phys., 14, 1896, 441-3.

"Math. Quest. Educat. Times, 69, 1898, 99-104. Cf. Meissner,"^ 138-9.

'"/feid., 87-88, 112-4; 71, 1899, 93-9; Mess. Math., 28, 1898-9, 120-149, 192 (correction). Cf.

Meissner,"8 137-8. siMathesis, (2), 9, 1899, 241.

"«Sphinx-Oedipe, 1906-7, [1-2, 17, 33], 49-50, 54, 65-7, 77-8, 81-4; 1907-8, 33-5; 5, 1910,

145-7; 6, 1911, 157-8. s^Math. Quest. Educat. Times, 71, 1899, 123-4.

"^BuU. See. Philomathique de Paris, (9), 10, 1908, 10-26.
s'Assoc. frang., 38, 1909, 145-156; Sphinx-Oedipe, Nancy, 1908-9, 129-134, 145-9; 4, 1909,

3« Trimestre, 17-25.
i»»Abh. Bohmischen Gesell. Wiss., Prag, 2, 1786, 140-7.

368 History of the Theory of Numbers. [Chap, xiv

solutions if a is not a square) and testing x" — 1 for a factor in common with a.
Further, U ay-\-l=x'^ does not hold for l<x<a — 1, then a is a power of a
prime and conversely [false if a = 10].

Marcker^*'^ noted that if there are 2n terms in the period of

and Q = 0, Q' = a, Q" = a'P' -Q',. . .,^

p_i p/_^~Q'' ptf _^~Q"^

r — 1, r — p ' pf ) • ■ • i

then the nth P or its half is a factor of A. If A is a prime, then the nth
Pis 2.

J. G. Birch^°- derived a factor of N from a solution x of x'^ = Ny+l. The
continued fraction for x/{N —x) is of the form

1 J_ J_ ill

Go- 1 +01+02+ ■ • • +a2+ai+ao'
and N is the continuant defined as the determinant with Oq, Oi,. . ., a„_i,
On) On-i>- •■> Oi, Oo in the main diagonal, elements +1 just above this
diagonal, elements —1 just below, and zeros elsewhere. Then the continu-
ant with the diagonal ao> • • •> o„_i is a factor of N.

W. W. R. BalP°^ appHed this method to a number of Mersenne.^

A. Cunningham^*^ noted that a set of solutions of if—Dx^ = — 1 gives at
sight factors of 7/" + l.

M. V. Thielmann^o^ illustrated his method by factoring /c = 36343817.
The partial denominators in the continued fraction for \/^ are 1, 1, 2, 1, 1,
12056. Drop the last term and pass to the ordinary fraction 7/12. Hence
set (12x+7)^ = 12^i/+l. The least solution is x = 4, y = 2\. Using the part
of the period preceding the middle term it» = 2, we get

Y^ = -^, P = l, M = 2, Q = iyM+2P = 6, u = MQ = \2.

Hence ^" — 21m^ = 1 has the solution < = 55. For a suitably chosen n,

ifc = wV+2^n+21= (2g2n+^^ Uu^n+^-^X

where q is the largest integer ^ Q/2. Here n = 502 and the factors of k are
2-3"n + 7 and 2-22n+3.

D. N. Lehmer^''^ noted that if jR = pg' is a product of two odd factors
whose difference is <2y/R, so that Kp— 9)^<V7^, then

x'-Rf = \{V-q?
has the integral solutions x = (p+g')/2, y = \. Hence i(p — g')^ is a denomi-
nator of a complete quotient in the expansion of y/R, as a continued fraction,

""Jour, fur Math., 20, 1840, 355-9. Cf. I'interm6diaire dea math., 20, 1913, 27-8.
J^Mcsa. Math., 22, 1892-3. 52-5.

'o'/6id., p. 82-3. French transl., with Birch"^, Sphinx-Oedipe, 1913, 86-9.
>"/6id., 35, 1905-6, 166-185; abat. in Proc. London Math. Soc. 3, 1905, xxii.
'""Math. Annalen, 62, 1906, 401.

Bull. Amer. Math. Soc, 13, 1906-7, 501-2. French transl., Sphinx-Oedipe, 6, 1911, 138-9.

IM

Chap. XIV]

Methods of Factoring.

369

in view of the theorem of Lagrange: If x^—Ry'^=^D has relatively prime
integral solutions x, y, where D< \/r, then D is a denominator of a com-
plete quotient in the expansion of \/r as a continued fraction.

Factoring by use of Various Moduli.

C. F. Gauss^^° gave a "method of exclusion," based on the use of various
small moduli, to express a given number in a given form mx^+ny^.

V. Bouniakowsky^^^ noted that information as to the prime factors of a
number N may be obtained by comparing the solution x = (l){N) of 2''=1
(mod N) with the least positive solution x = a found by a direct process such
as the following : Since 2" = NK+l, multiply the given N by the unknown
K, each expressed in the binary scale (base 2), add 1 and equate the result to
10. . .0. The digits of K are found seriatim and very simply.

H. J. WoodalP^^ expressed the number N to be factored in the form
^a_|_^6_^ . . . +r, where r< 1000, while a, /3, . . . are small, but not necessarily
distinct. Hence the residues of N with respect to various moduli are
readily found by tables of residues.

F. Landry^^^ employed the method of exclusion by small moduli.

D. Biddle^^^ investigated factors 2Ap + l by using moduli A^, 4A^.

C. E. Bickmore, A. Cunningham and J. CuUen^^^ each treated the large
factor of 10^^+1 by use of various moduli, and proved it is prime.

J. Cullen"^" gave an effective graphical process to factor numbers by
the use of various moduli; the numbers to be searched for in a diagram
are all small.

Alfred Johnsen^^^ used Rt(p) to denote the numerically least residue of
p modulo t. Then, for every p, t, k,

[Rmf+Ri(p-k')^Rt(p) (modO.
If Hs a factor of the given number p, the left member will be divisible by t.
In practice take k^ to be the nearest square to p, larger or smaller. For
example, let p = 4699, k^ = 4624 = 68^ p-k'' = 75. Then

t

[^.(68)P

Rt(75)

Sum

7
13

37

4
9

36

-2
-3

"i

2
6

37

Thus 37 is the least factor of p.

""DJsq. Arith., 1801, Arts. 323-6.

i"M6m. Ac. Sc. St. P^tersbourg, Math.-Phys., (6), 2, 1841, 447-69. Extract in Bull. Ac. Sc, 6,

p. 97. Cf. Nordlund.i"
"2Math. Quest. Educat. Times, 70, 1899, 68-71; 71, 1899, 124.
"sproc^d^s nouveaux . . . , Paris, 1859. Cf. A. Aubry,"^ pp. 214-7.
i"Mess. Math., 30, 1900-1, 98, 190. Math. Quest. Educat. Times, 74, 1901, 147-152.
"'Math. Quest. Educat. Times, 72 1900, 99-103.
"sa/bid., 73, 1900, 133-5; 75, 1901, 10^4. Proc. London Math. Soc, 34, 1901-2, 323-334;

(2), 2, 1905, 138-141. "'Nyt Tidsskrift for Mat., 15 A, 1904, 109-110.

370 History of the Theory of Numbers. [Chap, xiv

K. P. Nordlund^^^ would use the exponent e to which 2 belongs modulo
iV [Bouniakowsky^^^]. For A^ = 91, e = 12 is not a divisor of iV — 1, so that
A^ is composite, and we expect the factor 13.

L. E. Dickson"^ found the factors of 56'±1, 26'Hl, 34^^-}-l, 52^Hl
by an expeditious method. For example, each factor of

is =l(mod 14). Let 6 = (l + 14A;)(l + 14A'i). Then

A'+;i-i + 14A'A-i=4Ar, /:+A'i = 4+14/1.

Thus h and A-j are the roots of a quadratic whose discriminant Q is of the
second degree in In. By use of various moduli which are powers of small
primes, the form of h is limited step by step, until finally at most a half
dozen values of h remain to be tested directly.

L. E. Dickson^ ^® gave further illustrations of the last method.

J. Schatunovsky^^° reduced to a minimum the number of trials in
Gauss'^^° method of exclusion, taking the simplest case m = \. He gave
theorems on the linear forms of the factors of a"~H-D6^, which lead easily to
all its odd factors when D is an odd prime.

H. C. Pocklington^^^ would use Fermat's theorem to tell whether A" is
prime or composite. Choose an integer x and find the least positive residue
of x^"^ modulo A''; if p^l, A'' is composite. But if it be unity, let p be a
prime factor (preferably the largest) of A^— 1 and contained a times in it.
Find the remainder r when x"* is divided by A', where 7n = (A' — l)/p. If
Tt^I, let 6 be the g. c. d. of r— 1 and A^. If 6>1, we have a factor of A^.
If 6 = 1, all prime factors of A^ are of the form Ap^ + l. But if r = 1, replace
m by mlq^ where q is any prime factor of m and proceed as before.

D. Biddle^^^" made use of various small moduli.

A. Gerardin^^^'' used various moduli to factor 77073877.

See papers 14, 15, 21, 22, 48, 65.

Factoring Into Two Numbers 6n±l.
G. W. Kraft^" ^^^^^ ^hat 6a+l = (6w+l)(6n+l) implies

_ a—m
^~6m + l'
Find which 7?? = 1, 2, 3, . . . makes n an integer.

Ed. BartP^ tested 6-186+5 for a prime factor less than 31, just less
than its square root, by noting that 186, 185, 184, 183, 182 are not divisible
by 5, 11, 17, 23, 29, respectively; while the last of 7, 13, 19 is a factor.

'"Gotcborps Kunpcl. Vetenskaps. Hand!., (4), 1905, VII-VIII, pp. 21-4.

»«Amer. Math. Monthly, 15, 1908, 217-222. "'Quar. Jour. Math., 40, 1909, 40-43.

""Der Grosste GemeinschaftUche Teller von Algebr. Zahlen zweiter Ordnung, Diss. Strassburg,
Leipzig, 1912. >"Proc. Cambridge Phil. Sec, 18, 1914-5, 29-30.

"'"Math. Quest. Educat. Times, (2), 25, 1914, 43-6.
"'"L'enseignement math., 17, 1915, 244-5.
'"Novi Comm. Ac. Petrop., 3, ad annos 1750-1, 117-8.
""Zur Theorie der Primzahlen, Progr. Mies, Pilsen, 1871.

Chap. XIV]

Methods of Factoring.

371

F. Landry ^^^ treated the possible pairs 6n± 1 and 6n'± 1 of factors of N.
Taking for example the case of the upper signs, we have

Set n+n' = 6/i+r.

Qnn'+n-\-n' = — - — = Qq-\-r.
6

Then nn' = q — h, whence

- q—n'(r—n')
h = -

6n' + l

Give to n' values such that 6n'+l is a prime < ViV.

K. P. Nordlund^25 treated Qp-l = {Qm+l){Qn-l) solved for m.
D. Biddle^^^ applied the method to 6n±l.
Hansen,^^ of Ch. XIII, used this method.

Miscellaneous Methods of Factoring.

Matsunaga^^^ wrote the number to be factored in the form r^+R. For
r odd, set r = Bi, Bi — 2 = B2, Bg — 2 = ^3, ... and perform the following
calculations :

R = Q,B,+Au

Ai+K2' = Q2B2+A2,
A2-\-Ks' = Q3Bs+As,

etc., until we reach A„ = 0; then Bn is a factor,
and replace i? by jR + 1 in what precedes.

J. H. Lambert ^^° used periodic decimals [see Lambert,^ Ch. VI].

Jean Bernoulli^^^ gave a method based on that of Lambert (Mem. de
Math. Allemands, vol. 2). Let A=a^+b have the factors a—x and
a+x+y. Then x^ = ay— xy — b. Solve for a:. Thus 2/^+ 4a?/ — 46 must be
a square. Take y = l, 2, . . . and use a table of squares.

J. Gough^^^ gave a method to find the factors r, s of each number f^ — c
between (/— 1)^ and/^. For example, let/=3 and make a double row for
each r = l,. . ., /. In the upper row for r = l, insert 2/— 1,. .., 1, 0; in the
lower, (/— 1)^, . . ., /^. In the upper row for r = 2, insert 1 (the remainder

K2 = 2Q2-\-K2',
K3 = 2Qs+Ks',

K2'^^K,+4,

K3' = 7^2+8,

If r is even, set r — 1 = Bi

r = l

c = 5

s = 4

4
5

3

6

2

7

1
8

0
9

r = 2

c = 5

s = 2

3
3

1
4

r = 3

c =

s =

0
3

i2'»Assoc. fran?. avanc. sc, 9, 1880, 185-9.

i25Nyt Tidsskrift for Mat., Kjobenhavn, 15 A, 1904, 36-40.

i^^Math. Quest. Educ. Times, 69, 1898, 87-8; (2), 22, 1912, 38-9, 84-6.

i^'Japanese manuscript, first half eighteenth century, Abhandl. Geschichte Math. Wiss., 30,

1912, 236-7. isoNoya Acta Eruditorum, 1769, 107-128.

"iNouv. Mem. Ac. BerHn, ann6e 1771, 1773, 323.
"2Jour. Nat. Phil. Chem. Arts (ed., Nicholson), 1, 1809, 1-4.

372 History of the Theory of Numbers. [Chap, xiv

on dmding/^ by 2), 1+2, 1+2+2 under 1, 3, 5 of the first row for r = l; in
the lower row, insert 4 (the quotient), 4 — 1, 4 — 2. To factor/^ — c, locate
the column headed by the given c; thus, for c = 3, the factors are s = 6,
r = 1 and s = 3, r = 2. Since c = 2 occurs only in the first row, 9 — 2 is prime.

Joubin,^^^ J. P. Kulik,^^^ 0. V. Kielsen,i36 ^^d G. K. Winter^^e published
papers not accessible to the author.

E. Lucas gave methods of factoring and tests for primes (Ch. XVII).

D. Biddle^" wrote the proposed number N in the form S^-\-A, where
S- is the largest square < A^. Write three rows of numbers, the first begin-
ning with A, or A —S if A >S; the second beginning with S (or S+1) and
increasing by 1 ; the third beginning with S and decreasing by 1. Let A^,
B„, C„ be the nth elements in the respective rows. Then

except that, when i4„>C„, we subtract C„ from An as often (say k times)
as will leave a positive remainder, and then B„ = 5„_i + 1+A:. WTien we
reach a value of n for which i4„ = 0, we have N = BJJn- For example, if
iV = 589 = 24H 13, the rows are

13 14 17 1 9 0

24 25 26 28 29 31 (factors 31, 19).
24 23 22 21 20 19
It may prove best to start with 2N instead of with N.
O. Meissner^^^ reviewed many methods of factoring.
R. W. D. Christie^^^ gave an obscure method by use of "roots."
Christie"" noted that, if N = AB,
A = {4hN+d''-d)/i2b), B = (46Ar+dHd)/2, d=a-hc,

whence d'' = {B-h Ay.

D. Biddle"^ gave a method of finding the factors of N given those of
AT+l. SetL = iV-l. Try to choose i^ and M so that i(:iV/ = iV+ 1 and
so that 1 +Z is a factor of N. Since 2N={l-\-K) M-\-L — M,we will have
L-M=il+K)m, whence 2N={l+K){M+m). For iV=1829, A^+1
= 2-3-5-61. Take K = 30, M = 61. Then m = 57, M+w = 2-59, iV = 31-59.
He gave {ibid., p. 43) the theoretical test that N = S^+A is composite if
the sum of r terms of

is an integer for some value of r.

'»*Sur lea facteura num6riques, Havre, 1831.

>«Abh. K. Bohm. Gesell. Wiss., 1, 1841 (2, 1842-3, 47, graphical determination of primes).

"HDra et heel tals upplosning i factorer, Kjobenhavn, 1841.

"•Madras Jour. Lit. Sc, 1886-7, 13.

"'Mesa. Math., 28, 1898-9, 116-20; Math. Quest. Educat. Timea, 70, 1899, 100, 122; 75, 1901,

48; extension, (2), 29, 1916, 43-6.
"«Math. Naturw. Blatter, 3, 1906, 97, 117, 137.
"'Math. Quest. Educat. Times, (2), 12, 1907, 90-1, 107-8.
"o/bid., (2), 13, 1908, 42-3, 62-3.
"i/btd., (2), 14, 1908, 34. The process is well adapted to factoring 2P-1, (2), 23, 1913, 27-8.

I

Chap. XIV] METHODS OF FACTORING. 373

E. Lebon^^^" would first test AT for prime factors P just < VN. Let
Q be the quotient and R the remainder on dividing N by P. If Q and R
have a common factor, it divides N) if not, N is not divisible by any factor
of Q or of R.

D. Biddle^^^ considered N = S'^+A = {S+u){S-v), wrote w = iVi and
obtained hke equations in letters with subscripts unity. Then treat
UiVi = N2 similarly, etc.

A. Cunningham^^^ noted that the number of steps in Biddle's^^^ process
is approximately the value of A; in 2''' = N, and developed the process.

E. Lebon^^^ treated the decomposition of forms

a:"±a:^±a;T± . . .±1 (a>|8>7...)

of degrees ^ 9 into two such forms, using a table of those forms of degrees
^ 4 with all coefficients positive which are not factorable. The base most
used in the examples is x = 10. But bases 2 and 3 are considered.

E. Barbette^^^ quoted from his^^^ text the theorem that any integer N
can be expressed in each of the four forms

where ^j: = x{x-\-l)/2. The resulting new methods of factoring are now
simplified by use of triangular and quadratic residues. The first formula
implies N={x—y){x-\ry+\)/2. In his text, he considered the sum

iv=(2/+i)+(y+2)+ . ..+{x-\)+x=^,-^y

of consecutive integers. Treating four types of numbers N, he proved that
this equation has 1, 2 or more than 2 sets of integral solutions x, y, according
as iV is a power of 2, an odd prime, or a composite number not a power of 2.
He proved independently, but again by use of sums of consecutive integers,
that every composite number not a power of 2 can be given the form* N = u
(2y — w+l)/2, where u and v are integers and v^u'^S. Solving for u, and
setting x = 2v-\-l, we get 2u = x+(x'^ — 8Ny^^. Hence x'^—SN = y^ is solva-
ble in integers [evidently by a: = 2A'+l, y = 2N—l]. Finally, Nz=Ax is
equivalent to (2a;+l)^ = 8A^2;+l. For four types of numbers N, the solu-
tions of y^ = SNz-\-l are found and seen to involve at least two arbitrary
constants.

A. Aubry^^^ reviewed various methods of factoring.

"wil Pitagora, Palermo, 14, 1907-8, 96-7.

i«Math. Quest. Educat. Times, (2), 19, 1911, 99-100; 22, 1912, 38-9; Educat. Times, 63, 1910,
500; Math. Quest, and Solutions, 2, 1916, 36-42.

"»/6id., (2), 20, 1911, 59-64; Educat. Times, 64, 1911, 135.

i^BuU. soc. philomathique de Paris, (10), 2, 1910, 45-53; Sphinx-Oedipe, 1908-9, 81-3, 97-101

"^L'enseignement math., 13, 1911, 261-277.

"^Les sommes de p-i&mes puissances distinctes ^gales k une p-ieme puissance, Paris, 1910, 20-76.
*This follows from the former result N = {x —y)(x+y +1) /2 by setting x=v, y = v—u. To
give a direct proof, take u to be the least odd factor > 1 of the composite number N not
a power of 2; then q = N /u can be given the form y — (u— 1)/2 by choice of y. If t;<M,
then g<(«+l)/2<u, so that q has no odd factor and 2 = 2''. But N='2^U is of the
desired form if we take v^u/2'^N.
"'Sphinx-Oedipe, num^ro sp6c., June, 1911, 1-27. Errata and addenda, num6ro 3p6c., Jan.,
1912, 7-9, 14. L'enseignement math., 15, 1913, 202-231.

374 History of the Theory of Numbers. [Chap, xiv

S. Bisman^"** noted that N is composite if and only if there exist two
integers A, B such that A +2 B and A-\-2BN divide 2{N-1) and (A''-1)A,
respectively. But there is no convenient maximum for the smaller integer
B. To find the factor 641 of 2'^^ + l there are 16 cases.

A. G^rardin^^^ gave a report on methods of factoring.

J. A. Gmeiner,^^° to factor a, prime to 6, determined b and e so that
9a = 166+e, 0^€<16. Let cu^ be the largest square <6 and set b = oi^-\-p,
cr = p— CO. Hence 9a = 16(co — a:)(w+a;H-l)+r(a:), where

t(x) = 16(7+€+16x(x+1).

Since t{x)=t{x — 1)+S2x, we may rapidly tabulate the values of r(x) for
x = 0, 1, 2, . . . . If we reach the value zero, we have two factors of a. To
prove that a is a prime, we need extend the table until co+x + l is the
largest square <a. To modify the process, use 4a = 76 + €.

A. Reymond^^^ used the graphs of y = x/n (n = l, 2, 3, 5, . . .)> marking
on each the points with integral coordinates. He omitted y = x/4: since
its integral points are ony = x/2. Since 17 is not the abscissa of an integral
point on y = x/n for l<n< 17, 17 is a prime. [Mobius^^" of Ch. XIII.]

A. J. Kempner^^^ found, by use of a figure perspective to Reymond's^^^
how to test the primality of numbers by means of the straight edge.

D. Biddle and A. Cunningham^^^ factor a product A^ of two primes by
finding A^i<A^ and N2>N such that N2-N = N-Ni+2, while each of Ni
and A''2 is a product of two even factors, the two smaller factors differing
by 2 and the two larger factors differing by 2.

'"Mathesis, (4), 2, 1912, 58-60.
"'Assoc. fraiiQ. avanc. sc, 41, 1912, 54-7.
"oMonatshefte Math. Phys., 24, 1913, 3-26.
»"L'enseignement math., 18, 1916, 332-5.
'"Amer. Math. Monthly, 24, 1917, 317-321.
'"Math. Quest, and Solutions, 3, 1917, 21-23.

I

CHAPTER XV.

FERMAT NUMBERS F„ = 2'"+l.

Fermat^ expressed his belief that every F^ is a prime, but admitted
that he had no proof. Elsewhere^ he said that he regarded the theorem
as certain. Later^ he impHed that it may be proved by "descent." It
appears that Frenicle de Bessy confirmed this conjectured theorem of Fer-
mat's. On several occasions Fermat^ requested Frenicle to divulge his proof,
promising important applications. In the last letter cited, Fermat raised
the question if (2/0)^""+ 1 is always a prime except when divisible by an F„.

C. F. Gauss^ stated that Fermat affirmed (incorrectly) that the theorem
is true. The opposite view was expressed by P. Mansion^ and R. Baltzer.'^

F. M. Mersenne^ stated that every F^ is a prime. Chr. Goldbach^
called Euler's attention to Fermat's conjecture that F„ is always prime, and
remarked that no F^ has a factor < 100; no two F^ have a common factor.

L. Euler^o found that

^5 = 2^2+1 = 641-6700417.

Euler^^ proved that if a and h are relatively prime, every factor of
a^ +6^ is 2 or of the form 2"+^ A: + land noted that consequently any
factor of F5 has the form 64fc + l, k = 10 giving the factor 641.

Euler^^" and N. Beguelin^^ used the binary scale to find the factor
641 = 1+2^+2^ of F5.

C. F. Gauss^^ proved that a regular polygon of m sides can be constructed
by ruler and compasses if m is a product of a power of 2 and distinct odd
primes each of the form F„, and stated that the construction is impossible
if m is not such a product. This subject will be treated under Roots of Unity.

Sebastiano Canterzani^^ treated twenty cases, each with subdivisions
depending on the final digits of possible factors, to find the factor 641 of F^,

iQeuvres, 2, 1894, p. 206, letter to Frenicle, Aug. (?) 1640; 2, 1894, p. 309, letter to Pascal,
Aug. 29, 1654 (Fermat asked Pascal to undertake a proof of the proposition, Pascal,
III, 232; IV, 1819, 384); proposed to Brouncker and Wallis, June 1658, Oeuvres, 2,
p. 404 (French transl., 3, p. 316). Cf. C. Henry, BuU. Bibl. Storia So. Mat. e Fis., 12, 1879,
500-1, 716-7; on p. 717, 42 ... 1 should end with 7, ihid., 13, 1880, 470; A. Genocchi, Atti
Ac. Sc. Torino, 15, 1879-80, 803.

^Oeuvres, 1, 1891, p. 131 (French transl., 3, 1896, p. 120).

^Oeuvres, 2, 433-4, letter to Carcavi, Aug., 1659.

^Oeuvres, 2, 208, 212, letters from Fermat to Frenicle and Mersenne, Oct. 18 and Dec. 25, 1640.

^Disq. Arith., Art. 365. Cf. Werke, 2, 151, 159. Same view by Klugel, Math. Worterbuch,
2, 1805, 211; 3, 1808, 896.

«Nouv. Corresp. Math., 5, 1879, 88, 122.

'Jour, fur Math., 87, 1879, 172.

^Novarum Physico-Mathematicarum, Paris, 1647, 181.

^Corresp. Math. Phys. (ed., Fuss), I, 1843, p. 10, letter of Dec. 1729; p. 20, May 22, 1730; p. 32,
July 1730.

"Comm. Ac. Petrop., 6, ad annos 1732-3 (1739), 103-7; Comm. Arith. Coll., 1, p. 2.

"Novi Comm. Petrop., 1, 1747-8, p. 20 [9, 1762, p. 99); Comm. Arith. CoU., 1, p. 55 [p. 357].
""Opera postuma, I, 1862, 169-171 (about 1770).

"Nouv. Mem. Ac. Berlin, ann^e 1777, 1779, 239.

"Disq. Arith., 1801, Arts. 335-366; German transl. by Maser, 1889, pp. 397-448, 630-652.

"Mem. 1st. Naz. Italiano, Bologna, Mat., 2, II, 1810, 459-469.

375

376 History of the Theory of Numbers. [Chap, xv

and proved in the same lengthy dull manner that the quotient is a prime.
An anonymous writer^^ stated that

(1) 2+1, 2-+1, 2-'+l, 22''+!,...

are all primes and are the only primes 2*+l. See Malvy.'^

Joubin^^ suggested that these numbers (1) are possibly the ones really
meant by Fermat/ evidently without having consulted all of Fermat's
statements.

G. Eisenstein^' set the problem to prove that there is an infinitude of
primes F„.

E. Lucas^^ stated that one could test the primality of F^ in 30 hours by
means of the series 3, 17, 577, . . . , each term being one less than the double of
the square of the preceding. Then F„ is a prime if 2""^ is the rank of the first
term divisible by F„, composite if no term is di\'isible by F„. Finally, if a is
the rank of the first term divisible by F„, the prime divisors of F„ are of the
form 2''g + l, where A; = a+1 [not A: = 2°+^]. See Lucas."

T. Pepin^^ stated that the method of Lucas^^ is not decisive when F„
divides a term of rank a<2''~^; for, if it does, we can conclude only that the
prime di\'isors of F„ are of the form 2''"''^g'+l, so that we can not say whether
or not F„ is prime if a +2 ^2""^. We may answer the question unambigu-
ously by use of the new theorem: For n> 1, F„ is a prime if and only if it
divides

where k is any quadratic non-residue of Fn, as 5 or 10. To apply this test,
take the minimum residues modulo F„ of

2"-l

A/, i^ ) "^ ) • • • } '^ '

Proof was indicated by Lucas-^ of Ch. XVII, and by Morehead.^^
J. Pervouchine^° (or Pervusin) announced, November 1877, that

Fi2=0 (mod 114689 = 7-2^^+1).

E. Lucas^^ announced the same result two months later and proved that
every prime factor of F„ is = 1 (mod 2"'^^).

Lucas^^ employed the series 6, 34, 1154, . . . , each term of which is 2 less
than the square of the preceeding. Then F„ is a prime if the rank of the first
term divisible by F^ is between 2""^ and 2" — !, but composite if no term is
di\'isible by F„. Finally, if a is the rank of the first term divisible by F„

"Annales de Math. (ed. Gergonne), 19, 1828-9, 256.

"M^moire sur le3 facteurs numdriques, Havre, 1831, note at end.

»'Jour. fiir Math., 27, 1844, 87, Prob. 6.

"€omptes Rendus Paris, 85, 1877, 136-9.

'•Comptea Rendus, 85, 1877, 329-331. Reprinted, with Lucas" and Landry," Sphinx-Oedipe,

5, 1910, 33-42.
"Bull. Ac. St. Pdtersbourg, (3), 24, 1878, 559 (presented by V. Bouniakowsky). Melanges

math. ast. sc St. P^tersbourg, 5, 1874-81, 505.
"Atti R. Accad. Sc. Torino, 13, 1877-8, 271 (Jan. 27, 1878). Cf. Nouv. Corresp. Math., 4,

1878, 284; 5, 1879, 88. See Lucas" of Ch. XVIL
"Amer. Jour. Math., 1, 1878, 313.

Chap. XV] FerMAT NUMBERS F„=2^" + l. 377

and if a<2''~\ the prime divisors of F„ are of the form* 2*^+1, where
k = a-\-l [cf . Lucas^^]. He noted (p. 238) that a necessary condition that F^
be a prime is that the residue modulo F^ of the term of rank 2" — 1 in this
series is zero. He verified (p. 292) that F^ has the factor 641 and again
stated that 30 hours would suffice to test Fq.

F. Proth^^ stated that, if A; = 2", 2^+1 is a prime if and only if it divides
m = 3^ ~ + 1 . He^^ indicated a proof by use of the series of Lucas defined by
Uo = 0, Ui = l, . . . , w„ = 3if„_i + l and the facts that Up_i is divisible by
the prime p, while m=^U2^lu2^-^. Cf. Lucas. ^^

E. Gelin^^ asked if the numbers (1) are all primes. Catalan^^ noted
that the first four are.

E. Lucas^^ noted that Proth's^^ theorem is the case A; = 3 of Pepin's. ^^
Pervouchine" announced, February 1878, that 7^23 lias the prime factor

5.225+1 = 167772161.

W. Simerka^^ gave a simple verification of the last result and the fact
(Pervouchine^o) that 7-2'Hl divides F^^.

F. Landry, ^^ when of age 82 and after several months' labor, found that

7^6 = 274177-67280421310721,

the first factor being a prime. He and Le Lasseur and G^rardin^^" each
proved that the last factor is a prime (cf. Lucas^^).

K. Broda^" sought a prime factor p of a^^+1 by considering

n = (a^2-l)(a«Hl)(a'''+a^''+a2^«+a^''+l).

Multiply by i^ = (o^2_}_l)/p. Thusnw = (a^^°-l)/p. But a^^°^l (mod641).
Since each factor of n is prime to p, we take a = 2 and see that 2^^+ 1 is divis-
ible by 641.

E. Lucas^^ stated that he had verified that F^ is composite by his^^ test,
before Landry found the factors.

P. Seelhoff^^ gave the factor 5-2^^+1 of F^,^ and commented on Beguelin.^^

*Lucas wrote fc = 2"+^ in error, as noted by R. D. Carmichael on the proof-sheets of this
History.

23Comptes Rendus Paris, 87, 1878, 374.

«Nouv. Corresp. Math., 4, 1878, 210-1; 5, 1879, 31.

MUd., 4, 1878, 160.

^HUd., 5, 1879, 137.

"Bull. Ac. St. P6tersbourg, (3), 25, 1879, 63 (presented by V. Bouniakowsky) ; Melanges math,
astr. ac. St. P^tersbourg, 5, 1874-81, 519. Cf. Nouv. Corresp. Math., 4, 1878, 284-5; 5,
1879, 22.

28Casopi3, Prag, 8, 1879, 36, 187-8. F. J. Studnicka, iUd., 11, 1881, 137,

"Comptes Rendus Paris, 91, 1880, 138; Bull. Bibl. Storia Sc. Mat., 13, 1880, 470; Nouv. Cor-
resp. Math., 6, 1880, 417; Lea Mondes, (2), 52, 1880. Cf. Seelhoflf, Archiv Math. Phys.,
(2), 2, 1885, 329; Lucas, Amer. Jour. Math. 1, 1878, 292; R6cr6at. Math., 2, 1883,
235; I'intermddiaire des math., 16, 1909, 200.

»»Sphinx-Oedipe, 5, 1910, 37-42.

"Archiv Math. Phys., 68, 1882, 97.

"Recreations Math., 2, 1883, 233-5. Lucas,"* 354-5.

»2Zeitschr. Math. Phys., 31, 1886, 172-4, 380. For Ft, p. 329. French transl., Sphinx-Oedipe,
1912, 84-90.

378 History of the Theory of Numbers. [Chap, xv

J. Hermes^^ indicated a test for composite F„ by Fermat's theorem.

R. Lipschitz^ separated all integers into classes, the primes of one class
being Fermat numbers F„, and placed in a new light the question of the
infinitude of primes F„.

E. I.ucas^^ stated the result of Proth,-^ but with a misprint [Cipolla^^].
H. Scheffler^^ stated that Legendre believed that every F„ is a prime(!),

and obtained artificially the factor 641 of F5. He noted (p. 167) that

F„F„+, . . .F„_, = l+22"+22-2"+23-2''+ . . . +2^"-2".
He repeated (pp. 173-8) the test by Pepin/^ with k = 3, and (p. 178) expressed
his belief that the numbers (1) are all primes, but had no proof for Fie-

W. W. R. Ball" gave references and quoted known results.

T. M. Pervouchine^^ checked his verification that F12 and F23 are com-
posite by comparing the residues on di\'ision by 10^ — 2.

Mah'y^^ noted that the prime 2^+1 is not in the series (1).

F. Klein^° stated that F7 is composite.

A. Hurwitz"*^ gave a generalization of Proth's^^ theorem. Let F„(x)
denote an irreducible factor of degree 4>{n) of x" — 1. Then if there exists
an integer q such that Fp_i(g) is divisible by p, p is a prime. When
p = 2'-+l,Fp_i(x)^=x''"' + l.

J. Hadamard'*- gave a very simple proof of the second remark by Lucas. ^^

A. Cunningham^^ found that Fn has the factor 319489-974849.

A. E. \Yestern^ found that Fg has the factor 2^^-37 + 1, Fis the factor
2'°-13 + l, the quotient of Fn by the known factor 2^'*-74-l has the factors
2^^-397+1 and 2^^-7-139 + l. He verified the primality of the factor 2^^-3-f 1
of F38, found by J. Cullen and A. Cunningham. He and A. Cunningham
found that no more F„ have factors < 10^ and similar results.

m-2

M. Cipolla^^ noted that, if g is a prime >(9"^ -l)/2'"+^and m>\,
2'"g+ 1 is a prime if and only if it divides 3H 1 for k = ^•2'"+^ He^^ pointed
out the misprint in Lucas'^^ statement.

Nazarevsky^^ proved Proth's-^ result by using the fact that 3 is a primi-
tive root of a prime 2''+l.

"Archiv Math. Phys., (2), 4, 1886, 214-5, footnote.

"Jour, fur Math., 105, 1889, 152-6; 106, 1890, 27-29.

"Th^orie des nombres, 1891, preface, xii.

»«Beitrage zur Zahlentheorie, 1891, 147, 151-2, 155 (bottom), 168.

»^Math. Recreations and Problems, ed. 2, 1892, 26; ed. 4, 1905, 36-7; ed. 5, 1911, 39-40.

"Math. Papers Chicago Congress of 1893, I, 1896, 277.

"L'interm6diaire des math., 2, 1895, 41 (219).

"Vortrage iiber aiisgewahlte FragenderElementar Geometric, 1895, 13; French transl., 1896, 26;

English transl., "Famous Problems of Elementary Geometry," by Beman and Smith,

1897, 16.
"L'interm^diaire des math., 3, 1896, 214.
«/6u/., p. 114.
"Report British Assoc, 1899, 653-4. The misprint in the second factor has been corrected

to agree with the true " value 2".7.17 + 1.
^Cunningham and Western, Proc. Lond. Math. Soc, (2), 1, 1903, 175; Educ. Times, 1903, 270.
«Periodico di Mat., 18, 1903, 331.
"Also in Annali di Mat., (3), 9, 1904, 141.
*'L'interm6diaire des math., 11, 1904. 215.

Chap. XV] FeRMAT NUMBERS F„ = 2^" + l. 379

A. Cunningham^^" noted that 3, 5, 6, 7, 10, 12 are primitive roots and
13, 15, 18, 21, 30 are quadratic residues of every prime F„>5. He fac-
tored F4' + S+iFoFiF2Fz)\

Thorold Gosset^^ gave the two complex prime factors a± 6i of the known
real factors of composite F„, n = 5, 6, 9, 11, 12, 18, 23, 36, 38.

J. C. Morehead'*^ verified by use of the criterion of Pepin^^ with k = S
that 7^7 is composite, a result stated by Klein.^°

A. E. Western^" verified in the same way that Fy is composite. The
work was done independently and found to agree with Morehead's.

J. C. Morehead^^ found that Fy^ has the prime factor 2^^-5+1.

A. Cunningham^^ considered hyper-even numbers

Eo, „ = 2", E,,n = 2^0. n, . . . , E^+,, „ = 2^r, n.

For m odd, the residues modulo m of Er,o, -E'r, i,- • • have a non-recurrent
part and then a recurring cycle.

A. Cunningham^^ gave tables of residues of Ei^ „, E2, n, Er, 0, 3^" and 5^"
for the n's forming the first cycle for each prime modulus < 100 and for
certain larger primes. A hyper-exponential number is like a hyper-even
number, but with base q in place of 2. He discussed the quadratic, quartic
and octic residue character of a prime modulo F^, and of F„ modulo Fn+x-

Cunningham and H. J. WoodalP^ gave material on possible factors of F^.

A. Cunningham^^ noted that, for every F„>5, 2Fn = t^ — (Fn — 2)u^
algebraically, and expressed F5 and Fq in two ways in each of the forms
a^+6^ c^±2d2. He^*^ noted that Fn^+E^^ is the algebraic product of
n-\-2 factors, where ^n = 2^", and that M„ = (F„H^„^)/(F„-fE„) is divisible
by Mn-r- If n — m^2, F„i'^-\-FJ is composite.

A. Cunningham^^ has considered the period of l/N to base 2, where N
is a product FmFm-i . ■ -Fm-r of Fermat numbers.

J. C. Morehead and A. E. Western^^ verified by a very long computation
that Fg is composite. Use was made of the test by Pepin^^ with A; = 3, which
was proved to follow from the converse of Fermat's theorem.

P. Bachmann^^ proved the tests by Pepin^^ and Lucas. ^^

A. Cunningham*^^ noted that every Fn>5 can be represented by 4
quadratic forms of determinants =^Gn, =*=2(r„, where Gn = FoFi. . .Fn-i-

Bisman^'^^ (of Ch. XIV) separated 16 cases in finding the factor 641 of F^.

^^'^Math. Quest. Educ. Times, (2), 1, 1902, 108; 5, 1904, 71-2; 7, 1905, 72.

"Mess. Math., 34, 1905, 153-4. "BuU. Amer. Math. Soc, 11, 1905, 543.

"Proc. Lond. Math. Soc, (2), 3, 1905, xxi.

"Bull. Amer. Math. Soc, 12, 1906, 449; Annals of Math., (2), 10, 1908-9, 99. French transl. in

Sphinx-Oedipe, Nancy, 1911, 49. ^^Report British Assoc. Adv. Sc, 1906, 485-6.

"Proc London Math. Soc, (2), 5, 1907, 237-274.
"Messenger of Math., 37, 1907-8, 65-83.
55Math. Quest. Educat. Times, (2), 12, 1907, 21-22, 28-31.
^HhU., (2), 14, 1908, 28; (2), 8, 1905, 35-6.
"Math. Gazette, 4, 1908, 263.

"Bull. Amer. Math. Soc, 16, 1909, 1-6. French transl., Sphinx-Oedipe, 1911, 50-55.
"Niedere Zahlentheorie, II, 1910, 93-95.
'"Math. Quest. Educat. Times, (2), 20, 1911, 75, 97-98.

380 History of the Theory of Numbers. [Chap, xv

A. G^rardin" noted that F„ = (240j+97)(240!/+161) for all the F„
fully factored to date, and specified x and y more exactly in special cases.

C. Henrv'^'- gave references and quoted known results.

R. D. CannichaeP' gave a test for the primality of F„ equivalent to
Pepin's^^ and a further generalization (p. 65) in the direction of Hurwitz's."

R. C. Archibald" cited many of the papers hsted above and collected in a
table the known factors of F„ with the exception of that given by Morehead."

For a remark on F„, see Cunningham^°^ of Ch. VII.

"Sphinx-Oedipe, 7, 1912, 13.
•HDeuvres de Fermat, 4, 1912, 202-4.
"Annals of Math., (2), 15, 1913-4, 67.
•'Amer. Math. Monthly, 21. 1914. 247-251.

CHAPTER XVI.

FACTORS OF a^^b\

Fermat^ stated that (2''+l)/3 has no factors other than 2kp+l if p is
an odd prime.

L. Euler^ noted that o*+46* has the factors a^=i=2ah+2b^.

Euler^ discussed the numbers a for which a^ + 1 is divisible by a prime
4n+l=r^+s^. Let p/q be the convergent preceding r/s in the continued
fraction for r/s ; then ps — qr==^l. Thus every a is of the form (4n + 1 ) m ±
k, where k = pr+qs.

Euler^ gave the 161 integers a< 1500 for which a^ + 1 is a prime, and the
cases a = 1, 2, 4, 6, 16, 20, 24, 34 for which a*+l is a prime.

Euler^ proved that, if m is a prime and a, b are relatively prime, a factor
of a"* — 6"", not a divisor of a — 6, is of the form kn-\-l. If p = A;n + 1 is a prime
and a =p=^ pa, then a*' — 1 is divisible by p. If of" — bg"" is divisible by a prime
p = 'mn-{-l, while/ and g are not both divisible by p, then a"" — 6"" is divisible
by p ; the converse is true if m and n are relatively prime.

Euler^ proved the related theorems: For q an odd prime, any prime
divisor of a^—1, not a divisor of a — 1, is of the form 2nq-\-l. If a"" — 1 is
divisible by the prime p = m7i+l, we can find integers x, y not divisible by
p such that A = ax'*— ?/" is divisible by p (since the quotient of a'"^""'— 2/"*"
by A is not divisible by p\i x,y are suitably chosen) .

Euler^ treated the problem to find all integers a for which a^ + 1 is divisible
by a given prime 4n + 1 = p^ + ?^- If a^ + b^ is divisible by p'^-\-(f', there exist
integers r, s such that a = pr+g's, 6 = ps—gr. We wish 6= =±=1. Hence we
take the convergent r/s preceding p/q in the continued fraction for p/q.
Thus ps — qr=^\, and our answer is a= ± {pr-\-qs). He listed all primes
P = 4n+1<2000 expressed as p^+g^, and listed all the a's for which a^ + 1
is divisible by P. The table may be used to find all the divisors < a of a
given number a^+1. He gave his^ table and tabulated the values a< 1500
for which {a'^-\-l)/k is a prime, for k=2, 5, 10. He tabulated all the
divisors of a^+1 for a^ 1500.

N. Beguelin^ stated that 2''+l has a trinary divisor 1+2^+2' only when
n=10, 24, 32, although his examples (p. 249) contradict this statement.

Euler^ gave a factor of 2"=^ 1 for various composite n's.

iQeuvres, 2, 205, letter to Frenicle, Aug. (?), 1640. Bull. Bibl. St. Sc. Mat. e Fis., 12, 1879, 716.

''Corresp. Math. Phys. (ed., Fuss), I, 1843, p. 145; letter to Goldbach, 1742.

^lUd., 242-3; letter to Goldbach, July 9, 1743.

mid., 588-9, Oct. 28, 1752. Published, Euler.^

^Novi Comm. Petrop., 1, 1747-8, 20; Coram. Arith. Coll., 1, 57-61, and posthumous paper,

ibid., 2, 530-5; Opera postuma, I, 1862, 33-35. Cf. Euleri^z of Ch. VII and the topic

Quadratic Residues in Vol. III.
«Novi Comm. Petrop., 7, 1758-9 (1755), 49; Comm. Arith., 1, 269.
^Novi Comm. Petrop., 9, 1762-3, 99; Comm. Arith., 1, 358-369. French transl., Sphinx-

Oedipe, 8, 1913, 1-12, 21-26, 64.
»M6m. Ac. Berlin, annee 1777, 1779, 255. Cf. Ch. XV and Henry.i^
'Posthumous paper, Comm. Arith., 2, 551; Opera postuma, I, 1862, 51.

381

382 History of the Theory of Numbers. [Chap, xvi

Euler^" discussed the divisors of numbers of the iorm.fa^+gb'^.

Anton FelkeP" gave a table, incomplete as to a few entries, of the factors
ofa"-l,n = l,..., ll;a = 2,3,..., 12.

A. M. Legendre^^ proved that every prime divisor of a"+l is either of the
form 2nx-{-l or divides a"H-l where co is the quotient of n by an odd factor;
every prime divisor of a" — ! is either of the form nx-\-l or divides a'^ — l
where co is a factor of n. For n odd, the divisors must occur in 0(0"=^ 1)
= ?/'-± a and are thus further limited by his tables III-XI of the linear forms
of the divisors of <"±au".

C. F. Gauss^^ obtained by use of the quadratic reciprocity law the linear
forms of the divisors of x"— A.

Gauss^'^ gave a table of 2452 numbers of the forms a^+1, a^+4, . . .,
a^+81 and their odd prime factors p, for certain a's for which the p's are
all <200.

Sophie Germain^^ noted that p'*+4g* has the factors p^=^2pq+2^
[Euler^]. Taking p = l, q = 2\ we see that 2^'"''^+l has the two factors
22.+i±2'+i + l.

F. Minding^^ gave a detailed discussion of the linear forms of the divisors
of x^ — c, using the reciprocity law for the case of primes. He reproduced
(pp. 188-190) the discussion by Legendre.^^

P. L. Tchebychef^® noted that, if p is an odd prime, every odd prime
factor of a''— 1 is either of the form 2pz-\-l or is a factor of a — 1, and more-
over is a divisor of x^ — ay'^. Hence, for a = 2, it is of the form 2^2+1 and
also of one of the forms 8w=tl. Every odd prime factor of a^^+^ + l is
either of the form 2(2n+ 1)2+1 or a divisor of a+1 [cf. Legendre"].

V. A. Lebesgue^^ noted that the discussion of the linear forms of the
divisors of z^—D, where D is composite, is simplified by use of Jacobi's
generalization (a/b) of Legendre's symbol.

C. G. Reuschle^' denoted (x"''-l)/(x''-l) by FM. Set a = ah+bi,
6 = 0161+62, 61 = 0262+63,. ... If a, 6 are relatively prime,

(T^ ^r)C n = '^'^""nia(6-l-A)l+a;^ sVxjai(6i-l-A)|

{X —i){X —L) A=0 A=0

+ ... +a:^+^.+ - ■ -+^-2 Vx^'"-'n„_i {a._i(6„_i -1-A)} +x^+- • ■+^n-i.

9^'Opera postuma, I, 1862, 161-7 (about 1773).

loAbhandl. d. Bohmischen Gesell. Wiss., Prag, 1, 1785, 165-170.

'•Th6orie des nombres, 1798, pp. 207-213, 313-5; ed. 2, 1808, pp. 191-7, 286-8. German

transl. by Mascr, p. 222.
"Disq. Arith., 1801, Arts. 147-150.
"Werke, 2, 1863, 477-495. Schering, pp. 499-502, described the table and its formation by

the compo.sition of binary forms, e. g., (a^' + l) { (a4-l)^4-l} = {a(o + l)+l}* + l.
"Manuscript 9118 fonds frangais Bibl. Nat. Paris, p. 84. Cf. C. Henry, Assoc, frang. avanc.

sc, 1880, 205; Oeuvres de Fermat, 4, 1912, 208.
"Anfangsgrunde dor Hoheren Arith., 1832, 59-70.
"Theorie der Congrucnzen, in Russian, 1849; in German, 1889; §49.
"Jour, de Math., 15, 1850, 222-7.
"Math. Abhandlung, Stuttgart, 1853, II, pp. 6-13.

Chap. XVI] FACTORS OF a" ±6". 383

Reuschle's^^ table A gives many factors of a^=tl, a*±l, a^±l, a^^ — 1
for a^lOO, and of a"-l for n^42, a = 2, 3, 5, 6, 7, 10.

Lebesgue^^" proved that x*^^+ . . .-\-x-\-l has no prime divisor other
than the prime p and numbers of the form kp + 1.

Jean Plana^^ gave S^^ + l =4-6091g, S^^-l=2-59r, and stated that q
is a prime and that r has no factor < 52259. But Lucas^^ noted that

q = 523-5385997, r = 28537-20381027.

E. Kummer^^ proved that there is no prime factor, other than t and
numbers 2m^±l, of the cyclotomic function

obtained from (a' — l)/(a — 1) by settinga+a~^ = a:;, t being a prime 2e + l.

E. Catalan^^ stated that, if n = a=Fl is odd, a"=Fl is divisible by n^, but
not by nK Proof by Soons, Mathesis, (3), 2, 1902, 109.

H. LeLasseur and A. Aurifeuille^^ noted that 2^"'''^ + l has the factors
22n+i± 2^^+1 + 1 [cf. Euler,2 S. Germain^^].

E. Lucas^^ proved that (2^°+l)/(2^+l) is a prime and gave the factors of
30^^±1, 2*^ + 1.

Theorems by Lucas on the factors of a" ±6**, given in various papers in
1876-8, are cited in Ch. XVII.

Lucas^^ factored (2m)"'=tl for m = 7, 10, 11, 12, 14, 15, and corrected
Plana.20

Lucas^^ gave tables due to LeLasseur and Aurifeuille of functions

5!il! („odd), ^^,

x^y x^-i-y^

expressed in the form V^^pxyZ^, which is factorable if xy = ptP. Factors
of x^°-\-y^^ are given for various x's, y's. He gave LeLasseur's table of the
proper divisors of 2" — 1 for all odd values of n<100 except n = 61, 67,
71, 77, 79, 83, 85, 89, 93, 97; the proper divisors of 2"+l for n odd and <71
(except n = 61, 67) and for n = 73, 75, 81, 83, 99, 135; the proper divisors
of 22^1 for 2A;^74 (except 64, 68) and for 2k = 7S, 82, 84, 86, 90, 94, 102,
126, etc. Lucas proved (pp. 790-4) that the proper divisors of 2^"+l are of
the form 16ng + l, those of (j2a6n_|_^2a67i ^^.^ q£ ^^^q form Sahnq-j-l; for n odd,
those of a"^"+6"^'^ are of the form 4a6ng + l if a6 = 4/i + l, those of a"''" -6"'''*
are of the form 4a6ng + l if a6 = 4/i+3.

I'Math. Abhandlung . . .Tabellen, Stuttgart, 1856. Full title in Ch. I.

"aComptes Rendus Paris, 51, 1860, 11.

20Mem. Accad. Sc. Torino, (2), 20, 1863, 139-141.

"Cf. Bachmann, Kreistheilung, Leipzig, 1872.

22Revue de I'lnstruct. publique en Belgique, 17, 1870, 137; Melanges Math., ed. 1, p. 40.

23Atti R. Ac. Sc. Torino, 8, 1871; 13, 1877-8, 279. Nouv. Corresp. Math., 4, 1878, 86, 98.

Cf. Lucas,25 p. 238; Lucas,^^ 784.
2^Nouv. Ann. Math., (2), 14, 1875, 523-5.
25Amer. Jour. Math., 1, 1878, 293.
26Bull. Bibl. Storia Sc. Mat. e Fis., 11, 1878, 783-798.

384 History of the Theory of Numbers. [Chap. XVI

Lucas" gave the factors of 2'"+! for w =4n^60 and for 72, 84; also for
rM=4n+2^102 and for 110, 114, 126, 130, 138, 150, 210.

E.Catalan=« noted that x^+2{q-r)x^-^q~ for x^ ^ (2r)2*+i has the rational
factors (2r)^*'*"^ =*= (2r)*"'"^ +5. The case r = q = \ gives LeLasseur's^^ formula.
Again, 3'*+' + l has the factors ^^'^' + \, 32'^+^±3*+^ + l.

S. R^alis-^'' deduced LeLasseur's'-^ formula and 24"+22"+l=n(22''±
2"+l).

J. J. Sylvester'^^ considered the cyclotomic function ypt{x) obtained by
setting a + a"' =x in the quotient by a*""^ of

(a'-l)n(a'^''''''-l)
(1) ^.(a)=^" n(a'^'-l). (^ = P^'- • P"'"^'

where Pi,- ■ ■, Pn are distinct primes. He stated that every di\'isor of i/'t(x)
is of the form kt^ 1, with the exception that, if t = p\p=^l)/m, p is a divisor
(but not p^). Conversely, every product of powers of primes of the form
kt^l is a divisor of i/',(x). Proofs were given by T. Pepin, ibid., 526; E.
Lucas, p. 855; Dedekind, p. 1205 (by use of ideals). Lucas added that
p = 2^''+3 — 1 and p = 2^^''"''^ — 1 are primes if and only if they divide </'p+i(x)
for x = \/^ and x = 3\/^, respectively.

A. Lefebure^° determined poljTiomipls having no prime factor other than
those of the form HT+1, where H is given. First, let T = n\ where n is a
prime. For A, B relatively prime integers,

/ln_ Dn

has, besides n, no prime factor except those of the form Hn*+1, when A
and B are exact n'~Hh powers of integers. Second, let T = n'm^, where n, m
are distinct primes. The integral quotient of F^iu'", v'") by F„(w, t') has only
prime factors of the form Hn^m^ + l if u, v are powers of relatively prime
integers with the exponent w''~^n'~^ Similarly, if T is a product of powers
of several primes.

Lef^bure^^ discussed the decomposition into primes of U^ — V^, where
U, V are powers whose exponents involve factors of R.

E. Lucas^- stated that if n and 2/1 + 1 are primes, then 2n + l is a factor
of 2** — 1 or 2"+l according as n=3 or n=l (mod 4). If n and 4n + l are
primes, 4n + l is a factor of 2^''+l. If n and Sn + l =.4^ + 165^ are primes,
then 8n + l is a factor of 22" + 1 if B is odd, of 2-"± 1 if 5 is even. Also ten
theorems stating when Qn + l=U.^+SM^, 12n + l=L^-\-12M^ or 24n + l
= L'^-\-4SM^ are prime factors of 2'"'±1 for certain k's.

*'Sur la s^rie r^currente de Fermat, Rome, 1879, 9-10. Report by Cunningham.*'

"Aesoc. fran^. avanc. sc, 9, 1880, 228.

»»^Nouv. Ann. Math., (2), 18, 1879, 500-9.

"Comptes Rendus Paris, 90, 1880, 287, 345; Coll. Math. Papers, 3, 428. Incomplete in Math.

Quest. Educ. Times, 40, 1884, 21.
"Ann. 8C. 6cole norm, sup., (3), 1, 1884, 389-404; Comptea Rendus Paris, 98, 1884, 293, 413,

567, 613.
".\nn. BC. 6cole norm, sup., (3), 2, 1885, 113.
"Assoc, franc, avanc. sc, 15, 1886, II, 101-2.

Chap. XVI] FACTORS OF a" ±6". 385

A. S. Bang^^ discussed F<(a) defined by (1). If p is a prime, F^i^{a) has
only prime factors ap*+l if c? = a^ ~ —1 is prime to p, but has the factor p
(and not p^) if d is divisible by p.

Bang^^ proved that, if a>l, t>2, Ft{a) has a prime factor a^+1 except
forF6(2).

L. Gianni^^ noted that if p is an odd prime dividing a — 1 and p" divides
aF — \, then p""^ divides a — 1.

L. Kronecker^^ noted that, if F^iz) is the function whose roots are the
<^(n) primitive nth roots of unity,

{x-yY^-^F^{^^=GAx,y')

is an integral function involving only even powers of y. He investigated the
prime factors q of Gn{x, s) for s given. If q is prime to n and s, then q is
congruent modulo n to Jacobi's symbol {s/q). The same result was stated
by Bauer.^^

J. J. Sylvester^^ called ^"" — 1 the mth Fermatian function of 6.

Sylvester^^ stated that, for 6 an integer 9^1 or —1,

ft =?JZi

contains at least as many distinct prime divisors as m contains divisors > 1 ,
except when 0= — 2, m even, and ^ = 2, m a multiple of 6, in which two cases
the number of prime divisors may be one less than in the general case.

Sylvester^" called the above 6^ a reduced Fermatian of injdex m. lim = np",
n not divisible by the odd prime p, 6^ is divisible by p", but not by p"'^^, if
0 — 1 is divisible by p. If m is odd and ^ — 1 is divisible by each prime factor
of m, then dm is divisible by m and the quotient is prime to m.

Sylvester^^" stated that if P=l+p+ . . .+p''~^ is divisible by q, and
p, r are primes, either r divides q — 1 or r=q divides p — l. li P=q^ and
p, r, j are primes, j is a divisor of q—r. R. W. Genese easily proved the
first statement and W. S. Foster the second.

T. Pepin^^ factored various a" — 1, including a = 79, 67, 43, n = 5; a = 7,
n = ll', a = S, 71 = 23; a = 5 or 7, w = 13 (certain ones not in the tables by
Bickmore^^) .

H. Scheffler*^ discussed the factorization of 2'"+! by writing possible
factors to the base 2, as had Beguelin.^ He noted (p. 151) that, if m = 2"~\
1^2(2-+!'" = (i+2")2{i_2m+(2m-l)2"-(2m-2)22"

I o o(2m— 2)n_|_o(2m— l)n)

His formula (top p. 156), in which 2^*"^ is a misprint for 2^''"^ is equivalent
to that of LeLasseur.^^

"Tidsskrift for Mat., (5), 4, 1886, 70-80. ^*Ibid., 130-137. sspgriodico di Mat., 2, 1887, 114.

36Berlin Berichte, 1888, 417; Werke, 3, I, 281-292. "jour, fiir Math., 131, 1906, 265-7.

"Nature, 37, 1888, 152. ^Ubid., p. 418; CoU. Papers, 4, 1912, 628.

"Comptes Rendus Paris, 106, 1888, 446; CoU. Papers, 4, 607.

"«Math. Quest. Educ. Times, 49, 1888, 54, 69.

«Atti Accad. Pont. Nuovi Lincei, 49, 1890, 163. Cf. Escott, Messenger Math., 33, 1903-4, 49.

«Beitrage zur Zahlentheorie, 1891, 147-178.

386 History of the Theory of Numbers. [Chap, xvi

E. Lucas*^ gave algebraic factors of

K. Zsigmondy^ proved the existence of a prime dividing a'^ — h'^, but no
similar binomial with a lower exponent, exceptions apart (cf . Bang,^^- ^
Birkhoff^-).

J. W. L. Glaisher*^ gave the prime factors of p^ — ( — l)^?-^)/^ ^^^ ^^^^i

prime p<100.

T. Pepin^^ proved that (31'-l)/30, (83'-l)/82, (2*^ + l)/(3-83) are
primes.

A. A. Markoff'^^ investigated the greatest prime factor of n^+1.

W. P. Workman^^ noted the factors of 3^*+Hl [due to Catalan^^]
and 2^"* + l, and stated that Lucas^^ (p. 326) gave erroneous factors of 2'^^+l.

C. E. Bickmore*^ gave factors of a"-l for n^50, a = 2, 3, 5, 6, 7, 10,
11, 12.

Several^^" proved that n" — 1 is divisible by 4n+l if 47i+l is prime.

A. Cunningham^° gave 43 primes exceeding 9 milUon which are factors _
of (x5±l)/(x±l), and factors of 3'°+l, 3''-l, S^^+l, S'^^'+l, 5'^-l, ]
5^Hl, 5^'-l, S^^+l, 53^-1.

A. Cunningham^^ considered at length the factorization of Aurifeuillians,
i. e., the algebraically irreducible factors of

n+l

{n,7?Y^+ {2n^fT, (nix2)«+ ( - \)~{n^'\?r {n,n^ = n),

where n^ and x are relatively prime to ^2 and ?/, while n has no square factor,
and is odd in the second case. Aurifeuille had found them to be expressible
algebraically in the form P^ — Q'^. There are given factors of 2"+! for
n even and ^102, and for n = 110, 114, 126, 130, 138, 150, 210.

A. Cunningham^^ factored numbers a"=*= 1 by use of tables, complete to
p = 101, giving the lengths I of the periods of primes p and their powers
< 10000 to various bases q, so that q^= 1 (mod p or p^).

A. Cunningham and H. J. WoodalP^ gave factors of A^ = 2''10"±l for
x^30, a^ 10, and for further sets; also, for each prime p^3001, the least
a and the least corresponding x for which p is a divisor of N. Bickmore
(p. 95) gave the linear and quadratic forms of factors of A^.

T. Pepin^ factored a^-1 for a = 37, 41, 79; also^^ 151^-1.

"Th^orie des nombres, 1891, 132, exs. 2-4.

"Monatshefte Math. Phys., 3, 1892, 283. Details in Ch. VII, Zsigmondy."

«Quar. Jour. Math., 26, 1893, 47.

*«Memorie Accad. Pont. Nuovi Lincei, 9, I, 1893, 47-76.

♦^Comptea Rendus Paris, 120, 1895, 1032. "Messenger Math., 24, 1895, 67.

"/6id., 25, 1896, 1-44; 26, 1897, 1-38; French transl., Sphinx-Oedipe, 7, 1912, 129-44, 155-9.

"^Math. Quest. Educ. Times, 65, 1896, 78; (2), 8, 1905, 97.

»»Proc. London Math. Soc., 28, 1897, 377, 379. "/bid., 29, 1898, 381-438.

"Messenger Math., 29, 1899-1900, 145-179. The line of iV' = 532(p. 17) is incorrect.

"Math. Quest. Educat. Times, 73, 1900, 83-94. [Some errors.]

"Mem. Pont. Ac. Nuovi Lincei, 17, 1900, 321-344; errata, 18, 1901. Cf. Sphinx-Oedipe, 5,

1910, num6ro special, 1-9. Cf. Jahrbuch Fortschritte Math., on a = 37.
*»Atti Accad. Pont. Nuovi Lincei, 44, 1900-1, 89.

Chap. XVI] FACTORS OF a" =±=5". 387

A. Cunningham^^ factored 5'* — ! for n = 75, 105.

L. Kronecker^^" proved that every divisor, prime to <, of (1) is = 1 (mod t).
H. S. Vandiver^®'' noted that the proof applies to the homogeneous form
Ft{a, b) of (1) if a, b are relatively prime.

D. Biddle^^ gave a defective proof that 3-2^^+1 is a prime.

The Math. Quest. Educational Times contains the factorizations of:

Vol. 66 (1897), p. 97, 2i55_i factor 3P. Vol. 68 (1898), p. 27, p. 112, 272o_i.
p. 114, 1012+4.

Vol. 69 (1898), p. 61, 3824+1; p. 73, x^-1, x = 500, 2000; p. 117, x'+y^; p. 118,
10^^+33, 33.IOI8+I.

Vol. 70 (1899), p. 32, p. 69, 242i''+l; p. 47, 3201^-1; p. 64, 2^2+1, 8i*+l,
20018+1; p. 72, 2014-1; p. 107, 9721^+1. Vol. 71 (1899), p. 63, x^^+^-l;p. 72,
x'-\-y\

Vol. 72 (1900), p. 61, (Sny^-l factor 24n+l if prime; p. 86, 72210+1; p. 117,
144010+1.

Vol. 73 (1900), p. 51, 3520+I; p. 96, 711-I; p. 104, p. 114, x'-\-y*.

Vol. 74 (1901), p. 27, a prime 2iq+l divides g^-1 if k = 2^-^; p. 86, rcio-5y.

Vol. 75 (1901), p. 37, 3^+y'; p. 90, 1792^+1; p. Ill, 7^5+1. [Educ. Times,
(2), 54, 1901, 223, 260].

Ser. 2, Vol. 1 (1902), p. 46, 10082«+1; p. 84, x'-\-fxy^. Vol. 2 (1902), p. 33, p.
53, iV4+l; p. 118, IP^+l.

Vol. 3 (1903), p. 49, a'+b* (cf. 74, 1901, 44); p. 114, a«+l, a = 60000.

Vol. 6 (1904), p. 62. 9618+1.

Vol. 7 (1905), p. 62, 20813-1; pp. 106-7, 2126+I.

Vol. 8 (1905), p. 50, 9618+1; p. 64, 212^+1.

Vol. 10 (1906), p. 36, 5418+I, 6^4+1.

Vol. 12 (1907), p. 54, 6*2+1, 24^0+1.

Vol. 13 (1908), p. 63, 106-7, S'*-\-2'\

Vol. 14 (1908), p. 17, 15018+1; p. 71, sextics; p. 96, 7^5+1.

Vol. 15 (1909), p. 57, S''-\-2'*; p. 33, 3111+I, 12*5+1; p. 103, 282i+l, 44ii+l,
630+1.

Vol. 16 (1909), p. 21, 1924+1.

Vol. 18 (1910), pp. 53-5, 102-3, x^-\-^y'; pp. 69-71, a:«+27?/«; p. 93, y^^-l.

Vol. 19 (1911), p. 103, c(^-\-y' = z^-\-w\ Vol. 23 (1913), p. 92, (x'^-Nx-^NY
-{-Nix^-Ny.

Vol. 24 (1913), pp. 61-2, x'^^^y^ y = 5, 7, 11, 13; pp. 71-2, a;i2+2«, x'^-\-S\
x3''+3i5.

Vol. 26 (1914), p. 23, x^^-{-l for fc = 6n+35^3^ p. 39, a;i2+6«; p. 42, xl0-5^
^14+7^ a:22+llii, a;26-13i3. Vol. 27 (1915), pp. 65-6, 451^-1, 20''-l, fc^o+l for A;
= 6, 8, 10; p. 83, x4+4y4 (when four factors). Vol. 28 (1915), p. 72, 503o+l. Vol.
29(1916), p. 95, 9618+1.

New series, vol. 1 (1916), p. 86, rc2o+10i<', x28+14i4; pp. 94-5, x^'^-5^^, x^'^+WK

Vol. 2 (1916), p. 19, ajso-sis.

Vol. 3 (1917), p. 16, x''-y''; p. 52, xH-l.

E. B. Escott^^ gave many cases when 1+x^ is a product of two powers
of primes or the double of such a product.

«Proc. London Math. Soc, 34, 1901, 49.

^^''Vorlesungeu iiber Zahlentheorie, 1, 1901, 440-1.

s6*Amer. Math. Monthly, 10, 1903, 171.

"Messenger Math., 31, 1901-2, 116 (error); 33, 1903-4, 126.

"L'mterm^diaire des math., 7, 1900, 170.

388 History of the Theory of Numbers. [Chap, xvi

P. F. Teilhet*^ gave formulas factoring cases of l+ar^, as

(6H6+l)Hl = [(6+l)2-hl](6Hl),

4(c+ir+l =[(c+2)H(c+l)^[(c+l)Hca
the last being (10, 1903, 170) a case of the known formula for the product
of two sums of two squares (cf. 11, 1904, 50).

Escott^° repeated Euler's^ remarks on the integers x for which \-\-:i^
is di\'isible by a given prime. He and Teilhet (11, 1904, 10, 203) noted
that any common di\'isor of h and a±l di\'ides (a''='=l)/(a=fcl).

G. Wertheim" collected the theorems on the divisors of a"'=«=l.

G. D. Birkhoff and H. S. Vandiver^- employed relatively prime integers
a, 6 (a>6) and defined a primitive divisor of F„ = a" — 6" to be one relatively
prime to V^, for all di\'isors m of n. They proved that, if n?^2, F„ has a
primitive divisor 7^ 1 except f orn = 6, a = 2, 6 = 1.

L. E. Dickson^^'' noted that {p^ — l){p^ — l) has no factor=l (mod p^)
if p is prime.

A. Cunningham^^ gave high primes ?/" + l, (t/^+1)/2, ?/^4-y+l.

H. J. Woodall^ gave factors of ?/" + l.

J. W. L. Glaisher^^ factored 2^''=t2^+l for r^ll, in connection with
the question of the similarity of the nth pedal triangle to a given triangle.

L. E. Dickson^^ gave a new derivation of (1), found when F,(a) is divisible
by pi or pi^, where pi is a prime factor of t, and proved that, if a is an integer
>1, F,(a) has a prime factor not di\'iding 0*^ — 1 (m<t) except in the cases
f = 2, a = 2* — 1, and t = Q, a = 2; whence a' — 1 has a prime factor not dividing
a"*—l{m<t) except in those cases [cf. Birkhoff,^- CarmichaeP].

Dickson®^ applied the last theorem to the theory of finite algebras and
gave material on the factors of p" — 1.

A. Cunningham^^ treated at length the factorization of i/"+l for 71 = 2,
4, 8, 16, and (?/^''+l)/(2/"+l) for n = 1, 2, 4, 8, by means of extensive tables
of solutions of the corresponding congruences modulo p. He discussed also
x^+y", n = 4, 6, 8, 12.

Cunningham^^'' factored \{x^ — i^)/{x — y)-\-iJL{x^+y^)/{x'^+y'^) by ex-
pressing the fractions in the form P^ — kxyQ"^, k= o, 6.

"L'intermediaire des math., 9, 1902, 31&-8.

^oibid., 12, 1905, 38; cf. 11, 1904, 195-6.

"Anfangsgriinde der Zahlenlehre, 1902, 297-303, 314.

"Annals of Math., 5, 1903-4, 173. Cf. Zsigmondy," Dickson."

•«»Amer. Math. Monthly, 11, 1904, 197, 238; 15, 1908, 90-1.

•»Quar. Jour. Math., 35, 1904, 10-21.

•*Ibid., p. 95.

**Ibid., 36, 1905, 156.

"Amer. Math. Monthly, 12, 1905, 86-89.

•'Gottingen Nachrichten, 1905, 17-23.

"Messenger Math., 35, 1905-6, 16&-185; 36, 1907, 145-174; 38, 1908-9, 81-104, 145-175;

39, 1909, 33-63, 97-128; 40, 1910-11, 1-36. Educat. Times, 60, 1907, 544; Math. Quest.

Educat. Times, (2), 13, 1908, 95-98; (2), 14, 1908, 37-8, 52-3, 73^; (2), 15, 1909, 33-4,

103-4; (2), 17, 1910, 88, 99. Proc. London Math. Soc, 27, 1896, 98-111; (2), 9, 1910,

1-14.
•»<»Math. Quest. Educ. Times, 10, 1906, 58-9.

I

Chap. XVI] FACTORS OF a**=*=6''. 389

L. E. Dickson and E. B. Escott^^ discussed the divisibility of p^^* — 1
by d(p"^'^ — 1), where d is a divisor of n, and d of d.

R. D. CarmichaeF° proved that if P^^—R^" is divisible by 8a and we
set Q = {P''—R'')/{a{P — R) } , then Q/8 is an integer if and only if a is divisible
by the least integer e for which P^ — R^ is divisible by each prime factor of
a not dividing P — R, and 5 is a divisor of Q. Proof for the case R = l had
been given by E. B. Escott'^^

A. Cunningham^^ tabulated the factors of y^^^^l for ?/ = 2, 3, 5, 7, 12.

K. J. Sanjana'^^ considered the factors of

Sanjana'^^" applied his method to prove the statement of M. Kannan that
20^5-1= 11. 19-31-61-251421-3001-261451-64008001-3994611390415801

•4199436993616201.

L. E. Dickson''^ factored w"— 1 for various values of n.

R. D. CarmichaeF^ employed the methods of Dickson^ ^ to obtain general-
izations. Let Q„(a, /3) be the homogeneous form of Fn{a), Let n = lip/*,
where the p's are distinct primes, and let c be a divisor of n and a multiple
of pi°'. If a, j3 are relatively prime, the g. c. d. of 5 = a"^^'— iS'*''^' and
Qc{a, /3) is 1 or pi and at most one Qda, /3) contains the factor pi when
d contains pi^; if pi>2 divides 5, at most one Qcio-, jS) contains pi, and no
one of them contains pi^. If a, /3 are relatively prime and c = mpi"', where
m>l and m is prime to pi, then QXcl, jS) is divisible by pi if and only if
fjx—j^x ^jj^Q^ p^) holds for x = m, but not for 0<a;<m; in all other cases
Q= 1 (mod m). If a, jS are relatively prime, QXo-, jS), and hence also a"—^",
has a prime factor not dividing a*— j3'(s<c), except in the cases (i) c = 2,
^ = 1^ a = 2^-l; (ii) Q,(a, /3) =p = greatest prime factor of c, and a"^^=/3"/^
(modp); (iii)a(a,/3) = l.

E. Miot^^ noted that LeLasseur's^^ formula is the case m = n = l of

/02fc+1^2\ 2 / 02t+1^2 \

(f_JL) +^2^n(m+^-^±2*+in
\ m / \ m I

Welsch (p. 213) stated that the latter is no more general than the case A: = 0,
which follows from the known formula for the product of two sums of two
squares.

A. Cunningham^^ noted the decomposition into primes :

2"+l = 3-43-617-683-78233-35532364099.

"L'interm^diaire des math., 1906, 87; 1908, 135; 18, 1911, 200. Cf. Dickson."

'"Amer. Math. Monthly, 14, 1907, 8-9.

'i76id., 13, 1906, 155-6.

"Report British Assoc, 78, 1908, 615-6.

"Proc. Edinburgh Math. Soc, 26, 1908, 67-86; corrections, 28, 1909-10, viii.

"aJour. Indian Math. Club, 1, 1909, 212.

'^Messenger Math., 38, 1908, 14-32, and Dickson"*"' of Ch. XIV.

'^Amer. Math. Monthly, 16, 1909, 153-9.

'«L'interm6diaire des math., 17, 1910, 102.

"Report British Assoc, for 1910, 529; Proc. London Math. Soc, (2), 8, 1910, xiii.

390 History of the Theory of Numbers. [Chap, xvi

A. Cunningham"^ discussed quasi-Mersenne numbers N'g = x^—y^, with
x — y=l, q a prime, tabulating every prime factor < 1000 for q<50, a:<20
if q>o, a:<50 if q = 5, and treated Aurifeuillians

{X''=^Y')/{X=^Y), X = ^^, Y = qy]\

H. C. Pocklington"^ proved that, if n is prime, (x" — ?/'*)/(x — ?/) is divisible
only by numbers of the form 77m + 1 unless x — y\s, divisible by n [Euler],
and then is divisible only by n and numbers of the forms mn-\-\, n{inn-\-\).

G. Fonten^*° stated that, if p is a prime and x, y are relatively prime,
each prime factor of {x^ — y^)/{x — y) is of the form A'p + 1, except for a
factor p, occurring if x=y (mod p) and then only to the first power if p>2.

G. Fonten^^^ considered the homogeneous form/t(x, y) derived from (1)
by setting a = x/y. If p" is the highest power of a prime p dividing n.

The main theorem proved is the following: If x, y are relatively prime
every prime divisor of /„(x, y) is of the form kn+l, unless it is divisible by
the greatest prime factor (say p) of n. It has this factor p if p — 1 is divisible
by n/p°- and if x, y satisfy /„/pa=0 (mod p), the latter having for each y prime
to p a number of roots x equal to the degree of the congruence. In par-
ticular, if n is a power of a prime p, every prime factor of /„ is of the form
kn-\-l, with the exception of a divisor p occurring if x=y (mod p), and then
to the first power if n5^2.

J. G. van der Corput^^ considered the properties of the factors of the
expression derived from a' +6' as (1) is derived from a' — 1.

A. G^rardin^ factored a^+6^ in four numerical cases and gave
(a2+3iS2)H(4ai3)*=n{(3a2=fc2ai3+3/32)2-2(2a2±2a/3)2).

A. Cunningham^ tabulated factors of y'^^2, 2?/*± 1.

R. D. CarmichaeP^ treated at length the numerical factors of a"=tj8"
and the homogeneous form Qnio-, /3) of (1), when a+^S and a/5 are relatively
prime integers, while a, j8 may be irrational.

A. G^rardin^S'^ factored xHl for x = 373, 404, 447, 508, 804, 929; inves-
tigated x'* -2 for x^ 50, y^-Sfory^ 75, Sv^ - 1 for y^ 25, 2w^ -Iforw^ 37,
and gave ten methods of factoring numbers Xa^ — 1.

L. Valroff^^'' factored 2x^-1 for 101^x^180, 8x^-1 for x<128.

A. Gerardin^^*^ expressed 622833161 (a factor of 20^°+ 1) as a sum of two
squares in two ways to get its prime factors 2801 and 222361.

"Messenger Math., 41, 1911-12, 119-145.

"Proc. Cambr. Phil. Soc, 16, 1911, 8.

'"Nouv. Ann. Math., (4), 9, 1909, 384; proof, (4), 10, 1910, 475; 13, 1913, 383-4.

"Ubid., (4), 12, 1912, 241-260.

8«Nieuw Archicf voor Wiskunde, (2), 10, 1913, 357-361.

"Wiskundig Tijdschrift, 10, 1913, 59.

"Messenger Math., 43, 1913-4, 34-57.

«Annals of Math., (2), 15, 1913-4, 30-70.

w^Sphinx-Oedipe, 1912, 188-9; 1913, 34-44; 1914, 20, 23-8, 34-7, 48.

o^^lbid., 1914, 5-6, 18-9, 28-30, 33, 37, 73.

*^Ibid., 39. Stated by E. Fauquembergue, I'interm^diaire des math., 21, 1914, 45.

I

Chap. XVI] FACTORS OF a** ±6". 391

A. Cunningham^Habulated factors of y^=^l,x'^=^y''", and gave an account
of printed and manuscript tables of solutions of 2/"*='=l = 0 (mod p^).

Cunningham^^ tabulated factors of x^^^y"" for x^lQ and certain y's as
high as 31 when x = 2 or 4, where x, y are relatively prime and x> 1, y> 1.

Cunningham^^ noted that x-2''+l is composite for l<a;<233, x 9^ 14:1.

A. Cunningham and H. J. WoodalP^ tabulated factors of 2'^^q and
g.2*±l for 5-^66, and tabulated values of q for which one of these four
functions is divisible by a given prime p or power of p. They confirmed
that X.2'' + 1 is composite when 1< x< 233 except perhaps when x = 141 . In-
cidentally (p. 15), the factors of 2*"^^; — 1 for A; ^ 17 are given.

For factors of 2^ — 1 and 10" — 1, see Chapters I and VI. For factor
tables of numbers m.2^±l, see Seelhoff^^ ^^^ Morehead^o of Ch. XIII; for
m. 6^=1=1, Dines^^ For factors of several numbers d^ — 1, see Lawrence^^,
Biddle^^ and Kraitchik^i of Ch. XIV. For the form of factors of a'^+b"
when k = 2^, see Euler" of Ch. XV. Various results in Ch. XVII relate to
factors of a'*=t5'».

Factors of Trinomials.

Seven^^ primes p such that (p^ — 1)^ has 4 or more factors px+l,x<p.
List^^ of algebraically factorable trinomials x^+xy'^+y^, etc.
Factors" of 14^14^+1, 7^+2-7'+l, etc.

Conditions that x^-\-Px'^-\-c^ be a product of 4 rational quadratic factors.^^
Two^^ factors of x^-{-i4:m'^+Sm^+2)xY+y\
Factors^"*^ of various trinomial expressions.

For factors of x'^+Qbx^+b^ see Dirichlet^ of Ch. XVII. See papers 28,
28a, 65, 89 above.

8«Messenger Math., 45, 1915, 49-75.

^Ubid., 185-192.

ssProc. London Math. Soc, (2), 4, 1907, xviii; (2), 15, 1916-7, xxix.

s^Messenger Math., 47, 1917, 1-38. Math. Quest. Educ. Times, (2), 10, 1906, 44.

»5Math. Quest. Educat. Times, (2), 15, 1909, 82-3. Amer. Math. Monthly, 15, 1908, 67, 138.

L'intermediaire des math., 15, 1908, 121.
9«Math. Quest. Educ. Times, (2), 16, 1909, 39-41.
»Ubid., 65-6.

«8/6id., (2), 18, 1910, 64-5; (2), 22, 1912, 20-1.
s^Sphinx-Oedipe, 6, 1911, 8-9.
""Math. Quest. Educ. Times, 72, 1900, 26-8; 74, 1901, 130-1; (2), 6, 1904, 97; 19, 1911, 85;

20, 1911, 25-6, 76-8; 22, 1912, 54-61. Math. Quest, and Solutions, 3, 1917, 66; 4, 1917,

13,39; 5, 1918, 38, 50-1.

CHAPTER XVII.

RECURRING SERIES; LUCAS* Un, Vn.

Leonardo Pisano\ or Fibonacci, employed, in 1202 (revised manuscript,
1228), the recurring series 1, 2, 3, 5, 8, 13, ... in a problem on the number of
offspring of a pair of rabbits. We shall write Un for the nth term, and Un
for the {n-\-l)th term of 0, 1, 1, 2, 3, 5, . . . derived by prefixing 0, 1 to the
former series.

Albert Girard^ noted the law w„+2 = ^<n+i+'Wn for these series.

Robert Simson^ noted that this series is given by the successive conver-
gents to the continued fraction for (\/5 + l)/2. The square of any term is
proved to differ from the product of the two adjacent terms by =*= 1.

L. Euler^ noted that {a-\-\/b)'' = Ak+Bk^ implies

A, = h{{a-\-Vbr+ia-Vbr}, B, = -~^{ia+Vbr-{a-Vby].

J. L. Lagrange^ noted that the residues of Ak and B^ with respect to any
modulus are periodic.

Lagrange^ proved that if the prime p divides no number of the form
f—au^, then p divides a number of the form

{{t-huVar+'-it-uV^)^']/Va.

A. M. Legendre' proved that, if (f)^—A^^ = l, then ((l>+\l/VAy — l is
of the form r+sV^? where r and s are divisible by a prime w, not dividing

8=<o-lit(i) = +l, «=«+litg) = -l.

C. F. Gauss* proved [Lagrange's^ result] that, if 6 is a quadratic non-
residue of the prime p, then Bp+i is divisible by p for every integral value
of a. If e is a divisor of p+ 1, then Be is divisible by p for e — 1 values of a,
being a factor of B^+i.

G. L. Dirichlet^ proved that, if b is an integer not a square and x is any
integer prime to b, and if U, V are polynomials in x, b such that

{x+Vbr=^u-\-vvb,

then U and V have no common odd divisors. If n is an odd prime, no prime
of which 6 is a quadratic residue is a factor of V unless it be of the form
2mn+l. No prime of which 6 is a quadratic non-residue is a factor of V
unless it be of the form 2mn — l. Lagrange^ had proved conversely that a

iScritti, I, 1857 (Liber Abbaci), 283-4.

^L'Arithm^tique de Simon Stevin de Bruges, par Albert Girard, Leyde, 1634, p. 677. Lea

Oeuvres Math, de Simon Stevin, 1634, p. 169.
3Phil. Trans. Roy. Soc. London, 48, I, 1753, 368-376; abridged edition, 10, 1809, 430-4.
*Novi Comm. Acad. Petrop., 18, 1773, 185; Comm. Arith., 1, 554.

^Additions to Euler's Algebra, 2, 1774, §§ 78-9, pp. 599-607. Euler, Opera Omnia, (1), 1, 619.
•Nouv. M^m. Ac. Berlin, ann^e 1775 (1777), 343; Oeuvres, 3, 782-3.

'TWorie des nombres, 1798, p. 457; ed. 2, 1808, p. 429; ed. 3, 1830, vol. 2, Art. 443, pp. 111-2.
«Disq. Arith., 1801, Art. 123. »Deformishnearibus,Breslau,1827; Werke, 1,51. Cf . Kronecker."

393

394 History of the Theory of Numbers. [Chap, xvn

prime of which 6 is a non-residue, and having the form 2mn — 1, vdW di\'ide V.
li b= —n, where n is a prime 4m-\-3, no prime divides V unless it is of the
form A-n=fc 1, and conversely. The divisors of U are discussed for the case
n a power of 2; in particular, of U = x^+Qbx^-\-b^ when n = 4.

J. P. M. Binet^° noted that the number of terms of a solution t'„, expressed
as a function of n, ro, . . ., of the equation t'„+2 = i'„+i+''«i'n in finite differ-
ences is

^(i^-'-(^)-*')-

This equals f/„ as shown by taking each r„ to be unity.

G. Lam6^^ used the series of Pisano^ to prove that the number of divi-
sions necessary to find the g. c. d. of two integers by the usual process of
division does not exceed five times the number of digits in the smaller
integer. Lionnet^- added that the number of divisions does not exceed three
times it when no remainder exceeds half the corresponding di\'isor. See
also Serret, Traits d'Arithmetique; C. J. D. Hill, Acta Univ. Lundensis,
2, 1865, No. 1; E. Lucas, Nouv. Corresp. Math., 2, 1876, 202, 214; 4,
1878, 65, and Th^orie des Nombres, 1891, 335, Ex. 3; P. Bachmann, Niedere
Zahlentheorie, 1902, 116-8; L. Grosschmid, Math.-Naturwiss. Blatter, 8,
1911, 125-7, for an elementary proof by induction; Math, es Phys. Lapok,
23, 1914, 5-9; R. D. Carmichael, Theory of Numbers, p. 24, Ex. 2.

H. Siebeck^^ considered the recurring series defined by

for a, c relatively prime. By induction,

where /3 = 0 or 1, 7 = (r — 1)/2 or (r — 2)/2, according as r is odd or even;

whence A^^ is divisible by N^- If P and q are relatively prime, Np and
A"g are relatively prime and conversely. If p is a prime, 6 = a"+4c, and
s = (b/p) is Legendre's symbol, then

Np=s, Np.,= 0 (mod p),

so that either Np+i or A"p_i is divisible by p.

J. Dienger^^ considered the question of the number of terms of the series
of Pisano with the same number of digits and the problem to find the rank
of a given term.

A. Genocchi^^ took a and b to be relatively prime integers and proved
that B„„ is divisible by B„ and that the quotient Q has no odd divisor in

"Comptea Rendus Paris, 17, 1843, 563.

"Ibid., 19, 1S44, 867-9. Cf. Binet, pp. 937-9.

'*Compl^ment des 616ments d'arithm^tique, 1857, 39-42.

"Jour, fur Math., 33, 1846, 71-6. "Archiv Math. Phys., 16, 1851, 120-4.

"AnnaU di Mat., (2), 2, 1868-9, 256-267. Cf. Genocchi". ".

Chap. XVII] Recueeing Seeies; Lucas' Un, v^. 395

common with B^ other than a divisor of n. If p is an odd divisor of B^^ and
if h is the least k for which B^ is divisible by p, then /i is a divisor of m. If p
is an odd prime, Bp_i or Bp^i is divisible by p according as 6 is a quadratic
residue or non-residue of p, whatever be the value of a. This is used to
prove the existence of primes of the two forms n'2;±l(n a prime >2) and
the existence of an infinitude of primes of each of the forms mz^l [Ch . XVIII] .
E. Lucas^^ stated without proof theorems on the series of Pisano.^ The
sum of the first n terms equals C/„+2 — 2; the sum of those terms taken with
alternate signs equals ( — l)"C/„_i. Also

U „_i -\-U n— U2n, UnUn+l ~ U n—\ U n—2 = U 2n} U n'^U n+1 ~ U „_i = C/ 3„+2'

We have the symbolic formulas

where, after expansion, exponents are replaced by subscripts. From
E. Catalan's Manuel des Candidats a I'Ecole Polytechnique, I, 1857, 86, he
quoted

Lucas^'^ employed the roots a,boix^ = x-\-l and set

^ ^ n \ 1.71 ^2re I

a — 0 Un

The u's form the series of Pisano with the terms 0, 1 prefixed, so that
Uo=0, Ui = U2=l, U3 = 2. Since 5w„^ — z^„^ = ± 4, u^ and Vn have no common
factor other than 2. If p is a prime ^2, 5, we have Up=±l, Vp = l (mod
p). We have the symbolic formulas

Given a law Un+k = -^oUn+p+ ■ ■ ■ -i-ApUn of recurrence, we can replace the
symbol f/* by 0 ( C/) , where

(f){u)=Aou''+Aiu''-^+. . . +Ap_^u+A

p)

since U^+kp^ U''{({){U)}^, symbolically.

E. Lucas^^ stated theorems on the series of Pisano. We have

2"\/5i/, = (l + V5r-(l-V5r, ^n+i = l + (i) + (''2^) + ---

and his^^ symbolic formulas with u's in place of U^s. Up^ is divisible by Up
and Uq, and by their product if p, q are relatively prime. Set Vn = U2n/un.
Then

Vn+2 = Vn+l+Vn, Vin = An-2, y4„+2 = «^Wl +2-

«Nouv. Corresp. Math., 2, 1876, 74r-5.

^Ubid., 201-6.

"Comptes Rendus Paris, 82, 1876, 165-7.

396 History of the Theory of Numbers. [Chap, xvii

If the term of rank ^ + 1 in Pisano's series is divisible by the odd number A
of the form 10^=*= 3 and if no term whose rank is a divisor of A + 1 is divisible
by .4 , then A is a prime. If the term of rank A — 1 is divisible by A = 10p=t 1
and if no term of rank a divisor of A — 1 is divisible by A, then A is a prime.
It is stated that A=2^^^ — 1 is a prime since A = 10p — 3 and u^ is never
divisible by A for k = 2", except for n = 127.

Lucas^^ employed the roots a, 6 of a quadratic equation x^— Px+Q = 0,
where P, Q are- relatively prime integers. Set

a" — 6"

Un = r-' Vn = a"+h'*, 5 = o — 6.

a — o

The quotients of 5if„ V — 1 and y„ by 2^"^^ are functions analogous to the
sine and cosine. It is stated that

(1) U2n = UnVn, V^-bW = '^Q',

(2) 2u^+ri = UmVn + U„Vm, "J^n^ " Itn-l^^n+l = Q'*"^

Not counting divisors of Q or 5^, we have the theorems:

(I) Wpg is divisible by Up, u^, and by their product if p, q are relatively
prime.

(II) Un, Vn are relatively prime.

(III) If d is the g. c. d. of m, n, then Ud is the g. c. d of u^, Un.

(IV) For n odd, u^, is a divisor of x^ — Qif'.

By developing w„p and f„p in powers of Un and v„, we get formulas analo-
gous to those for sin nx and cos nx in terms of sin n and cos n, and thus get
the law of apparition of primes in the recurring series of the it„ [stated
explicitly in Lucas"*^], given by Fermat when 5 is rational and by Lagrange
when 5 is irrational. The developments of uj' and v^^ as linear functions of
""nj '^2n, ■ ■ ■ are like the formulas of de Moivre and Bernoulli for sin^x and
cos^x in terms of sin kx, cos kx. Thus —

(V) If n is the rank of the first term u^ containing the prime factor p
to the power X, then Uj^ is the first term divisible by p^"*"^ and not by p^"*"^;
this is called the law of repetition of primes in the recurring series of w„.

(VI) If p is a prime 4g+l or 4g+3, the divisors of u^Ju^ are divisors
of x^—py^ or S^x^+pi/^, respectively.

(VII) If Up^i is divisible by p, but no term of rank a divisor of p=*=l is
divisible by p, then p is a prime.

Lucas^*^ proved the theorems stated in the preceding paper. Theorems
II and IV follow from (I2) and (22), while (20 shows that every factor
common to w^^.„ and u^ divides Un and conversely.

(VIII) If a and h are irrational, but real, t^p+i or Wp_i is divisible by the
prime p, according as 6^ is a quadratic non-residue or residue of p (law of
apparition of primes in the it's). If a and h are integers, Up^i is divisible
by p. Hence the proper divisors of u^ are of the form /en +1 if 6 is rational,
/cn=*=l if 5 is irrational.

"Comptes Rendus Paris, 82, 1876, pp. 1303-5.

"Sur la thdorie des nombres premiers, Atti R. Accad. Sc. Torino (Math.), 11, 1875-6, 928-937.

Chap. XVII] RECURRING SERIES ; LuCAS' Un, V^. 397

The law V of repetition of primes follows from

where t = (p — l)/2. Special cases of the law are due to Arndt,^^ p. 260,
and Sancery,^^ each quoted in Ch. VII. Theorem VII, which follows from
VIII, gives a test for the primality of 2"± 1 which rests on the success of
the operation, whereas Euler's test for 2^^ — 1 was based on the failure of
the operation. The work to prove that 2^^ — 1 is prime is given, and it is
stated that 2^'' — 1 was tested and found composite, ^^ contrary to Mersenne.
Finally, a^+Qy^ is shown to have an infinitude of prime divisors.

A. Genocchi^^ noted that Lucas' w„, y„ are analogous to his^^ 5„, A^.
[If we set a = a+\/b, ^ = a — \/h, we have

a — p

Lucas^^ stated that, if 4m+3 is prime, p = 2*'"+^ — 1 is prime if the first
term of the series 3, 7, 47,. . ., defined by r„_,.i = r„^ — 2, which is divisible
by p is of rank 4m+2; but p is composite if no one of the first 4m +2 terms
is divisible by p. Finally, if a is the rank of the first term divisible by p,
the divisors of p are of the form 2"A;=t:l, together with the divisors of
x^ — 2y^. There are analogous tests by recurring series for the primality of

3.24m+3_i^ 2-3*™+2±i^ 2-3*'"+^-l, 2-52'"+' + l.

Lucas^^ proposed as an exercise the determination of the last digit in the
general term of the series of Pisano and for the series defined by w„+2
= aUn+i-\-bUn', also the proof of VIII: If p is a prime,

(a-\-Vby-^-(a-Vby-'^

Up^l—-

Vb

is divisible by p if 6 is a quadratic residue of p, excepting values of a for
which a^ — 6 is divisible by p; and the corresponding result [of Lagrange^ and
Gauss^] for Up+i. Moret-Blanc^^ gave a proof by use of the binomial theorem
and omission of multiples of p.

Lucas^^ wrote s„ for the sum of the nth powers of the roots of an
equation whose coefficients are integers, the leading one being unity.
Then Snp — sJ' is an integral multiple of p. Take n = 1. Then Si = 0 impHes
Sp= 0 (mod p) . It is stated that if Si = 0 and if Sj, is divisible by p for k = p,
but not for k<p, then p is a prime.

*iA. Cunningham, Proc. Lond. Math. Soc, 27, 1895-6, 54, remarked that, while primality is
proved by Lucas' process by the success of the procedure, his verification that a number
is composite is indirect and proved by the failure of the process and hence is liable to error.

22Atti. R. Accad. Sc. Torino, 11, 1875-6, 924.

^Comptes Rendus Paris, 83, 1876, 1286-8.

2*Nouv. Ann. Math., (2), 15, 1876, 82.

^mid., (2), 20, 1881, 258 [p. 263, for primality of 2"-l].

28Assoc. frang. avanc. sc, 5, 1876, 61-67. Cf. Lucas^*.

398 History of the Theory of Numbers. (Chap, xvii

By use of (1) and (2), theorems I-IV are proved. Theorem VIII is
stated, and VII is proved. Employing two diagrams and working to base 2,
he showed that 2"^^ — 1 is a prime.

Lucas" considered a product m = p^i* ... of powers of primes, no one
dividing Q. Set A = (a-6)^ (A/p)=0, ^\=^^r>-l)/2 ^^^^ ^^^

[51?

,W=."-V-...[p-g)][.-(f)]

Then w<=0 (mod m) for f =^(w). The ranks n of terms u^ divisible by m
are multiples of a certain divisor /z o{\p{m). This ii is the exponent to which
a or 6 belongs modulo vi. The case 6 = 1 gives Euler's generalization of
Fermat's theorem. The primality test^^ is reproduced and applied to show
that 2^^ — 1 is a prime.

Lucas^^ considered the series of Pisano. Taking a, 6 = (l=tv5)/2, we
have Ml =1*2 = 1, 1*3 = 2, etc. According as n is odd or even the divisors of
u-iJun are divisors of 5x^ — 3?/^ or 5a:^+32/"; those of u^Ju2n are divisors of
5x^ — 2zf or 5x^'-f-2?/^; those of v^Jvn are divisors of x^+Sy^ or x^ — 3y^; those
of V2n are divisors of x^+22/^ or x^ — 2y^; those of u^JUn are divisors of x^+Sy^
or T' — hy^. The law V of repetition of primes and theorem III are stated.
The law VIII of apparition of primes now takes the following form: If p is a
' prime 10g=t 1, Wp_iis divisible by p ; if p is a prime lOg^ 3, i/p+i is divisible by p.
The test^^ for the primality of A is given and applied to show that 2^^^ — 1
and 2^^ — 1 are primes. There is a table of prime factors of u^ for n^60.

L Finally, ^u^ju^ is expressible in the form x^ — 'py^ or bx^+py"^ according as
the prime p is of the form 45-+! or 40^+3.

Lucas^^ considered the series defined by r„+i = r„^ — 2,

Let A = 3or9 (mod 10), g=0 (mod 4) ; or A = 7, 9 (mod 10), g=l( mod 4);
or A=l, 7 (mod 10), g=2 (mod 4); or A=l, 3 (mod 10), q=S (mod 4).
Then p = 2'A — 1 is a prime if the rank of the first term divisible by p is 5 ;
if a {a<q) is the rank of the first term divisible by p, the divisors of p are
either of the form* 2aAk-{-l, or of the forms of the divisors of x^ — 2y^
and x^ — 2Ay'^. Corresponding tests are given for 2^ A -\- 1 and S'^A — 1. The
first part of the theorem of Pepin^'^ for testing the primaUty of a„ = 2^"+l
follows from theorem VII with a = 5, 5 = 1, p = a„; the second part follows
from the reciprocity theorem and the form of a„ — 1 .

For A=p, let the above rj become r. When p=7 or 9 (mod 10) and
p is a prime, then 2p — 1 is a prime if and only if r=0 (mod 2p — 1). When
p = 4g+3 is a prime, 2pH-l is a prime if and only if 2''=1 (mod 2p + l).
When p = 4^-4- 3 is a prime, 2p — 1 is a prime if and only if

*'Comptes Rendus Paris, 84, 1877, 439-442. Corrected by Carmichael.*'

"Bull. Bibl. Storia Sc. Mat. e Fis., 10, 1877, 129-170. Reprinted as " Recherches sur plusieura

ouvrages de Leonard de Pise." Cf . von Sterneck" of Ch. XIX.
"Assoc, frang. avanc. sc, 6, 1877, 1.59-166. *Corrected to 2MA'=tl in Lucas"; see Lucas."
'"KUomptes Rendus Paris, 85, 1877, 329-331. See Ch. XV, Pepin", Lucas,"' " Proth.^^

Chap. XVII] RECURRING SERIES ; LuCAS' W„, V^. 399

:^{a+V2y-a-V2r}^o (mod2p-i).

To_test the primality of p = 2^^^^ — l, use x^ — 4x-{-l=0 with the roots
2± Vs. Then if p is a prime, Wp+i is divisible by p. We use the residues
of the series 2, 7, 97, . . . defined by r„+i = 2r„^ — 1.

Lucas^^ stated that p = 2'^'""*"^ — 1 is a prime if the rank of the first term^^
of 3, 7, 47, . . . divisible by p is between 2m and 4m +2. To test P = 2^«+^ - 1,
form the series

ri = l, r2=-l, rs=-7, r, = 17,..., r„+i = 2r„2-32"-';

if ^ is the least integer for which r^ is divisible by P, then P is a prime when I
is comprised between 2g and 4g+l, composite when ?>4g' + l.

Lucas^^ expressed Un, v^ as polynomials in P and A = P^ — 4Q = 5^, obtained
various relations between them corresponding to relations between sine and
cosine; in particular,

Wn+2 — P'^n+l ~ Q'^ni '^n+2r — ^r'^n+r ~ Q ^n>

and formulas derived from them by replacing uhy v; also symbolic formulas
generalizing those^^ for the series of Pisano.

In the second paper, Un+i, v^ are expressed as determinants of order n
whose elements are Q, — P, 2, 1, 0. There is given a continued fraction for
U(n+i)r/unr, hoTCi whlch Is derfved (I2) and generalizations. The same
fraction is developed into a series of fractions.

Lucas^^ noted that u^r is divisible by Ur since

where ^ = Jn — 1 if n is even, f = J(n — 1) if n is odd, the final factor being then
absent. Proof is given for (2i) and 2y^+„ = ?;^y„+AM„w^. From these are
derived new formulas by changing the sign of n and applying

To show that

[m, n\ = —

is integral, apply (2i) repeatedly to get

2[m, n\ = [m — l, n]Vn+{m, n — \]v^.

Finally, sums of squares of functions Un, v^ are found.

Lucas^^ gave a table of the linear forms 4A+?' of the odd divisors of
x^-\-Llf and x^—I\'if' for A = l,. . ., 30. By use of (I2), it is shown that the
terms of odd rank in the series u^ are divisors of x^ — Qif' ; the terms of even or
odd rank in the series v^ are divisors of x^+A?/^ or x^-\-QAy^, respectively.

3iMessenger Math., 7, 1877-8, 186.

'^Sur la theorie des fonctions numeriques simplement p^riodiques, Nouv. Corresp. Math., 3,
1877, 369-376, 401-7. These and the following five papers were reproduced by Lucas.'*
^Hhid., 4, 1878, 1-8, continuation of preceding.
^'lUd., pp. 33-40.

400 History of the Theory of Numbers. [Chap, xvii

Lucas^^ proved III by use of (2i) and gave

Lucas^^ determined the quadratic forms of divisors of i'2n from
t;2n=Aw„2+2Q", V2n = vJ'-2Q\

In the last, take Q = 2f, n = 2/1+1; thus 1^4^+2 factors if Q is the double of a
square. As a special case we have the result by H. LeLasseur (p. 86) :

In the first expression for t'2n, take n=juH-l, A = ±2/i^, Q==r^ff^; thus
Vi^+2 factors when QA is of the form — 2f. Similarly, v^^ factors if A = —2f.
Lucas" gave the formulas

developments of w„^, t'/ as linear functions of Vkn, k = p, p — 2, p — i,. . ., and
complicated developments of w„r, ^nr-

Lucas^^ reproduced the preceding series of seven papers, added (p. 228)
a theorem on the expression of 4Upr/ur as a quadratic form, a proof (p. 231)
of his^^ test for primality by use of the s^, and results on primes and perfect
numbers cited elsewhere.

Lucas^^ considered series w„ of the first kind (in which the roots a, h are
relatively prime integers) and deduced Fermat's theorem and the analogue
it<=0 (mod m), t = 4>(m), of Euler's generalization. Proof is given of the
earlier theorems VII, VIII and (p. 300) of his" generalization of the Euler-
Fermat theorem. The primality test^^ is stated (p. 305) and applied to
show that 2^^ — 1 and 2^^ — 1 are primes. It is stated (page 309) that
p = 2'**+^ — 1 is prime if and only if

3=2coS7r/22«+i (mod p),

after rationalizing with respect to the radicals in the value of the cosine.
The primality tests^^ are given (page 310), with similar ones for 3'yl + l,
2-5'A + l. The tests^^ for the primaUty of 2p + l are given (p. 314). The
primality test^^ for 2'^'''^^ — 1 is proved (pp. 315-6).

Lucas"*" reproduced his^^ earlier results, and for p = 3, 5, 7, 11, 13, 17,
expressed ypr/i'2r in the form x^— 2pQV> and, for p a prime ^31, expressed

»»Nouv. Corresp. Math., 4, 1878, 65-71.

"Ihid., pp. 97-102.

*Ubid., pp. 129-134, 225-8.

»«Amer. Jour. Math., 1, 1878, 184-220. Errors noted by Carmichael."

"Ibid., pp. 289-321.

"Atti R. Accad. Sc. Torino, 13, 1877-8, 271-284.

Chap. XVII] RECURRING SeRIES; LucAS' U„, y„. 401

Upr/Ur in the form Ax^^pQ''y'^. The prime factors of 3^^±1 are given on
p. 280. The proper divisors of 2^"+l are known to be of the form Snq-\-l;
it is shown that q is even. Thus for 2^^+l the first divisor to be tried is
641, for 2^^^+! the first one is 114689; in each case the division is exact
(cf. Ch. XV). The following is a generalization: If the product of two I
relatively prime integers a and h is of the form 4/i+l, the proper divisors
of a^'^^^+b^"^'^ are of the form Sahnq+1. A primality test for 2'^^+^-! isj
given. Finally, p = 2^"^^+^"+^ — 1 is a prime if and only if

(2"+V2^^)^+(2"-V2^H4)^ = 0 (mod p).
T. Pepin* ^ gave a test for the primality of g = 2" — 1. Let

^1- ^2-1-52 (modg')
and form the series Ui, U2y. . ., it„_i by use of

u^+i=u^ — 2 (mod q).

Then g is a prime if and only if u^-i is divisible by q. This test differs from
that by Lucas^^ in the choice of Ui.

E. Lucas"*^ reproduced his^^ test for the primality of 2^ A — 1, etc., and the
test at the end of another paper,*" with similar tests for 2*'^+^ — 1 and 2^^*'+^ — 1 .

G. de Longchamps*^ noted that, if dk = Uk — aUk-i,

d, = h''-\ d^d, = ¥+^-\

with the generalization

X

Jldj,.=d„ s = pi+. . .+p^-x+l.
Take pi = . . . = p^; = p. Hence

[Up CLUp^i) =Upx—x+l f^Upx—x'

There is a corresponding theorem for the v's.

J. J. Sylvester** considered the g. c. d. of u^, u^+i if

w^ = {2x - l)Ux-i - {x-l)u^_2'

E. Gelin*^ stated and E. Cesaro*^ proved by use of ?7„+p= UpUn+ C/p_iC/„_i
that, in the series of Pisano, the product of the means of four consecutive
terms differs from the product of the extremes by ± 1 ; the fourth power of
the middle term of five consecutive terms differs from the product of the
other four terms by unity.

"Comptes Rendus Paris, 86, 1878, 307-310.

«Bull. Bibl. Storia Sc. Mat. e Fis., 11, 1878, 783-798. The further results are cited in Ch. XVI.

Comptes Rendus, 90, 1880, 855-6, reprinted in Sphinx-Oedipe, 5, 1910, 60-1.
«Nouv. Corresp. Math., 4, 1878, 85; errata, p. 128.
«Comptes Rendus Paris, 88, 1879, 1297; Coll. Papers, 3, 252.
«Nouv. Corresp. Math., 6, 1880, 384.
"Ibid., 423-4.

402 History of the Theory of Numbers. [Chap, xvii

Magnon,'*^ in reply to Lucas, proved that

) Oi Oj Og ■ ■ ■ 1 — V5

I if a„ — 1 is the sum of the squares of the first n — 1 terms of Pisano's series.

H. Brocard^^ studied the arithmetical properties of the U's defined by
Un+i = Un-\-2U„_i, Uo = l, Ui=3, in connection with the nth pedal triangle.

E. Ces^ro^^ noted that if Un is the nth term of Pisano's series, then
(2C/+l)"-C/^'* = 0, symbolically.

E. Lucas^" gave his^^ test for the primahty of 2'*^+^ — !.

A. Genocchi" reproduced his^^ results.

M. d'Ocagne^^ proved for Pisano's series that [Lucas^®]

iu, = u^2-h 2)(-iyii,= (-l)X-i-l, lim-^=(i±^',

»=0 P=« (*p-i \ Z /

The main problem treated is that to insert p terms ai, . . ., ap between two
given numbers ao = a, ap+i = h, such that aj = a;_i+a,_2. The solution is

hUi-{-{ — iyaUp+i.i

Up+i

Most of the paper is devoted to the question of the maximum number of
negative terms in the series of a's.

E. Catalan^2apj.Q^3^ ^^^^ uji^Ur,-pU,+p= (-iy-'^^U\_i for Pisano's
series.

E. Lucas^^ stated, apropos of sums of squares, that

L. Kronecker^^ obtained Dirichlet's^ theorems by use of modular systems.
Lucas^" proved that, if w„=(a''— 5")/(a — 6),

Wp_l —U(p_i)n/Un

is divisible by Up when p is a prime and n is odd and not divisible by p, and
by Up when n = 2p+l.

L. Liebetruth^^ considered the series Pi = 1 , P2 = x, . . . , P^ = ^Pn-i —Pn-2)
and proved any two consecutive terms are relatively prime, and

Pn = PxPn-X+l-Px-lPn-X (X<n).

Taking n = 2X, 3X, . . . , we see that Px is a common factor of P2X, Psx, • • • •
The g. c. d. of P,„, P„ is Pj, where d is the g. c. d. of ?n, n. Next,

«'Nouv. Corresp. Math., 6, 1880, 418-420. '"Nouv. Corresp. Math., 6, 1880, 145-151.
"/bid., 528; Nouv. Ann. Math., (3), 2, 1883, 192; (3), 3, 1884, 533. Jornal de Sc. Math.

Astr., 6, 1885, 17.
»0R6cr6ation8 mathdmatiques, 2, 1883, 230. "Coraptes Rendus Paris, 98, 1884, 411-3.
"'Bull. Soc. Math. France, 14, 1885-6, 20-41.

^^M6m. soc. roy. sc. Li^ge, (2), 13, 1886, 319-21 ( = M61anges Math., II).
"Mathesis, 7, 1887, 207; proofs, 9, 1889, 234-5.

"Berlin Berichte, 1888, 417-423; Werke, 3, I, 281-292. Cf. Kronecker'" of Ch. XVI.
""Assoc. franQ. avanc. sc, 1888, II, 30. "Beitrag zur Zahlentheorie, Progr., Zerbst, 1888.

Chap. XVII] Recuering Series; Lucas' u^, y„. 403

P1+P3+ ■ . • +P2n-X=Pn\ P2 + -P4+ • • • +P2n = PnPn+l.

If P^=P^ (mod Px) then n=m (mod 2X). Also,

P„=x"-+ S (_i).(n-fe-l)...(n-2fc)^„.,,_,_
fc=i 1-2. . .A;

If a„/6„ is the nth convergent to i_j+^_..., then a„+2 = ^^n+i~cf„, 6„
= o„+i. Hence a^^Pn if cti = 1 , 02 = a;.

Sylvester stated and W. S. Foster^^" proved that if f{d) is a polynomial
with integral coefficients and Ux+i=f{Uj^, Ui=f{0), and 5 is the g. c. d. of
r, s, then Us is the g. c, d. of Ur, Ug.

A. Schonfiies^® considered the numbers no = l, Ui,..., n^ defined by
n^ = n^_n^-i+ri^-2_ . . . +(-1)^ (X = 0, 1,. . .)

and proved geometrically that if n^-i is the least of these numbers which
has a common factor with n^, then r is a divisor of g+1, while a relation

'mni=mnr+i (mod n^)
holds for every index i.

L. Gegenbauer^^ gave a purely arithmetical proof of this theorem.

E. Lucas^^ gave an exposition of his theory, with an introduction to
recurring series.

M. Frolov^^ used a table of quadratic residues of composite numbers to
factor Lucas' numbers v„.

D. F, Seliwanov^° proved Lucas' results on the factors of w„, ?;„.

E. Catalan^^ gave the first 43 terms of the series of Pisano, noted that
Un divides U2y,+i, that Uzn is a sum of two squares, and treated the series

Un = aun-i + w„-2, Ux = a, W2 = a^ + L

Fontes^^" proved theorems stated by Lucas^^ (p. 127), and found in an
elementary way the general term of Pisano's series, as given by Binet^^.
E. Maillet^^'' proved that a necessary condition that every positive
integer, exceeding a certain limit, shall equal (up to a limited number of
units) the sum of the absolute values of a finite number of terms of a recur-
ring series, satisfying an irreducible law of recurrence with integral coeffi-
cients, is that all the roots of the corresponding generating equation be roots
of unity.

W. ManteP^ noted that, if the denominator F{x) of the generating
fraction of a recurring series is irreducible modulo p, a prime, the residues
modulo p of the terms of the recurring series repeat periodically, and the
length of a period is at most p" — 1 ; the proof is by use of Galois' general-
ization of Fermat's theorem. The case of a reducible F{x) is also treated.

65<iMath. Quest. Educ. Times, 50, 1889, 54-5. ^«Math. Annalen, 35, 1890, 537.

"Denkschriften Ak. Wiss. Wien (Math.), 57, 1890, 528.

68Theorie des nombres, 1891, 299-336; 30; 127, ex. 1. A pamphlet, pubhshed privately by

Lucas in 1891, is cited in I'intermediaire des math., 5, 1898, 58.
"Assoc, frang. avanc. sc, 21, 1892, 149.
soMath. Soc. Moscow, 16, 1892, 469-482 (in Russian).
"Mem. Acad. R. Belgique, 45, 1883; 52, 1893-4, 11-14.

""Assoc, frang. avanc. sc, 1894, II, 217-221. "''Assoc, frang. avanc. sc, 1896, II, 78-89

•^Nieuw Archief voor Wiskunde, Amsterdam, 1, 1895, 172-184.

404 History of the Theory of Numbers. [Chap, xvii

R. W. D. Christie^ stated that, for the recurring series defined by
a„+i = 3a„ — a„_i, 27n — l is a prime if and only if a^ — 1 is di\'isible by
2m — 1. The error of this test was pointed out by E. B. Escott.^

S. R^alis"" noted that two of A'' consecutive terms of 7, 13, 25, . . .,
3(n^H-n)+7, . . . are di\'isible by iV if iV is a prime 6/^2 + 1.

C. E. Bickmore^** discussed factors of w„ in the final series of Catalan^\
He^" and others gave known formulas and properties of Pisano's series.

R. Perrin®^ employed r„ = r„_2 + r„_3, ro = 3, ^'l = 0, ?'2 = 2. Then v^ is
di\'isible by n if n is a prime. This was verified to be not true when n is
composite for a wide range of values of n. The same subject was considered
by E. jMalo^® and E. B. Escott®" who noted that Perrin's test is incomplete.

SeveraP^" discussed the computation of Pisano's w„ for large n's.

E. B. Escott"^ computed Sl/ti^. E. Landau^"' had evaluated Sl/wgA
in terms of the sum of Lambert's^ series of Ch. X, and "Zl/uoh+i in relation
to theta series.

A. Tagiuri^^ employed the series Wi = l, U2 = l, Us = 2,... of Leonardo
and the generalization Ui, U2,..., where t/„= t/„_i + i[7„_2, with Ui = a,
U2 = b both arbitrary. Writing e for a^+ab — h^, it is proved that

UJJ-Ur^.^U,^, = ( - 1)"- V^,+,_„e.

{C/„4.a+( — l)*?7„_j)/?7„ is an integer independent of a, h, n; it equals
Wj+i+Wj-i. It is shown that u^ is a multiple of u^ if and only if r is a
multiple of s.

Tagiuri^^ obtained analogous results for the series defined by Vn = hVn-i
-\-lVn-2, and the particular series r„ obtained by taking ri = l, V2 = h. If
h and I are relatively prime, v^ is a multiple of v^ if and only if r is a multiple
of s. Let ^{i\) be the number of terms of the series of f's which are ^ r, and
prime to it; if h>l, <i>(t',) is Euler's (f>{i); but, if h = l, <l>(r,) =0(^)+0(^y2),
the last term being zero if i is odd. If i and j are relatively prime, $(y,y)
=*(j'.)$(r;).

Tagiuri^" proved that, for his series of v's, the terms between v^p and
v^p+i) are incongruent modulo t'^. if h>l, and for /i = 1 except for Vkp+i=Vkp+2-
If /x is not divisible by k and e is the least solution of /-**=! (mod f*), then
Vj.= v^ (mod t';t) if a:=Ai (mod 4A:e).

If /x is not divisible by k, and k is odd, and €1 is the least positive solution of
P=l (mod Vk), then Vx=v^ (mod ft) if x=ij, (mod 2kei).
A. Emmerich^^ proved that, in the series of Pisano,

"Nature, 56, 1897, 10. «Math. Quest. Educat. Times, 3, 1903, 46; 4, 1903, 52

""Math. Quest. Educat. Times, 66, 1897, 82-3; cf. 72, 1900, 40, 71.

"*/6m/., 71, 1899,49-50. "«/6ui., Ill; 4, 1903, 107-8; 9, 1906, 55-7.

«L'interm6diaire des math., 6, 1899, 76-7.

*»Ibid., 7, 1900, 281, 312. "L'interm^diaire des math., 8, 1901, 63-64.

•'"/Wd., 7, 1900, 172-7. ^'>>Ibid., 9, 1902, 43-4.

•■<^BuU. Soc. Math. France, 27, 1899, 198-300. «'Periodico di Mat., 16, 1901, 1-12.

"Peridico di Mat., 97-114. "/bid., 17, 1902, 77-88, 119-127.

"Mathesis, (3), 1, 1901, 98-9.

Chap. XVII] Recuering Series; Lucas' t/„, v^. 405

Un+5=Un (mod 2), w„+5=3w„ (mod 5), ^n+6o=Wn (mod 10),

so that Uq, Us, Uq, Ug,. . . alone are even, Uq, %, u^q, . . . are multiples of 5.

J. Wasteels'^^ proved that two positive integers x, y, for which y^—xy—x^
equals +1 or — 1, are consecutive terms of the series of Pisano. If 5x^±4
is a square, a; is a term of the series of Pisano. These are converses of
theorems by Lucas. ^^

G. Candido^^ treated Un, v^, by algebra and function- theory.

E. B. Escott^^ proved the last result in Lucas' paper. ^°

A. Arista'^^ expressed S"if it~^ in finite form.

M. Cipolla'^^ gave extensive references and a collection of known formulas
and theorems on w„, v„. His apphcation to binomial congruences is given
under that topic.

G. Candido^^ gave the necessary and sufficient conditions, involving
the i/j, that a polynomial x has the factor x^ — Px-\-Q, whose roots are a, b.

A. Laparewicz'^^ treated the factoring of 2'"='= 1 by Lucas' method.^^

E. B. Escott^^" showed the connection between Pisano's series and the
puzzle to convert a square into a rectangle with one more (or fewer) units •
of area than the square.

E. B. Escott^^ applied Lucas' theory to the case it„ = 2tt„_i-f-w„_2.

L. E. Dickson'^^" proved that if Zj, is the sum of the kth powers of the roots
of a"'-]-pid^~^+ . . . +Pm = 0, where the p's are integers and pi = 0, then, in
the series defined by Zx+m-\-piZx+m-i+ • • • +PmZx = 0, Zt is divisible hy i\it is
a prime.

E. Landau^" proved theorems on the divisors of V^, Y^, where

{x^iT= VJx)^iYSx), i= \/^.
P. Bachmann^^ treated at length recurring series.
C. Ruggieri^^ used Pisano's series for w_„ to solve for ^ and r\

E. Zeuthen^^ proposed a problem on the series of Pisano. ^

H. Mathieu^^ noted that in 1, 3, 8, . . ., x,i+i = 3a:„— a:„_i, the expressions |
a^n^n+i + 1, Xn-iXn+i-\-l are squares. —

Valroff^^ stated in imperfect form theorems of Lucas.
A. Aubry^^ gave a summary of results by Genocchi^^ and Lucas.

"Mathesis, (3), 2, 1902, 60-62.

"Periodico di Mat., 17, 1902, 320-5; I'interm^diaire des math., 23, 1916, 175-6.
T*L'mterm6diaire des math., 10, 1903, 288. "Giornale di Mat., 42, 1904, 186-196.

"Rendiconto Ac. Sc. Fis. e Mat. Napoh, (3), 10, 1904, 135-150.
"Periodico di Mat., 20, 1905, 281-285.

"Wiadomosci Matematyczne, Warsaw, 11, 1907, 247-256 (Polish).

78oThe Open Court, August, 1907. Reproduced by W. F. White, A Scrap-Book of Elementary
Mathematics, Notes, Recreations, Essays, The Open Court Co., Chicago, 1908, 109-113.
"L'interm6diaire des math., 15, 1908, 248-9. "OAmer. Math. Monthly, 15, 1908, 209.

soHandbuch. . .Verteilung der Primzahlen, I, 1909, 442-5.

"Niedere Zahlentheorie, II, 1910, 55-96, 124. s^pgrjodico di Mat., 25, 1910, 266-276.

"Njrt Tidsskr. for Math., Kjobenhavn, A 22, 1911, 1-9. Solution by Fransen and Damm.
»*L'interm6diaire des math., 18, 1911, 222; 19, 1912, 87-90; 23, 1916, 14 (generalizations).
^Ihid., 19, 1912, 145, 212, 285. "L'enseignement math., 15, 1913, 217-224

406 History of the Theory of Numbers. [Chap, xvii

R. Niewiadomski^^ noted that, for a series of Pisano,
Uff^a=Ula-hi or -Uia-1 (rnodN),

according as the prime A^ = 10m±lorlOw±3. He showed how to compute
rapidly distant terms of the series of Pisano and similar series, and factored
numerous terms.

L. Bastien^^ employed a prime p and integer a^Kp and determined
02,03, . . .,each <p,bymeansof 0102= Q, 02+ 03—-^, 0304— Q,a4+a5=-P, • . .
(mod p). Then

a2.H-i^f^±^^^^-^'' (modp), K,+, = PK,-QK,_,.

The types of series are found and enumerated. Every divisor of Kp is of
the form Xp±l. Some of Lucas' results are given.

R. D. CarmichaeP^ generalized many of Lucas'^^'^^ theorems and
corrected several. The following is a generalization (p. 46) of Fermat's
theorem: If a-\-^ and aj3 are integers and aj3 is prime to n = pC\ . .pk'',
where p\, . . .,Pk are distinct primes, Uy, = {a^—0^)/{a—^) is divisible by n
when X is the 1. c. m. of

(3) p;rMPi-(a,/3)pj {i=i,...,k).

Here, if p is an odd prime, the symbol (a, ^)p denotes 0, +1 or — 1, according
as {a—^Y is divisible by p, is a quadratic residue of p, or is a quadratic non-
residue of p; while (a, /3)2 denotes +1 if a/3 is even, 0 if a^ is odd and a-\-^ is
even, and —1 if aj8(a+j3) is odd. In particular, if </> is the product of the
numbers (3), •w^=0(mod n), which is the corrected form of the theorem of
Lucas'".

Relations have been noted®° between terms of recurring series defined by
one of the equations

^n + W„ + l='W„+2, 'W„ + Wn+2 = W„+3, y„+i + t'„_i = 4y„, ^1=1,^2 = 3.

E. Malo^^ and Prompt^ ^ considered the residues with respect to a prime
modulus 10m='=l of the series Uq, Ui, U2 = Uo-\-Ui,. . ., ii„ = w„_i+w„_2.

A. Boutin^^ noted relations between terms of Pisano's series.

A. Agronomof^^ treated it„ = it„_i+it„_2+w„_3.

Boutin^^ and Malo^^ treated sums of terms of Pisano's series.

A. Pellet^'' generalized Lucas' ^^ law of apparition of primes.

A. G^rardin^^ proved theorems on the divisors of terms of Pisano's
series.

»'L'interm6diaire des math., 20, 1913, 51, 53-6.

"Sphinx-Oedipe, 7, 1912, 33-38, 145-155.

"Annals of Math., (2), 15, 1913, 30-70.

•"Math. Quest. Educat. Times, 23, 1913, 55; 25, 1914, 89-91.

"L'intermddiaire des math., 21, 1914, 86-8.

"Ibid., 22, 1915, 31-6. "Mathesis, (4), 4, 1914, 125.

"Mathesis, (4), 4, 1914, 126. "L'interm^diaire des math., 23, 1916, 42-3.

••L'intermediaire des math., 23, 1916, 64-7 "Nouv. Ann. Math., (4), 16, 1916, 361-7.

Chap. XVII] ALGEBRAIC THEORY OF RECURRING SERIES. 407

E. Piccioli^^ noted that in Pisano's series 1, 1, 2, 3, . . .,

according as A; is odd or even.

T. A. Pierce®^ proved for the two functions HlZiil^aD of the roots ai
of an equation with integral coefficients properties analogous to those of
Lucas' Un, Vn.

Algebraic Theory of Recurring Series.

J. D. Cassini^°° and A. de Moivre^"^ treated series whose general term is
a sum of a given number of preceding terms each multiplied by a constant.
D. Bernoulli^°^ used such recurring series to solve algebraic equations. J.
Stirling^°^ permitted variable multipUers.

L. Euler^°^ studied ordinary recurring series and their application to
solving equations.

J. L. Lagrange^°^ made the subject depend on the integration of linear
equations in finite differences, treating also recurring series with an additive
term. The general term of such a series was found by V. Riccati.^°®

P. S. Laplace^"^ made systematic use of generating functions and applied
recurring series to questions on probability.

J. L. Lagrange^°^ noted that if Ay^-\-Byi.^i-}- . . .-\-Nyt+n = 0 is the
recurring relation and if A+Bt-{- . . .+iVT = 0 has distinct roots a, jS, . . .,
the general term of the series is y^ = aa^+&/3'^+ • ■ • • For the case of multiple
roots he stated a formula which G. F. Malfatti^°^ proved to be erroneous;
the latter gave a new process explained for 2, 3 or 4 equal roots.

Lagrange^^° had noticed independently his error and now gave the
general term of a recurring series in the case of multiple roots by a more
direct process than that of Malfatti.

Pietro Paoli^^^ investigated the sum of a recurring series.

98Periodico di Mat., 31, 1916, 284-7.
s'Annals of Math., (2), 18, 1916, 53-64.
""Histoire acad. roy. sc. Paris, annee 1680, 309.
"iPhil. Trans. London, 32, 1722, 176; Miscellanea analytica, 1730, 27, 107-8; Doctrine of

chances, ed. 2, 1738, 220-9.
i»2Comm. Acad. Petrop., 3, ad annum 1728, 85-100.
lO'Methodus differentialis, London, 1730, 1764.
"^Introductio in analysin infinitorum, 1748, I, Chs. 4, 13, 17. Cf . C. F. Degen, Det K. Danske

Vidensk. Selskabs Afhand., 1, 1824, 135; Oversigt. . .Forhand., 1818-9, 4.
ii^Miscellanea Taurinensia, 1, 1759, Math., 33-42; Oeuvres, I, 23-36.
"^Mem. present^s div. sav. Paris, 5, 1768, 153-174; Comm. Bonon., 5, 1767. Cf. M. Cantor,

Geschichte Math., lY, 1908, 261.
"^Mem. sav. etr. ac. sc. Paris, 6, annee 1771, 1774, p. 353; 7, annee 1773, 1776; Oeuvres, VIII,

5-24, 69-197. M6m. ac. roy. sc. Paris, ann^e, 1779, 1782, 207; Oeuvres, X, 1-89 (ann^e

1777, 99).
"«Nouv. Mem. Ac. Berlin, annle 1775, 1777, 183-272; Oeuvres, IV, 151.
losMem. mat. fis. soc. Ital., 3, 1786-7, 571.

""Nouv. M6m. Ac. Sc. Berlin, ann^es 1792-3, 247; Oeuvres, V, 625-641 (p. 639 on the error).
">Mem. Acad. Mantova, 1, 1795, 121. See Partitions in Vol. Ill of this History.

408 History of the Theory of Numbers. [Chap, xvii

J. B. Fourier's"^" error in appl^dng recurring series to the solution of
numerical equations was pointed out by R. Murphy.^^^''

P. Frisiani"^" applied recurring series to the solution of equations.

E. Betti^^^'^ emploj'ed doubly recurring series to solve equations in two
unknowns, by extending the method of Bernoulli. ^°'

W. Scheibner^^- considered a series with a three-term recursion formula,
deduced the linear relation between any three terms, not necessarily con-
secutive, and applied his results to continued fractions and Gauss' h>TDer-
geometric series.

D. Andr^^^^ deduced the generating equation of a recurring series F»
from that of a recurring series L'„ given a Unear homogeneous relation
between the terms F, multiplied by constants and the terms C/„, C/„_i, . . .,
multipUed by polynomials in n.

D. Andr^^^^ considered a series Ui, U2, . . ., with

where w„, X„ are given functions of n, X„ being an integer ^n — 1, while
Ai"^ is a given function of k, n. It is proved that

C/„ = 2 ^(n, p)u„ ^(n, p) =i:AiyA[y ....,

p=i

where the second summation extends over all sets of integral solutions of

k\-\-k2+ ■ ■ ■=n-p, ni = ki+p, n< = A\+n<_i (0</:<<Xn,).

Application is made to eight special types of series.

D. Andr^"^ discussed the sums of the series whose general terms are

n(/i+l) . . . {n+p - 1)' {an+j3) !

where w„ is the general term of any recurring series.

G. de Longchamps"^" proved the first result by Lagrange^^^ and
expressed y^ as a sj-mmetric function of the distinct roots a, /3, . . . . He"^*
reduced Un = AiU„_i+ . . +A^L''„_„+/(n), where / is a polj^nomial of de-
gree p, to the case f(n) = 0 by making a substitution ?7„= F„-f-Xon^+ . . -\-\p.

C. A. Laisant^^^*" studied the ratios of consecutive terms of recurring
series, in particular for Pisano's series.

'""Analyse des Equations, Paris, 1831.

'»»Phil. Mag., (3), 11, 1837, 38-40.

"'•^Effemeridi .\stronomiche di Milano, 1850, 3.

"I'^Annali di Sc. Mat. Fis., 8, 1857, 48-61.

"«Berichte Gesell. Wiss. Leipzig (Math.), 16, 1864, 44-68.

i"Bull. Soc. Math. France, 6, 1877-8, 166-170.

"«Aim. 8C. r^cole norm, sup., (2), 7, 1878, 375-408; 9, 1880, 209-226. Summary in Bull, dea

Sc. Math., (2), 1, I, 1877, 350-5.
"HIbmptes Rendus Paris, 86, 1878, 1017-9; 87, 1878, 973-5.
'"^Assoc. frang., 9, 1880, 91-6.
"»*7&id., 1885, II, 94-100.
»"«Bull. dea Sc. Math., (2), 5, I, 1881, 218-249.

Chap. XVII] AlGEBEAIC ThEORY OF RECURRING SeRIES. 409

M. d'Ocagne^^^ considered the recurring series Ui with

and with Uq, . . ., Up_i arbitrary; and the series u with the same law, but
with Ui = 0 {i = 0,. . ., p — 2), Up_i = l. Then

Un=UoUn+p-i-\-{Ui-aiUo)Un+p-2+ ■ ■ • + ( C/p_i " ^i f7p_2 - . . . -ap_iC/o)^n-

For each series he found the sum of any fixed number of consecutive terms
and the Hmit of that sum.

M. d'Ocagne^^^ treated Up+^ = Up^n-i+ ■ ■ ■ +Un' He^^^ discussed the con-
vergents to a periodic continued fraction by use of t«„ = atW„_i + ( — l)*w„_2,

L. Gegenbauer^^^" found the solution Pm of gnPn = 2^UnPn—i+i/nPn-2,
where

S. Pincherle^^^^ applied p„+i(x) = (a; — aj(x— i8„)p„(a;) to developments in
series.

E. Study "^^ showed how to express the general term of a recurring series
as a sum of the general terms of simpler recurring series, exhibited explicitly
the general term when n = 3, and applied the theory to bilinear forms.

M. d'Ocagne^^^ considered a recurring series with the law of recurrence

(^1, . . . , Ap) : F„+AiF„_i+ . . . -{-ApYn—p^O

of order p and generating equation

^{x)=x''+Aix''-'+ . . . +Ap-=0.
Set
Qi{x)=x'+A,x'-'+ . . . +A„ ^{x) = Yp_,+Q,{x)Yp-2+ ■ ■ • +Qp-iix)Yo.

The existence of a conomon root a of $(x) =0, '^ (a;) =0 is a necessary and
sufficient condition that the Y's satisfy also a law of recurrence of order
p — 1, viz., (Qi(a),. . ., Qp_i(a)), and then the initial law of recurrence is
said to be reducible to one of order p — 1.

M. d'Ocagne^^'' considered the series with the law of recurrence

U^n — ^*0 '^ n—l + a itt n—2 "T • • • + Ct Pi—lU n—Pi

and generating equation

(l>iix) =x^' — a\ of *~^ — ... — a*p.._i,

"«Nouv. Ann. Math., (3), 2, 1883, 220-6; 3, 1884, 65-90; 9, 1890, 93-7; 11, 1892, 526-532 (5,
1886, 257-272). BuU. Soc. Math. France, 12, 1883-4, 78-90 (case p = 2); 15, 1886-7,
143-4; 19, 1890-1, 37-9 (minor applications). Nieuw Archief voor Wiskunde, 17, 1890,
229-232 (applications to sin ma as function of sin a and cos a).

"'Comptes Rendus Paris, 104, 1887, 419-420; errata, 534.

"8/bid., 108, 1889, 499-501.

"s^Sitzungsber Ak. Wiss. Wien (Math.), 97, Ila, 1888, 82-89.

"s^Atti R. Accad. Lincei, Rendiconti, 5, 1889, I, 8-12, 323-7.

"8cMonatshefte Math. Phys., 2, 1891, 22-54.

"'Bull. Soc. Math. France, 20, 1892, 121-2.

"oComptes Rendus Paris, 115, 1892, 790-2; errata, 904.

410

History of the Theory of Numbers.

[Chap. XVII

such that, for I = 0, Uq= . . . = Wp_2 = 0, Up_i = 1 . If 4>o{x) = </)i(x)- • • </>„(x) ,

U n+p-l =2W r^+p^-l' ' "^"""w+P^-l'

summed for all combinations of n's for which tzj + . . . -\-n^ = n. Application
is made to the sum of a recurring series with a variable law of recurrence.

M. d'Ocagne^-^ reproduced the last result, and gave a connected expo-
sition of his earlier results and new ones.

R. Perrin^" considered a recurring series U of order p ^ith the terms
Uq,Ui,. . .. The general term of the A-th derived series of U is defined to be

u

(*)_

Un+1
Wn+2

Un+k

• • 'Un+2k

ies is zero, the law of recurrence of

If any term of the (p — l)th derived ser
the given series U is reducible (to one of lower order) . If also any term of
the (p — 2)th derived series is zero, continue until we get a non- vanishing
determinant; then its order is the minimum order of U. This criterion is
only a more convenient form of that of d'Ocagne.^^^'^^^

E. ]Maillet^"-^ noted that a necessarj^ condition that a law of recurrence
of order p be reducible to one of order p—q is that ^(x) and ^{x) of
d'Ocagne^^^ have q roots in common, the condition being also sufficient if
$(x)=0 has only distinct roots. He found independently a criterion anal-
ogous to that of Perrin^-- and studied series with two laws of recurrence.

J. Neuberg^^ considered w„ = aw„_i+6u„_2 and found the general term
of the series of Pisano.

C. A. Laisant^^^ treated the case F a constant of d'Ocagne's^^^
u,{f{u)]=Fik).

S. Lattes^^^ treated Wn+p=/(Wn+p-i>- • •> ^J» where / is an analytic
function.

M. .Amsler^^^ discussed recurring series by partial fractions.

E. Netto,^-"'' L. E. Dickson,^-"' A. Ranum,^-^ and T. Hayashi'-^ gave
the general term of a recurring series. N. Traverso^^" gave the general
term for Q„= (n — l)(Q„_i+Q„_2) and u„= aUn-i+hu^_2.

Traverso^^^ applied the theory of combinations with repetitions to express,
as a function of p, the solution of Q„, = p(Qm-i+Qm-2+ • • • +Qm-n)-

'"Jour, de l'6cole polyt., 64, 1894, 151-224.

i=»Comptes Rendus Paris, 119, 1894, 990-3.

i»M6m. Acad. Sc. Toulouse, (9), 7, 1895, 179-180, 182-190; Assoc, fran?., 1895, III, 233 [report

with miscellaneous Dioph. equations of order n, Vol. II); Nouv. Ann. Math., (3), 14,

1895, 152-7, 197-206.
"*Mathesis, (2), 6, 1896, 88-92; Archive de mat., 1, 1896, 230.

"*Bull. Soc. Math. France, 29, 1901, 145-9

""Nouv. Ann. Math., (4), 10, 1910, 90-5.

^"'-Amer. Math. Monthly, 10, 1903, 223-6.

"'Bull. Amef. Math. Soc, 17, 1911, 457-461.

"•/Wd., 18, 1912, 191-2.

"oPeriodico di Mat., 29, 1913-4, 101-4; 145-160.

"'Ibid., 31, 1915-6, 1-23, 49-70, 97-120, 145-163, 193-207

i»>Comptes Rendus Paris, 150, 1910, 1106-9.
"'"Monatshefte Math. Phys., 6, 1895, 285-290.

Chap. XVII] ALGEBRAIC THEORY OF RECURRING SERIES. 411

F. Nicita^^^ found many relations like 2aJ^ — hn^= — { — !)'' between
the two series ai = l, 02 = 2,.., an = 2(an+i — «n-i), • • • ; &i = l, 62 = 3,...,

&n = l(^n+l~-^n-l)j • • ••

Reference may be made to the text by A. Vogt^^^ and to texts and papers
on difference equations cited in Encyklopadie der Math. Wiss., I, 2, pp. 918,
935; Encyclopedie des Sc. Math., I, 4, 47-85.

A. Weiss^^^ expressed the general term 4 of a recurring series of order
T linearly in terms of tq, tg_i , . . . , ^q-r+i, where q is an integer.

W. A. Whitworth^^^ proved that, if Co+CiX+C2X^+ ... is a convergent
recurring series of order r whose first 2r terms are given, its scale of relation
and sum to infinity are the quotients of certain determinants.

H. F. Scherk^^^ Started with any triangle ABC and on its sides con-
structed outwards squares BCED, ACFG, ABJH. Join the end points to
form the hexagon DEFGHJ. Then construct squares on the three joining
lines EF, GH, JD and again join the end points to form a new hexagon, etc.
If tti, hi, Ci are the lengths of the joining lines in the iih. set, a„+i = 5a„_i — a„_3.
The nth term is found as usual.

Sylvester^" solved Uj,= u^_i-\-{x — \){x — 2)Ux_2' A._ Tarn^^^ treated
recurring series connected with the approximations to \^2, Vs, Vs.

V. SchlegeP^^ called the development of {1 — x—x^— . . . —x'')~'^ the
(n — l)th series of Lame; each coefficient is the sum of the n preceding.
For n=2, the series is that of Pisano.

References on the connection between Pisano's series and leaf arrange-
ment and golden section (Kepler, Braun, etc.) have been collected by R. C.
Archibald."^

Papers by C. F. Degen,^^^ A. F. Svanberg,^^^ and J. A. Vesz"^ were not
available for report.

"2Periodico di Mat., 32, 1917, 200-210, 226-36.

^'^Theorie der Zahlenreihen u. der Reihengleichung, Leipzig, 1911, 133 pp.

"4Jour. fur Math., 38, 1849, 148-157.

"^Oxford, Cambridge and Dublin Mess. Math., 3, 1866, 117-121; Math. Quest. Educ. Times,

3, 1865, 100-1.
i36Abh. Naturw. Vereine zu Bremen, 1, 1868, 225-236.
• i"Math. Quest. Educ. Times, 13, 1870, 50.
•38Math. Quest, and Solutions, 1, 1916, 8-12.
139E1 Progreso Mat., 4, 1894, 171-4.
""Amer. Math. Monthly, 25, 1918, 232-8.
i"M6m. Acad. Sc. St. Petersbourg, 1821-2, 71.
i«2Nova Acta R. Soc. Sc. UpsaUensis, 11, 1839, 1.
i«EIrtekez. a Math., Magyar Tudom. Ak. (Math. Memoirs Hungarian Ac. Sc), 3, 1875, No. 1.

CHAPTER XVIII.

THEORY OF PRIME NUMBERS.
Existence of an Infinitude of Primes.

Euclid^ noted that, if p were the greatest prime, and M = 2-S-5. . .p is
the product of all the primes ^p, then M+l is not divisible by one of
those primes and hence has a prime factor >p, thus involving a contra-
diction.

L. Euler^ deduced the theorem from the [invahd] equation

s -=n(i--) ,

„=in V p/

the left member being infinite and the right finite if there be only a finite
number of primes. Euler^ concluded from the same equation that "the
number of primes exceeds the number of squares."

Euler^ modified Euclid's^ argument slightly. The number of integers
<M and prime to M is <t>(M) =2-4. . . (p — 1), so that they include integers
which are either primes >p or have prime factors >p.

The theorem follows from Tchebychef's^^^ proof of Bertrand's postulate.

L. Kronecker^ noted that we may rectify Euler's^ proof by using

2 -^=nfl-i) ' (s>l).

where p ranges over all primes > 1 . If there were only a finite number of
p's, the product would remain finite when s approaches unity, while the
sum increases indefinitely. He also gave the proof a form leading to an
interval from m to n within which there exists a new prime however great
m is taken.

R. Jaensch® repeated Euler's- argument, also ignoring convergency.

E. Kummer'^ gave essentially Euler's'* argument.

J. Perott^ noted that, if pi,. . ., p„ are the primes ^N, there are 2"
integers ^N which are not divisible by a square, and

2">iV-

"-mx'-^i^'^'-iyi-

Hence there exist infinitely many primes.

L. Gegenbauer^" proved the theorem by means of 2"ii*n~*.

lElementa, IX, 20; Opera (ed., Heiberg), 2, 1884, 388-91.

^Introductio in analysin infinitorum, 1, Ch. 15, Lausanne, 1748, p. 235; French transl. by

J. B. Labey, 1, 218.
'Comm. Acad. Petrop., 9, 1737, 172-4.

^Posthumous paper. Coram. Arith. Coll., 2, 518, Nos. 134-6; Opera Postuma, I, 1862, 18.
'Vorlesungen uber Zahlentheorie, I, 1901, 269-273, Lectures of 1875-6.
*Die Schwierigeren Probl. Zahlentheorie, Progr. Rastenburg, 1876, 2.
'Monatsber. Ak. Wiss. Berlin fiir 1878, 1879, 777-8.
sBull. sc. math, et astr., (2), 5, 1881, I, 183-4.
8«Sitzungsber. Ak. Wiss. Wien (Math.), 95, II, 1887, 94-6; 97, Ila, 1888, 374-7.

413

414 History of the Theory of Numbers. [Chap, xviii

J. Perott' applied the theory of commutative groups to show that,
if Q\,- ■ ■) Qn are primes, there exist at least n — 1 primes between g„ and
M = qi- ■ Qn'

T. J. Stieltjes^° expressed the product P of the primes 2, 3, . . ., p as a
product AB of two factors in any way. Since A-{-B is not divisible by
2, . . . , p, there exists a prime >p.

J. Hacks" proved the existence of an infinitude of primes by use of his
formula (Ch. XI, Hacks^^) for the number of integers ^m not divisible
by a square.

C. 0. Boije af Gennas^^ showed how to find a prime exceeding the nth
primep„>2. Take P = 2'''3'''. . Pn*^, each ^^,^1. Express P as a product
of relatively prime factors 5, P/8, where Q = P/8—8>l. Since Q is divisible
by no prime ^ p„, it is a product of powers of primes qi'^pn+2. Take 5 so
that Q< (p„+2)l Then Q is a prime.

Axel Thue^^ proved that, if (l+n)*<2", there exist at least k-{-l
primes <2''.

J. Braun^'" noted that the sum of the inverses of the primes ^p is, for
p^ 5, an irreducible fraction > 1 ; hence the numerator contains at least one
prime >p. He attributed to Hacks a proof by means of 11(1 — l/p-)~^ =
2s~^ = TT^/G ; the product would be rational if there were only a finite number
of primes, whereas tt is irrational.

E. Cahen^^ proved the ''identity of Euler" used by Kjonecker.^

Stormer-^^ gave a proof.

A. Le\'y^^ took a product P of k of the first n primes Pi,. . ., p„ and
the product Q of the remaining n — k. Then P+Q is either prime or has
a prime factor >p„; like\\'ise for P — Q. If p„ is a prime such that p„+2 is
composite, there exist at least n primes >p„, but ^l+PiP2- • Pn- When

1 1

± ± db

Pi '" Pn

is reduced to a simple fraction, the numerator has no factor in common with
Pi . . .p„; hence there is a prime >Pn- He considered (pp. 242-4) the primes
defiiied by a;(x — 1) — 1 for consecutive integers x.

A. Auric^^ assumed that pi, . . . , pk give all the primes. Then the number
of integers < 71 =npi°' is

which is small in comparison with n, whence k increases indefinitely with n.

»Amer. Jour. Math., 11, 1888, 9&-138; 13, 1891, 235-308, especially 303-5.
"Annales fac. sc. de Toulouse, 4, 1890, 14, final paper.
"Acta Math., 14, 1890-1, 335.

'Hifversigt K. Sv. Vetenskaps-Akad. Forhand., Stockholm, .50, 1893, 469-471.
"Archiv for Math, og Xatur., Kristiania, 19, 1897, No. 4, 1-5.
'*^Das Fortschreitungsgesetz der Primzahlen durch eine transcendente Gleichung exakt

dargestellt, WLss. Beilage Jahresbericht, Gymn., Trier, 1899, 96 pp.
"filaments de la th^orie des nombres, 1900, 319-322.
"Bull, de Math. £l6mentaires, 15, 1909-10, 33-34, 80-82.
"L'interm^diaire des math., 22, 1915, 252.

I

Chap. XVIII] INFINITUDE OF PrIMES. 415

G. M^trod^'^ noted that the sum of the products n — 1 at a time of the
first n prunes > 1 is either a prime or is divisible by a prime greater than the
nth. He also repeated Euler's^ proof.

Infinitude of Primes in a General Arithmetical Progression.

L. Euler^'' stated that an arithmetical progression with the first term
unity contains an infinitude of primes.

A. M. Legendre^^ claimed a proof that there is an infinitude of primes
2mx+ii if 2m and /x are relatively prime.

Legendre^^ noted that the theorem would follow from the following
lemma: Given any two relatively prime integers A, C, and any set of k odd
primes d,\,. . ., co [not divisors of A], and denoting the zth. odd prime by
7r^^\ then among tt'*"^' consecutive terms of the progression A — C, 2A — C,
3A — C,. . . there occurs at least one divisible by no one of the primes
6,. . ., CO. Although Legendre supposed he had proved this lemma, it is
false [Dupr^28j^

G. L. Dirichlet^^ gave the first proof that mz-\-n represents infinitely
many primes if m and n are relatively prime. The difficult point in the
proof is the fact that

n=i n

where x(^) =0 if ^j ^ have a common factor > 1, while, in the contrary case,
xin) is a real character different from the chief character of the group of
the classes of residues prime to k modulo k. This point Dirichlet proved
by use of the classes of binary quadratic forms.

Dirichlet^'* extended the theorem to complex integers.

E. Heine^^ proved "without higher calculus" Dirichlet's result

VJ? p[jHW^''^{b+2ay+'>~^ ■■■}'= a

A. Desboves^^ discussed the error in Legendre's^^ proof.
L. Durand^^ gave a false proof.

A. Dupre^^ showed that the lemma of Legendre^" is false and gave
(p. 61) the following theorem to replace it: The mean number of terms,

"L'intermediaire des math., 24, 1917, 39-40.

^oOpusc. analytica, 2, 1785 (1775), 241; Comm. Arith., 2, 116-126.

2iMem. ac. sc. Paris, ann^e 1785, 1788, 552.

22Theorie des nombres, ed. 2, 1808, p. 404; ed. 3, 1830, II, p. 76; Maser, 2, p. 77.

23Bericht Ak. Wiss. Berlin, 1837, 108-110; Abhand. Ak. Wiss. Berlin, Jahrgang 1837, 1839,

Math., 45-71; Werke, 1, 1889, 307-12, 313-42. French transl., Jour, de Math., 4, 1839,

393-422. Jour, fiir Math., 19, 1839, 368-9; Werke, 1, 460-1. Zahlentheorie, §132, 1863;

ed. 2, 1871; 3, 1879; 4, 1894 (p. 625, for a simplification by Dedekind).
z^Abhand. Ak. Wiss. BerUn, Jahrgang 1841, 1843, Math., 141-161; Werke, 1, 509-532. French

transl., Jour, de Math., 9, 1844, 245-269.
2«Jour. fiir Math., 31, 1846, 133-5.
26Nouv. Ann. Math., 14, 1855, 281.
^Ubid., 1856, 296.
^^Examen d'une proposition de Legendre, Paris, 1859. Comptes Rendus Paris, 48, 1859, 487.

416 History of the Theory of Numbers. iChap. xviii

prime to ^,X,. . ., co, contained in tt**"^^ consecutive terms of the progression
is ^p-'Q7r"'-''-2, where P = 3-5-7-ll . . ., (?= (3-l)(5-l) . . ..

J. J. Sylvester-^ gave a proof.

V. I. Berton^^" found h such that between x and xh occur at least 2g
primes each of one of the 2g linear forms 2py+ri, where ri, . . ., r2g are the
integers < 2p and prime to 2p.

C. ]Moreau^° noted the error in Legendre's-- proof.

L. Kronecker^ (pp. 442-92) gave in lectures, 1886-7, the following
extension* of Dirichlet's theorem (in lectures, 1875-6, for the case m a
prime): If jjl is any given integer, we can find a greater integer v such that,
if 7u, r are any two relatively prime integers, there exists at least one prime
of the form h7?i+r in the interval from /x to ^' (p. 11, pp. 465-6). Moreover
(pp. 478-9), there is the same mean density of primes in each of the <l){m)
progressions mh-\-ri, where the r, are the integers <?n and prime to m.

I. Zignago^^ gave an elementary proof.

H. Scheffler^^ devoted 31 pages to a re\nsion of Legendre's insufficient
proof and gave a process to determine all primes under a given limit.

G. Speckmann^^ failed in an attempt to prove the theorem.

P. Bachmann^^ gave an exposition of Dirichlet's^^ proof.

Ch. de la Vallee-Poussin^^ obtained without computations, by use of
the theorj' of functions of a complex variable, a proof of the difficult point
in Dirichlet's^^ proof. He^® proved that the sum of the logarithms of the
primes hk-\-l^x equals x/4>{k) asymptotically and concluded readily that
the number of primes hk+l'^x equals, asjonptotically,

4> {x) log X

F. Mertens^^ proved the existence of an infinitude of primes in an arith-
metical progression by elementarj^ methods not using the quadratic reci-
procity theorem or the number of classes of primitive binary quadratic forms.
He supplemented the theorem by showing how to find a constant c such
that between x and ex there lies at least one prime of the progression for
every x^l [cf. Kronecker,^ pp. 480-96].

"Proc. London Math. Soc, 4, 1871, 7; Messenger Math., (2), 1, 1872, 143-4; Coll. Math. Papers,

2, 1908, 712-3.
""Comptes Rendus Paris, 74, 1872, 1390.

">Nouv. Ann. Math., (2), 12, 1873, 323-4. Also, A. Piltz, Diss., Jena, 1884.
•Improvements in the exposition were made by the editor, Hensel (cf. p. 508).
«Annan di Mat., (2), 21, 1893, 47-55.

**Beleuchtung u. Beweis eines Satzes aus Legendre's Zahlentheorie [H, 1830, 76], Leipzig, 1893.
"Archiv Math. Phys., (2), 12, 1894, 439-441. Cf. (2), 15, 1897, 326-8.
"Die analytische Zahlentheorie, 1894, 51, 74-88.
**M6ra. couronnes. . .acad. roy. sc. Belgique, 53, 1895-6, No. 6, 24-9.
*Annales de la soc. sc. de Bru.xeUes, 20, 1896, II, 281-361. Cf. 183-256, 361-397; 21, 1897, I,

1-13, 60-72; II, 251-368.
"Sitzungsber. Ak. Wiss. Wien (Math.), 106, 1897, II a, 254-286. Parts published earlier,

ibid., 104, 1895, II a, 1093-1121, 1158-1166; Jour, fiir Math., 78, 1874, 46-62; 117, 1897,

169-184.

Chap. XVIII] INFINITUDE OF PRIMES. 417

F. Mertens^^ gave a proof, still simpler than his" earlier one, of the
difficult point in Dirichlet's-^ proof. The proof is very elementary, involv-
ing computations of finite sums.

F. Mertens^^ gave a simplification of Dirichlet's^ proof of his general-
ization to complex primes.

H. Teege^° proved the difficult point in Dirichlet's^^ proof.

E. Landau'*^ proved that the number of prime ideals of norm ^ a: of an
algebraic field equals the integral-logarithm Li(x) asymptotically. By
specialization to the fields defined by V — 1 or V — 3? we derive theorems'*^
on the number of primes 4:k^l or 6A;=fcl ^x.

L. E. Dickson^^ asked if aifi+bi {i = l,. . ., m) represent an infinitude of
sets of m primes, noting necessary conditions.

H. Weber^^ proved Dirichlet's^^ theorem on complex primes.

E. Landau^^ simplified the proofs by de la Vallee-Poussin^^ and Mertens.^*

E. Landau*^'^^ simplified Dirichlet's^^ proof. Landau^^ proved that,
if k, I are relatively prime, the number of primes ky-\-l^x is

where 7 is a constant depending on k. For 0 see Pfeiffer^° of Ch. X.

A. Cunningham*^ noted that, of the N primes ^R, approximately
N/c{)(n) occur in the progressions nx-\-a, a<n and prime to n, and gave a
table showing the degree of approximation when R = 10^ or 5-10^, with
n even and < 1928. Within these limits there are fewer primes nx-\-l than
primes nx+a, a>l.

Infinitude of Primes Represented by a Quadratic Form.

G. L. Dirichlet^^ gave in sketch a proof that every properly primitive
quadratic form {a, h, c), a, 26, c with no common factor, represents an infini-
tude of primes.

Dirichlet^^ announced the extension that among the primes represented
by {a, b, c), an infinitude are representable by any given linear form Mx-\-N,
with M, N relatively prime, provided a, h, c, M, N are such that the linear
and quadratic forms can represent the same number.

»8Sitzungsber. Ak. Wiss. Wien (Math.), 108, 1899, II a, 32-37.

"/bid., 517-556. Polish transl. in Prace mat. fiz., 11, 1900, 194-222.

"Mitt. Math. GeseU. Hamburg, 4, 1901, 1-11.

*iMath. Amialen, 56, 1903, 665-670.

*?Sitzungsber. Ak. Wiss. Wien (Math.), 112, 1903, II a, 502-6.

"Messenger Math., 33, 1904, 155.

"Jour, fur Math., 129, 1905, 35-62. Cf. p. 48.

«Sitzungsber. Akad. Berlin, 1906, 314-320.

«Rend. Circ. Mat. Palermo, 26, 1908, 297.

"Handbuch . . .Verteilung der Primzahlen, I, 1909, 422-35.

"Sitzungsber. Ak. Wiss. Wien (Math.), 117, 1908, Ila, 1095-1107.

"Proc. London Math. Soc, (2), 10, 1911, 249-253.

"Bericht Ak. Wiss. Berhn, 1840, 49-52; Werke, 1, 497-502. Extract in Jour, fiir Math., 21,

1840, 98-100.
"^Comptes Rendus Paris, 10, 1840, 285-8; Jour, de Math., 5, 1840, 72-4; Werke, 1, 619-623.

418 History of the Theory of Numbers. [Chap, xviii

H. Weber^^ and E. Schering^^ completed Dirichlet's^^ proof of his first
theorem. A. Meyer^^ completed Dirichlet's^^ proof of his extended theorem.

F. Mertens^" gave an elementary proof of Dirichlet's^^ extended theorem.

Ch. de la Vall^e-Poussin^^ proved that the number of primes ^ x repre-
sentable by a properly primitive definite positive or indefinite^^ irreducible
binary' quadratic form is asjTnptotic to gx/\ogx, where ^ is a constant; and
the same for primes belonging also to a linear form compatible with the
character of the quadratic form.

L. Kronecker^ (pp. 494-5) stated a theorem on factorable forms in
several variables which represent an infinitude of primes.

Elementary Proofs of the Existence of an Infinitude of Primes mz+l,

FOR Any Given m.

V. A. Lebesgue^^ gave a proof for the case m a prime, using the fact
that x^~^ — x"'~~y+ . . . +y"'~^ has besides the possible factor m only prime
factors 2km + 1. A like method apphes^^ to 2mz — l.

J. A. Serret^^ gave an incomplete proof for any m.

F. Landry^^ gave a proof like Lebesgue's.®^ If ^ is the largest prime
2km-\-l and if x is the product of all of them, a:'"+l is divisible by no one
of them. Since (x'"+l)/(x+l) has no prime divisor not of the form
2km+l, there exists at least one >d.

A. Genocchi^^ proved the existence of an infinitude of primes mz^ 1
and n'2±l for n a prime by use of the rational and irrational parts of

(a+Vb)'-

L. Kronecker^ (pp. 440-2) gave in lectures, 1875-6, a proof for the case
m a prime; the simple extension in the text to any m was added by Hensel.

E. Lucas gave a proof by use of his w„ (Lucas,^^ p. 291, of Ch. XYII).

A. Lefebure^° of Ch. XVI stated that the theorem follows from his
results.

L. Kraus^^ gave a proof.

A. S. Bang"'' and Sylvester^ proved it by use of cyclotomic functions.

K. Zsigmondy"^ of Ch. VII gave a proof. Also, E. Wendt,'^ and
Birkhoff and Vandiver^^ ^f q^ ^VI.

»^Math. Annalen, 20, 1882, 301-329. Elliptische Functionen (= Algebra, III), ed. 2, 1908,

613-6.
»8Werke, 2, 1909, 357-365, 431-2.

"Jour, fur Math., 103, 1888, 98-117. Exposition by Bachmaim,»< pp. 272-307.
•oSitzungsber. Ak. Wiss. Wien (Math.), 104, 1895, Ila, 1093-1153, 1158. Simplification,

ibid., 109, 1900, Ila, 415-480.
"Cf. E. Landau, Jahresber. D. Math. Verein., 24, 1915, 250-278.
"Jour, de Math., 8, 1843, 51, note. Exercices d'analyse num^rique, 1859, 91.
«''.Jour. de Math., (2), 7, 1862, 417.
•«Jour. de Math., 17, 1852, 186-9.

•'Deuxidme mdmoire but la thdorie des nombres, Paris, 1853, 3.
"AnnaU di mat., (2), 2, 1868-9, 256-7. Cf. .Genocchi==- " of Ch. XVII.
••Casopis Math, a Fys., 15, 1886, 61-2. Cf. Fortschritte, 1886, 134-5.
^Tidsskrift for Math., (5), 4, 1886, 70-80, 130-7. See Bang". ", Ch. XVI.
"Jour, fiir Math., 115, 1895, 85.

i

Chap. XVIII] INFINITUDE OF PRIMES. 419

N. V. Bervi^^ proved that the ratio of the number of integers cm+1 not
>n and not a product of two integers of that form to the number of all
primes not >n has the limit unity for n= oo .

H. C. Pocklington^^ proved that, if n is any integer, there is an infinitude
of primes mn+1, an infinitude not of this form if n>2, and an infinitude
not of the forms mn±l if n = 5 or n>6.

E. Cahen^^ proved the theorem for m an odd prime.

J. G. van der Corput'^^ proved the theorem.

Elementary Proofs op the Existence of an Infinitude of Primes in
Special Arithmetical Progressions.

J. A. Serret^^ for the common difference 8 or 12, and for lOx+9.

V. A. Lebesgue»° for 4n±l, Sn+k (/c = l, 3, 5, 7). Lebesgue^^ for the
same and 2'"n+l, Qn — 1. Also, by use of infinite series, for the common
difference 8 or 12.

E. Lucas«2 f<3j. 5n-\-2, 8n+7.

J. J. Sylvester^^ for the difference 8 or 12 and^ for p^x — 1, p a prime.

A. S. Bang^^ for the differences 4, 6, 8, 10, 12, 14, 18, 20, 24, 30, 42, 60.

E. Lucas^^ for 4n=i=l, 6n — 1, Sn+5.

R. D. von Sterneck" for an — 1.

K. Th. Vahlen^^ for mz-\-l by use of Gauss' periods of roots of unity.
Also, if m is any integer and p a prime such that p — 1 is divisible by a higher
power of 2 than <^(m) is, while A; is a root of km + 1^ —1 (mod p), the linear
form mpx+km-^-l represents an infinitude of primes; known special cases
are mx+1 and 2px — l.

J. J. Iwanow^^ for the difference 8 or 12.

E. Cahen^^ (pp. 318-9) for 4a;± 1, 6x± 1, 8a:+5. K. HenseP (pp. 438-9,
508) for the same forms. M. Bauer^° for an — 1.

E. Landau^^ (pp. 436-46) for /cn±l.

I. Schur^^ proved that if f= 1 (mod k) and if one knows a prime '>(f>(k)/2
of the form kz+l, there exists an infinitude of primes kz+l; for example,

2»z-\-2''-^=i=l, Smz-\-2m+l, Smz+4m-\-l, 8m2+6m+l,

where m is any odd number not divisible by a square.

K. Hensep2 f^j. 4^±i^ 6n±l, 8n-l, 8n=t3, 12n-l, lOn-1.

"Mat. Sbornik (Math. Soc. Moscow), 18, 1896, 519.

"Proc. Cambr. Phil. Soc, 16, 1911, 9-10. '^Nouv. Ann. Math., (4), 11, 1911, 70-2.

^^Nieuw Archief voor Wiskunde, (2), 10, 1913, 357-361 (Dutch).

8«Nouv. Ann. Math., 15, 1856, 130, 236.

"Exercices d'analyse num^rique, 1859, 91-5, 103-4, 145-6.

s^Amer. Jour. Math., 1, 1878, 309. saQomptes Rendus Paris, 106, 1888, 1278-81, 1385-6.

s^Assoc. frang. av. sc, 17, 1888, II, 118-120.

s^Nyt Tidsskrift for Math., Kjobenhavn, 1891, 2B, 73-82.

s^Theorie des nombres, 1891, 353-4. "Monatshefte Math. Phys., 7, 1896, 46.

8'Schriften phys.-okon. Gesell. Konigsberg, 38, 1897, 47.

"Math. Soc. St. Petersburg, 1899, 53-8 (Russian).

'"Jour, fur Math., 131, 1906, 265-7; transl. of Math. 6s Phys. Lapok, 14, 1905, 313.

9iSitzungsber. BerUn Math. Gesell., 11, 1912, 40-50, with Archiv M. P.

92Zahlentheorie, 1913, 304-5.

420 History of the Theory of Numbers. [Chap, xvin

R. D. CannichaeP for p*n — 1 (p an odd prime) and 2*-3m — 1.
M. Bauer's^ paper was not available for report.

Polynomials Representing Numerous Primes.

Chr. Goldbach^^" noted that a polynomial fix) cannot represent primes
exclusively, since the constant term would be unit}'-, whereas it is f{p)
in /(x+p).

L. Euler^"^ proved this by noting that, if /(«) =A,f(nA-\-a) is divisible
by A.

Euler^°- noted that x^ — t+41 is a prime for a: = 1, . . . , 40.

Euler^"^ noted that a:- +2:+ 17 is a prime for x = 0, 1, . . ., 15 and [error]
16; x'^+x+41 is a prime for x = 0, 1, . . ., 15.

A. M. Legendre^^ noted that x^+a:+41 is a prime for x = 0, 1,. . ., 39,
that 2x^+29 is a prime for x = 0, 1, . . ., 28, and gave a method of finding
such functions. [Replacing x by x+1 in Euler's^°- function, we get
X-+X+41.] If j8^-|-2(a+i3)x — 13x^ is a square only when x=0, and a and
j3 are relatively prime, then a^+2aj3+14/3- is a prime or double a prime.
He gave many such results.

Chabert^"^" stated that 37i^-f 3n+l represents many primes for n small.

G. 01tramare^°^ noted that x^+ax+6 has no prime divisor ^/z and
hence is a prime when <fjr, if a^—4b is a quadratic non-residue of each of
the primes 2, 3, . . ., ix. The function x^+ax+(a^+163)/4 is suitable to
represent a series of primes. Taking x = 0, a=ii/v, he stated that u^+lQSv^
or its quotient by 4 gives more than 100 primes between 40 and 1763.

H. LeLasseur^"^ verified that, for a prime A between 41 and 54000,
x^+x+A does not represent primes exclusively for x = 0, 1,. . ., A— 2.

E. B. Escott^"" noted that x"+x+41 gives primes not only forx = 0, 1,
. . . , 39, but also^*^^ for x= — 1, — 2, . . . , —40. Hence, replacing x by x— 40,
we get x^ — 79x + 1601, a prime for x = 0, 1, . . ., 79. Several such functions
are given.

Escott^"^ examined values of A much exceeding 54000 in x^+x+A
without finding a suitable A>41. Legendre's^*^ first seven formulas for
primes give composite numbers for a = 2, the eighth for a = 3, etc. Escott
foundthatx^+x^+17isaprimeforx= — 14, — 13, . . ., +10. Inx^— x^ — 17
replace x by x — 10; we get a cubic which is a prime for x = 0, 1, . . . , 24.

"Annals of Math., (2), 15, 1913, 63-5. ^Archiv Math. Phvs., (3), 25, 1916, 131^.

""Corresp. Math. Phys. (ed., Fuss), I, 1843, 595, letter to Euler, Nov. 18, 1752.

'oiNovi Comm. Acad. Petrop., 9, 1762-3, 99; Comm. Arith., 1, 357.

i^M^m. de Berlin, ann^e 1772, 36; Comm. Arith., 1, 584.

"'K)pera postuma, I, 1862, 185. In Pascal's Repertorium Hoheren Math., German transl. by

Schepp, 1900, 1, 518, it is stated incorrectly to be a prime for the first 17 values of x; Uke-

wise by Legendre, Th^orie des nombres, 1798, 10; i808, 11.
iMTh^oric des nombres, 1798, 10, 304-312; ed. 2, 1808, 11, 279-285; ed. 3, 1830, I, 248-255;

German transl. by Maser, I, 322-9. '<»<'Nouv. Ann. Math., 3, 1844, 250.

i^M^m. rinat. Nat. Genevois, 5, 1857, No. 2, 7 pp.

•"Nouv. Corresp. Math., 5, 1879, 371; quoted in rinterm^diaire des math., 5, 1898, 114-5.
'"L'intermddiaire des math., 6, 1899, 10-11.

"•The same 40 primes as for x=0, . . ., 39, as noted by G. Lemaire, ibid., 16, 1909, p. 197.
'"/Wd., 17, 1910, 271.

Chap. XVIII] GoLDBACH's THEOREM. 421

E. Miot^i^ stated that x^- 2999a; +2248541 is a prime for 1460^0;^ 1539.

G. Frobenius"^ proved that the value of x^+xy+py^ is a prime if <p^,
that of 2x^+py^ (y odd) if <p(2p+l), that of x'^+2py^ (x odd) if <p(p-\-2),
and noted cases in which an indefinite form x^-\-xy—qy^ is a prime.

Levy^^ examined x^—x — 1. He"^ considered f{x) = ax^-{-ahx-{-c, where
a, h, c are integers, 0^a<4. Giving to x the values 0, 1, 2, . . ., we get a
set of integers such that, for every n exceeding a certain value, f{n) is
either prime or admits a prime factor which divides a number f(p), where
p<n. For example, if for f{x) =a;^ — a:+41 we grant that /(O), /(I), /(2),
/(3) and /(4) are primes, we can conclude that f{x) is prime for x^^O.
Likewise when 41 is replaced by 11 or 17. Again, 2a;^ — 2a:+19 and 3x^ — 3a;
+23 give successions of 18 and 22 primes respectively. Bouniakowsky^^
of Ch. XI considered polynomials which represent an infinitude of primes.

Braun^^" proved that there exists no quotient of two polynomials such
that the greatest integer contained in its numerical value is a prime for all
integral values > A; of the variable.

Goldbach's Empirical Theorem: Every Even Integer is a Sum of

Two Primes.

Chr. Goldbach^^° conjectured that every number N which is a sum of two
primes is a sum of as many primes including unity as one wishes (up to N),
and that every number >2 is a sum of three primes.

L. Euler^^^ remarked that the first conjecture can be confirmed from an
observation previously communicated to him by Goldbach that every even
number is a sum of two primes. Euler expressed his belief in the last state-
ment, though he could not prove it. From it would follow that, if n is
even, n, n — 2, n — 4:,. . . are the sums of two primes and hence n a sum of
3, 4, 5, . . . primes.

R. Descartes^^^ stated that every even number is a sum of 1, 2 or 3
primes.

E. Waring^^^ stated Goldbach's theorem and added that every odd
number is either a prime or is a suiri of three primes.

L. Euler^^^ stated without profbf that every number of the form 4n+2
is a sum of two primes each of the form 4A;+1, and verified this for 4n+2
^110.

"OL'intermediaire des math., 19, 1912, 36. [From X2+X+41 by setting X=x-1500.]

"iSitz. Ak. Wiss. Berlin, 1912, 966-980.

"^Bull. Soc. Math. France, 1911, Comptes Rendus des Seances. Extract in Sphinx-Oedipe,

9, 1914, 6-7.
i^oCorresp. Math. Phys. (ed., P. H. Fuss), 1, 1843, p. 127 and footnote; letter to Euler, June 7,

1742.
i"/&id., p. 135; letter to Goldbach, June 30, 1742. Cited by G. Enestrom, Bull. Bibl. Storia Sc.

Mat. e Fis., 18, 1885, 468.
^^'Posthumous manuscript, Oeuvres, 10, 298.
i23Meditationes Algebraicae, 1770, 217; ed. 3, 1782, 379. The theorem was ascribed to Waring

by O. Terquem, Nouv. Ann. Math., 18, 1859, Bull. Bibl. Hist., p. 2; by E. Catalan, Bull.

Bibl. Storia Sc. Mat. e Fis., 18, 1885, 467; and by Lucas, Th^orie des Nombres, 1891, 353.
i2^Acta Acad. Petrop., 4, II, 1780 (1775), 38; Comm. Arith. Coll., 2, 1849, 135.

422 History of the Theory of Numbers. [Chap, xviii

A. Desboves^^^ verified that every even number between 2 and 10000 is a
sum of two primes in at least two ways; while, if the even number is the
double of an odd number, it is simultaneously a sum of two piimes of the
form 4n+l and also a sum of two primes of the form 4n — 1.

J. J. Sylvester^ ^^ stated that the number of ways of expressing a very
large even number n as a sum of two primes is approximately the ratio of the
square of the number of primes < n to n, and hence bears a finite ratio to the
quotient of n by the square of the natural logarithm of n. [Cf. Stackel"^].

F. J. E. Lionnet^-' designated by x the number of ways 2a can be
expressed as a sum of two odd primes, by y the number of ways 2a can be
expressed as a sum of two distinct odd composite numbers, by z the number
of odd primes <2a, and by q the largest integer ^a/2. He proved that
q^x = y-\-z and argued that it is very probable that there are values of n
for which q = y-\-z, whence a: = 0.

N. V. Bougaief ^^^" noted that, if M{n) denotes the number of ways n can
be expressed as a simi of two primes, and if Oi denotes the ith. prime >1,

S(n-3^.)ilf(n-^.)=0.

G. Cantor^^^ verified Goldbach's theorem up to 1000. His table gives
the number of decompositions of each even number < 1000 as a sum of two
primes and lists the smaller prime.

V. Aubry^29 verified the theorem from 1002 to 2000.

R. Haussner^^° verified the law up to 10000 and announced results
observed by a study of his^" tables up to 5000. His table I (pp. 25-178)
gives the number v of decompositions of every even n up to 3000 as a sum
x-\-y oi two primes and the values oi x (x^y), as in the table by Cantor.
His table II (pp. 181-191) gives v for 2<n<5000; this table and further
computations enable him to state that Goldbach's theorem is true for
n< 10000. Let P(2p+1) be the number of all odd primes 1, 3, 5, . . . which
are ^2p+l, and set

^(2p+l)=P(2p+l)-2P(2p-l)+P(2p-3), P(-l)=P(-3)=0.

Then the number of decompositions of 2n into a sum of two primes x, y

{x^y) is „_i

S P(2n-2p-l)^(2p+l).

If e = 1 or — 1 according as n is a prime or not,

»/ = iSP(2n-2p-l)^(2p+l)+^-

■1

2

i»Nouv. Ann. Math., 14, 1855, 293.

i"Proc. London Math. Soc, 4, 1871-3, 4-6; CoU. M. Papers, 2, 709-711.

>"Nouv. Ann. Math., (2), 18, 1879, 356. Cf. Assoc, frang. av. ec, 1894, I, p. 96.

""KDomptes Rendus Paris, 100, 1885, 1124.

"'Assoc, fran?. av. sc, 1894, 117-134; rinterm^diaire des math., 2, 1895, 179.

"»L'interm6diaire des math., 3, 1896, 75; 4, 1897, 60; 10, 1903, 61 (errata, p. 166, p. 283).

"•Jahresbericht Deutschen Math.-Verein., 5, 1896, 62-66. Verhandlungen Gesell. Deutscher

Naturforscher u. Aerzte, 1896, II, 8.
»"Nova Acta Acad. Caes. Leop.-Carolinae, 72, 1899, 1-214.

Chap. XVIII] GoLDBACh's THEOREM. 423

Table III gives the values of P and ^ for each odd number 2p+l<5000.
P. StackeP^^ noted that Lionnet's^" argument is not conclusive, and
designated by G2r, the number of all decompositions of 2n as a sum of two
primes (counting p+g and g+p as two different decompositions). If
Pk is the number of all odd primes from 1 to k,

I G2y'^ = {l^x^f = {l-x^Y(%P,^^,:^''A\

where p ranges over all the odd primes. Approximations to G^2n for n large
in terms of Euler's 0-function are

[P(2n- V2n) -P{-V2^)f n

2n

0(2n) n-y/2n <t>{2n)

where P{k) is written for P^ for convenience in printing. Lack of agree-
ment with Sylvester ^2^ is noted; cf. Landau. ^^^ It is stated that the
truth of Goldbach's theorem is made very probable [but not proved^^^].

Sylvester^^^" stated that any even integer 2n is a sum of two primes, one
> n/2 and the other < 3n/2, whence it is possible to find two primes whose
difference is less than any given number and whose sum is twice that number.

F. J. Studnicka^^* discussed Sylvester's statement.

Sylvester^^**" stated that, if N is even and X, . . . , co are the 6 primes > \N
and <fA^ (excluding ^A^" if it be prime), the number of ways of composing
N [by addition] with two of these primes is the coefficient of x^ in

(l^+-+T^)Vr(.-l)r- (rfe2).

E. Landau^^^ noted that Stackel's approximation to G„ is

mn=

n^

log^ n0(n)

and showed that S^=i(t„ has the true approximation ^x^/\o^x. By a longer
analysis, he proved that if we use Stackel's (SJ„ to form the sum, we do not
obtain a result of the correct order of magnitude.

L. Ripert^^^ examined certain large even numbers.

E. Maillet^" proved that every even number ^350000 (or 10^ or 9-10®)
is, in default by at most 6 (or 8 or 14), the sum of two primes.

A. Cunningham^^^ verified Goldbach's theorem for all numbers up to
200 million which are of the forms

(4-3)", (4-5)", 2•10^ 2'»(2"=f1), a-2", 2a", (2a)^ 2(2^=Fa),

for a = 1, 3, 5, 7, 9, 11. He reduced the formula of Haussner for i' to a form
more convenient for computation.

"2G6ttingen Nachrichten, 1896, 292-9. "'Encyclop6die des sc. math., I, 17, p. 339, top.

i33aNature, 55, 1896-7, 196, 269. »"Casopis, Prag, 26, 1897, 207-8.

"40Educ. Times, Jan. 1897. Proof by J. Hammond, Math. Quest. Educ. Times, 26, 1914, 100.

"^Gottingen Nachrichten, 1900, 177-186.

"«L'interm6diaire des math., 10, 1903, 67, 74, 166 (errors, p. 168).

»"/6id., 12, 1905, 107-9. »"Messenger Math., 36, 1906, 17-30.

^

f

424 History of the Theory of Numbers. [Chap, xviii

J. Merlin^^' considered the operation A (6, a) of effacing from the natural
series of integers all the numbers ax-\-b. The effect of carrying out one of
the two sets of operations A{ri, pi), ^(r,-, p,), A{r'i, pi), i = 2,. . ., n, where
p„ is the nth prime > 1, is equivalent to constructing a crib of Eratosthenes
up to p„. It is stated that in every interval of length vp^ log p„ there is at
least one number not effaced, if v is independent of n. It is said to follow
that, for a sufficiently large, there exist two primes having the sum 2a.
Under specified assumptions, there exist an infinitude of n's for which
Pn+i-Pn = 2.

M. Vecchi^*° wrote Pn for the nth odd prime and called p^ and p/,+„ of
the same order if p^h>Ph+a- Then 2n> 132 is a sum of two primes of the
same order in [K0+1)] ways if and only if there exist </> numbers not
> /I — p^+i + 1 and not representable in any of the forms

Gi+Sx, bi+5x,..., li+PmX (i=l, 2),

where p^+i is the least prime p for which p'^-\-p> 2n, and the known terms a.,
. . . are the residues with respect to the odd prime occurring as coefficient of x.
*G. Giovannelli, Sul teorema di Goldbach, Atri, 1913.

Theorems Analogous to Goldbach's.

Chr. Goldbach ^^^ stated empirically that every odd number is of the
form p-\-2a^, where p is a prime and a is an integer ^ 0. L. Euler^^^ verified
this up to 2500. Euler^24 verified for m = 8iV+3^ 187 that m is the sum
of an odd square and the double of a prime 4n+l.

J. L. Lagrange ^"^^ announced the empirical theorem that every prime
4n — 1 is a sum of a prime 4?n + l and the double of a prime 4/i + l.

A. de Polignac^^^ conjectured that every even number is the difference
of two consecutive primes in an infinitude of ways. His verification up
to 3 million that every odd number is the sum of a prime and a power of
2 was later "^^ admitted to be in error for 959.

M. A. Stern^^^ and his students found that 53-109 = 5777 and 13-641
= 5993 are neither of the form p-\-2a^ and verified that up to 9000 there are
no further exceptions to Goldbach's^'*^ assertion. Also, 17, 137, 227, 977,
1187 and 1493 are the only primes <9000 not of the form p+26^ 6>0.
Thus all odd numbers <9000, which are not of the form 6n+5, are of the
form p+26^.

E. Lemoine^^'' stated empirically that every odd number >3 is a sum
of a prime p and the double of a prime tt, and is also of the forms p — 2Tr
and 27r' — p'.

'"Comptes Rendus Paris, 153, 1911, 516-8. Bull. des. sc. math., (2), 39, I, 1915, 121-136. In

a prefatory note, J. Hadamard noted that, while the proof has a lacuna, it is suggestive.
""Atti Reale Accad. Lincei, Rendiconti, (5), 22, II, 1913, 654-9.
'"Corresp. Math. Phys. (ed.. Fuss), 1, 1843, 595; letter to Euler, Nov. 18, 1752.
»«/W<i., p. 596, 606; Dec. 16, 1752.

"'Nouv. M6ni. Ac. Berlin, ann6e 1775, 1777, 356; Oeuvres, 3, 795.
"8Nouv. Ann. Math., 8, 1849, 428 (14, 1855, 118).
»«»''Comptes Rendus Paris, 29, 1849, 400, 738-9.
"»Nouv. Ann. Math., 15, 1856, 23. ""L'interm^diaire des math., 1, 1894, 179; 3, 1896, 151

Chap. XVIII] PRIMES IN ARITHMETICAL PROGRESSION. 425

H. Brocard^^^ gave an incorrect argument by use of Bertrand's postulate
that there exists a prime between any two consecutive triangular numbers.

G. de Rocquigny^^^ remarked that it seems true that every multiple of
6 is the difference of two primes of the form 6n+l.

Brocard^^^ verified this property for a wide range of values.

L. Kronecker^^^ remarked that an unnamed writer'^^ had stated empiri-
cally that every even number can be expressed in an infinitude of ways as
the difference of two primes. Taking 2 as the number, we conclude that
there exist an infinitude of pairs of primes differing by 2.

L. Ripert^^^ verified that every even number < 10000 is a sum of a prime
and a power, every odd one except 1549 is such a sum.

E. Maillet^^^ commented on de Polignac's conjecture that every even
number is the difference of two primes.

E. Maillet^" proved that every odd number < 60000 (or 9-10^) is, in
default by at most 8 (or 14), the sum of a prime and the double of a prime.

Primes in Arithmetical Progression.

E. Waring^^^ stated that if three primes (the first of which is not 3) are
in arithmetical progression, the common difference d is divisible by 6,
except for the series 1, 2, 3 and 1, 3, 5. For 5 primes, the first of which is
not 5, d is divisible by 30; for 7 primes, the first not 7, d is divisible by
2-3-5-7; for 11 primes, the first not 11, d is divisible by 2-3-5-7-11; and
similarly for any prime number of primes in arithmetical progression, a
property easily proved. Hence by continually adding d to a prime, we
reach a number divisible by 3, 5, ... , unless d is divisible by 3, 5, . . . .

J. L. Lagrange ^^"^ proved that if 3 primes, no one being 3, are in arith-
metical progression, the difference d is divisible by 6; for 5 primes, no one
being 5, d is divisible by 30. He stated that for 7 primes, d is divisible by
2-3-5'7, unless the first one is 7, and then there are not more than 7 consecu-
tive prime terms in a progression whose difference is not divisible by 2-3 -5 -7.

E. Mathieu^^^ proved Waring's statement.

M. Cantor^ ®^ proved that if P = 2-3. . .p is the product of all the primes
up to the prime p, there is no arithmetical progression of p primes, no one
of which is p, unless the common difference is divisible by P. He conjec-
tured that three successive primes are not in arithmetical progression unless
one of them is 3.

A. Guibert^®^ gave a short proof of the theorem stated thus: Let
Pi,...,Pn be primes ^ 1 in arithmetical progression, where n is odd and >3.
Then no prime >1 and ^n is a Pi. If n is a prime and is a pi, then i = l.

i"L'intermediaire des math., 4, 1897, 159. Criticism by E. Landau, 20, 1913, 153.

is^/feid., 5, 1898, 268. i^L'intermediaire des math., 6, 1899, 144.

i64Vorlesungen iiber Zahlentheorie, 1, 1901, 68.

i«L'interm6diaire des math., 10, 1903, 217-8. i"/6td., 12, 1905, 108.

^"Ibid., 13, 1906, 9. i«*Meditationes Algebraicae, 1770; ed. 3, 1782, 379.

i««Nouv. M6m. Ac. Berlin, ann^e 1771, 1773, 134-7. »"Nouv. Ann. Math., 19, 1860, 384-5.

"sZeitschrift Math. Phys., 6, 1861, 340-3.

"»Jour. de Math., (2), 7, 1862, 414-6.

426 History of the Theory of Numbers. [Chap, xviii

The common difference is divisible by each prime ^n, and by n itself if n is
a prime not in the series.

H. Brocard^^^" gave several sets of five consecutive odd integers, four of
which are primes. Lionnet^^^** had asked if the number of such sets is un-
limited.

G. Lemaire^^° noted that 7+30n and 107+30/1 (n = 0, 1,. . ., 5) are all
primes; also 7 + 150/1 and 47+210m (n = 0, . . ., 6).

E. B. Escott^^^ found conditions that a+210M (n = 0, 1,. . ., 9) be all
primes and noted that the conditions are satisfied if a = 199.

De\'ignot^" noted the primes 47+210«, 71+2310?i (n = 0, 1,. . ., 6).

A. Martin^^^ gave numerous sets of primes in arithmetical progression.

Tests for Primality.

The fact that n is a prime if and only if it divides 1 + (n — 1) ! was noted
by Leibniz/ Lagrange, ^^ Genty,-^ Lebesgue,^^ and Catalan/^^ cited in Chap-
ter III, where was discussed the converse of Fermat's theorem in furnishing
a primality test. Tests by Lucas, etc., were noted in Ch. XVII. Further
tests have been noted under Cipolla^" and^'^ Cole^" of Ch. I, Sardi"^ of
Ch. Ill, Lambert^ of Ch. VI, Zsigmondv"^ of Ch. VII, Gegenbauer^o- »2 ^f
Ch. X, Jolivald^ of Ch. XIII, Euler,^^^ Tchebychef,"^ Schaffgotsch^""^ and
Biddle^^^ of Ch. XIV, Hurwitz" and CipoUa^^ of Ch. XV. See also the
papers by von Koch,^^^ Hayashi,^^' ^° Andreoli,^"^ and Petrovitch^ of the
next section.

L. Euler^^^ gave a test for the primality of a number N = 4:m-\-l which
ends with 3 or 7. Let R be the remainder on subtracting from 2N the next
smaller square (5n)- which ends with 5. To R add 100(n — 1), 100(n — 3),
100(n — 5), .... If among R and these sums there occurs a single square,
iV is a prime or is divisible by this square. But if no square occurs or if
two or more squares occur, A^ is composite. For example, if A = 637,
(5n)2 = 1225, R = 49; among 49, 649, 1049, 1249 occurs only the square 49;
hence A^ is a prime or is di\asible by 49 [A = 49- 13].

W. L. Kraft^"^ noted that Qin + 1 is a prime if m is of neither of the forms
Qxy=^{x+y); 6?m — 1 is a prime if m9^6xy+x — y.

A. S. de Montferrier^'^ noted that an odd number A is a prime if and
only if A-\-k' is not a square for A: = 1, 2, . . ., (A — 3)/2.

AI. A. Stern^^° noted that n is a prime if and only if it occurs n — 1 times
in the (n — l)th set, where the first set is 1, 2, 1; the second set, formed by
inserting between any two terms of the first set their sum, is 1, 3, 2, 3, 1 ; etc.

"'"Xouv. Ann. Math., (3), 15, 1896, 389-90. i696Nouv. Ann. Math., (3), 1, 1882, 336.

""L'intcrraddiaire des math., 16, 1909, 194-5.

"'Ibid., 17, 1910, 285-6.

"*Jbid., 4.5-6. ^"School Science and Mathematics, 13, 1913, 793-7,

'"*Doubt as to the suflBciency of Cole's test has been expressed, Proc. London Math. Soc, (2).

16, 1917- 8. i"Opera postuma, I, 188-9 (about 1778).

"»\ova Acta Acad. Petrop., 12, 1801, hist., p. 76, mem., p. 217.
"•Corresp. Math. Phys. (ed., Quetelet), 5, 1829, 94-6.
""Jour, fiir Math., 55, 1858, 202.

1

Chap. XVIII] Tests FOR Primality. - 427

L. Gegenbauer^^^ noted that 4n+l is a prime if

L 4i/ J"L 4?/ J

for every odd y, 1<?/^ V4n+1, and gave two similar tests for 4n+3.

D. Gambioli^^^ and O. Meissner^^^ discussed the impracticabiUty of the
test by the converse of Wilson's theorem.

J. Hacks^^^ gave the characteristic relations for primes p:

K. Zsigmondy^^^ noted that a number is a prime if and only if not
expressible in the form aia2+i3i/32, where the a's and j3's are positive integers
such that ai+a2=7/3i— 1S2. An odd number C is a prime if and only if
C-\-k^ is not a square for k = 0, 1,. . ., [(C-9)/6].

R. D. von Sterneck^^^" gave several criteria for the (s + l)th prime by use
of partitions into elements formed from the first s primes.

H. Laurent^^^* noted that

equals 0 or 1 according as z is composite or prime.

Fontebasso^^® noted that A^ is a prime if not divisible by one of the
primes 2, 3, . . ., p, where iV/p<p+4.

H. Laurent ^^^ proved that if we divide

Fnix) = n\l -a:0(l -x^^) . . . (1 -x^""^'-'')

3 = 1

by (x" — l)/(a: — 1), the remainder is 0 or n"~^ according as n is composite or
prime. If we take a: to be an imaginary root of a;" = 1, Fn{x) becomes 0 or
n"~^ in the respective cases.

Helge von Koch^^^ used infinite series to test whether or not a number is a
power of a prime.

Ph. Jolivald^^^ noted that, since every odd composite number is the
difference of two triangular numbers, an odd number iV is a prime if and
only if there is no odd square, with a root ^ (2iV — 9)/3, which increased by
8A^ gives a square.

S. Minetola^^" noted that, if k—n is divisible by 2n + l, then 2A;+1 is
composite. We may terminate the examination when we reach a prime
2n+l for which {k-n)/{2n+l)^n.

A. Bindoni^^^ added that we may stop with a prime giving (k—n)

isiSitzungsber. Ak. Wiss. Wien (Math.), 99, Ila, 1890, 389.

is^Periodico di Mat., 13, 1898, 208-212. '"Math. Naturw. Blatter, 3, 1906, 100

>8*Acta Mathematica, 17, 1893, 205. ""Monatsh. Math. Phys., 5, 1894, 123-8.

"S'^Sitzungsber. Ak. Wiss. Wien (Math.), 105, Ila, 1896, 877-882.

iss^Comptes Rendus Paris, 126, 1898, 809-810. "^guppj^ Periodico di Mat., 1899, 53.

i"Nouv. Ann. Math., (3), 18, 1899, 234-241.

"sOfversigt Veten.-Akad. Forhand., 57, 1900, 789-794 (French).

"9L'interm4diaire des math., 9, 1902, 96; 10, 1903, 20.

""11 Boll. Matematica Giorn. Sc.-Didat., Bologna, 6, 1907, 100-4. i"/6td., 165-6.

428 History of the Theory of Numbers. [Ch.u'. xviii

-^ (2n+l)^n+2a — 1, where a is the difiference between 2/1+1 and the next
greater prime.

F. Stasi^^- noted that iV is a prime if not divisible by one of the primes
2, 3, . . ., p, where N/p<p-\-2a and a is the difference between p and the
prime just >p.

E. Zondadari^^^ noted that

Sin-TTX * TTX

(7rx)^(l— x^)^n=2W sin irx/n

is zero when j = ± p (pa prime) and not otherwise.

A. Chiari'^"* cited known tests for primes, as the converse of Wilson's
theorem.

H. C. PockHngton^^^ employed single valued functions (}>(x), rp(x),
vanishing for all positive integers a: (as 0 = i/' = sin ttx), and real, finite and not
zero for all other positive values of x. Then, for the gamma function F,

^.(,)+^.(i±IM)

is zero if and only if x is a prime [Wigert^^^"].

E. B. Escott^^^ stated that if we choose ai, . . . , a„, b so that the coeflBicients
of x^", x^"~^, . . . , a:^ in the expansion of

(x"+aix'*-^+...+aj2(x+5)

are all zero, then all the remaining coefficients, other than the first and last,
are divisible by 2?i + l if and only if 2/i + l is a prime.

J. de Barinaga^^^ concluded from Wilson's theorem that if (P — 1)! is
divided by 1+2+ . . . +(P-1) =P(P-l)/2, the remainder is P-1 when P
is a prime, but is zero when P is composite (not excluding P = 4 as in the con-
verse of Wilson's theorem). Hence on increasing by unity the least positive
residues ?^0 obtained on di\'iding 1-2. . .x by 1+2+ . . . +x, for x= 1, 2,
3, . . . , we obtain the successive odd primes 3, 5, ... .

M. Vecchi^^° noted that, if x^ 1, A^>2 is a prime if and only if it be of
the form 2^'— tt, where tt is the product of all odd primes ^p, p being
the largest odd primed [\/iV], and where tt' is a product of powers of
primes >p with exponents ^0. Again, A^> 121 is a prime if and only if of
the form tt — 2V where y^l.

Vecchi^^^ gave the simpler test: A^>5 is a prime if and only ii a—^=N,
a+j8 = 7r, for a, /3 relatively prime, where tt is the product of all the odd
primes ^[VA'']-

G. Rados^^^ noted that p is a prime if and only if {2!3! . . . (p — 2)!
(p-l)!j4=i(modp).

CarmichaeP^ gave several tests analogous to those by Lucas.

i«Il Boll. Matiraatica Giorn. Sc.-Didat., Bologna, 6, 1907. 120-1.

"'Rend. Accad. Lined, (5), 19, 1910, 1, 319-324. i»^Il Pitagora, Palermo, 17, 1910-11, 31-33.

"*Proc. Cambr. Phil. Soc., 16, 1911, 12. »»«L'interm6diaire des math., 19, 1912, 241-2.

"'Revista de la Sociedad Mat. Espanola, 2, 1912, 17-21.

"»Periodico di Mat., 29, 1913, 126-8. "»Math. 6s Term^s firtesito, 34, 1916, 62-70"

i

Chap. XVIII] NUMBER OF PRIMES. 429

Number of Primes Between Assigned Limits.

Formula (5) of Legendre in Ch. V implies that if 0, X, . . . are the primes
= Vn, the mimber of primes ^ n and > Vn is one less (if unity be counted a
prime) than

statements or proofs of this result have been given by C. J. Hargreave,^^*
E. de Jonquieres,206 R. Lipschitz,207 j. j. Sylvester,^^^ E. Catalan,^^^ F. Ro-

gel,^^° J. Hammond^^^ with a modification, H. W. Curjel,^^^" S. Johnsen,^^^
and L. Kronecker.^^^

E. MeisseP^'* proved that if d{m) is the number of primes (including
unity) ^m and if

*(P.- . . . p."") = ( - 1)-+ •+"" ("■+"^+- •■+»»)!,

rill. . .n-f

1

.$(l)^[f]+<i.(2)e[f] + ...+*Wflg].

E. MeisseP^^ wrote $(m, n) for Legendre's formula for the number of
integers ^ m which are divisible by no one of the first n primes pi = 2, . . . , p„.
Then .p^-, x

<l>(m, n) =^{m, n — 1) — «l> ( — , n — 1 j •

Let^(m)be the number of primes ^m. Setn+fx = d{\/m),n==d{^^/m). Then

e{m)=^{m, n)+n(M+l)+^^^~'^^-l- i d(^^),

which is used to compute Birri) for m = ^-10^, A; = 1/2, 1, 10.

MeisseP^^ applied his last formula to find ^(10^).

Lionnet^^^'' stated that the number of primes between A and 2 A is
<B{A).

N. V. Bougaief2i7 obtained from Q{n) +^(n/2) +^(V3) + • • • =S[n/p], by
inversion (Ch. XIX),

^(^) =49 -^4^] +«4J^] - -45] +4Je] -<^c] + • ■ • .

where a, h,. . . range over all primes.

2«6Lond. Ed. Dub. Phil. Mag., (4), 8, 1854, 118-122.

^o^Comptes Rendus Paris, 95, 1882, 1144, 1343; 96, 1883, 231.

^oUbid., 95, 1882, 1344-6; 96, 1883, 58-61, 114-5, 327-9.

2<>876id., 96, 1883, 463-5; Coll. Math. Papers, 4, p. 88.

2°9Mem. Soc. Roy. Sc. de Liege, (2), 12, 1885, 119; Melanges Math., 1868, 133-5.

JioArchiv Math. Phys., (2), 7, 1889, 381-8. ^iiMessenger Math., 20, 1890-1, 182.

2"«Math. Quest. Educ. Times, 67, 1897, 27.

"2Nyt Tidsskrift for Mat., Kjobenhavn, 15 A, 1904, 41^.

2"Vorlesungen uber Zahlentheorie, I, 1901, 301-4. "ujour. fur Math., 48, 1854, 310-4.

2i5Math. Ann., 2, 1870, 636-642. Outline in Mathews' Theory of Numbers, 273-8, and in G.

Wertheim's Elemente der Zahlentheorie, 1887, 20-25.
2i676id., 3, 1871, 523-5. Corrections, 21, 1883, 304.
2i6aNouv. Ann. Math., 1872, 190. Cf. Landau, (4), 1, 1901, 281-2.
21'Bull. sc. math, astr., 10, 1, 1876, 16. Mat. Sbomik (Math. Soc. Moscow), 6, 1872-3, I, 180.

430

History of the Theory of Numbers.

[Chap. XVIII

N,

P. de Mond^sir-^^ wrote Np for the number of multiples of the prime p
which are < 2.V and divisible by no prime < p. Then the number of primes
<2.V is N—1iNp-\-n-\-l, where n is the number of primes <y/2N. Also,

.p\ Lapj LahpA '

where a, h,. . . are the primes <p. By this modification of Legendre's
formula, he computed the number 78490 of primes under one million.

*L. Lorenz-^^ discussed the number of primes under a given limit.

Paolo Paci"'' proved that the number of integers ^n divisible by a
prime <\/ri is

where r, s,. . . range over all the H primes 2, 3, . . . , p less than \/n. Thus
there are n — \ —N-\-H primes from 1 to n. The approximate value of N is

</>(2-3...p)"

y r rs } y 2-3... p J

Vs"^'J '\S 2-3... p

K. E. Hoffmann--^ denoted by N the number of primes <m, by X the
number of distinct prime factors of tw, by ^i the number of composite integers
<m and prime to m. Evidently N = 4>{M) — ii-\-\. To find A'' it suffices
to determine ix. To that end he would count the products <mhy twos,
by threes, etc. (with repetitions) of the primes not dividing m.

J. P. Gram-" proved that the number of powers of primes ^n is

[Cf. Bougaief.^^^] Of the two proofs, one is by inversion from

E. Cesaro^^ considered the number x of primes ^qn and >n, where
g is a fixed prime. Let coi, . . . , co, be the primes ^ n other than 1 and q.
Let5*^n<g*+\ Then

Let Ir,, be the number of the [qn/{o3i . . .co,)] which give the remainder r when
divided by q. Set t, = 'Ljlj,,. Then

x=(k+l)q-{k + 2)-U + t2-h+ . . ..

"'Assoc, frang. av. sc, 6, 1877, 77-92. Nouv. Corresp. Math., 6, 1880, 256.

«»Tidsskr. for Math., Kjobenhavn, (4), 2, 1878, 1-3.

""Sul numero de numeri primi inferiori ad un dato numero, Parma, 1879, 10 pp.

»"Archiv Math. Phys., 64, 1879, 333-6.

«K. Danake Vidensk. Selskabs. Skrifter, (6), 2, 1881-6, 183-288; r6sum6 in French, 289-308.

See pp. 220-8, 296-8.
»M6m. Soc. Sc. Li^e, (2), 10,«1883, 287-8.

Chap. XVIII] NuMBER OF PRIMES. 431

E. Catalan^^'* obtained the preceding results for the case g = 2; then ti is
the number of odd quotients [2n/(8], (2 the number of odd quotients
[2n/{^y)], . . . , where I3,y,. . . are the primes >2 and ^n.

L. Gegenbauer225 gave eight formulas, (29)-(36), of the type of
Legendre's, a special case of one being

([^])/^(^) = 1+L,(n), SM^^^ t\

where x ranges over the integers divisible by no prime > Vn, while fi(x) is
Merten's function (Ch. XIX) and Lh{n) is the sum of the kth. powers of all
primes >\/n but Sn. The case A; = 0 is Legendre's formula. The case
A; = l is Sylvester's^"^

E. MeisseP^^ computed the number of primes < 10^
Gegenbauer-^*^" gave compUcated expressions for d{n), one a generaliza-
tion of Bougaief's.^^'^

A. Lugli^" wrote 4>{n, i) for the number of integers ^n which are divis-
ible by no one of the first i primes Pi = 2, p2 = 3, . . . . If 2; is the number of
primes S -y/n and if s is the least integer such that

the number \l/{n) of primes ^n, excluding 1, is proved to satisfy

This method of computing \l/{n) is claimed to be simpler than that by
Legendre or Meissel.

J. J. van Laar^"" found the number of primes < 30030 by use of the
primes <1760.

C. Hossfeld^^^ gave a direct proof of

^{gVi- ■ ■Pn=^r,n)==g{pi-l). . .(p„-l)±$(r, n),

the case of the upper signs being due to Meissel. ^^^

F. Rogel"^^ gave a modification and extension of Meissel's^^^ formula.
H. Scheffler^^'' discussed the number of primes between p and q.
J. J. Sylvester^^^ stated that the number of primes >n and <2n is

a ab abc

ii a,h,. . . are the primes ^ \/2n and Hx denotes x when its fractional part

224Mem. Soc. Sc. Lidge, M6m. No. 1.

225Sitzungsber. Ak. Wiss. Wien (Math.), 89, II, 1884, 841-850; 95, II, 1887, 291-6.
22«Math. Annalen, 25, 1885, 251-7.

""ositzungsber. Ak. Wiss. Wien (Math.), 94, II, 1886, 903-10.
'"Giornale di Mat., 26, 1888, 86-95.
227aNieuw Archief voor Wisk., 16, 1889, 209-214.
=28Zeitschrift Math. Phys., 35, 1890, 382-i.

22»Math. Annalen, 36, 1890, 304-315. ^'OBeitrage zur Zahlentheorie, 1891, 187.

"iLucas, Th^orie des nombres, 1891, 411-2. Proof by H. W. Curjel, Math. Quest. Educ.
Times, 57, 1892, 113.

432 History of the Theory of Numbers. [Chap, xviii

is 1/2, but the nearest integer to x in the contrary case. L. Gegenbauer^^^*
gave a proof and generalization.

Sylvester-^ ^'' noted that, if din) is the number of primes ^u, and if
pi , . . . , Pi be the primes ^ \/x, and gi, . ,gy those between \/x and x, then

xd(x/p)-m^'/q)= {e{Vx)\\

H. W. Curjel'-^^" noted that the number of primes >p and <p- is ^p
if p is a prime ^5. We have only to delete from 1, 2, . . ., p^ multiples of
2, 3, 5, . . . , or p.

L. Gegenbauer-^- considered the integers x divisible by no square and
formed of the odd primes ^m, when n^w^\/2n. Of the numbers [2«/x]
which are of one of the forms 4s +1 and 4s +2, count those in which x is
formed of an even number of primes and those in which x is formed of an
odd number; denote the difference of the counts by a. He stated that the
interv^al from m + 1 to n (limits included) contains a — 1 more primes than the
inter\'al from tz+I to 2n.

He gave (pp. 89-93) an expression for the sum of the values taken by an
arbitrary- function g(x) when x ranges over the primes among the first n
terms of an arithmetical i)rogression; in particular, he enumerated the
primes ^n of the form 4s +1 or 4s — 1.

F. Graefe-^^ would find the number of primes <m = 10000 by use of
tables showing for each prime p, 5'^p^\/m, the values of n for which
6n+l or 6nH-5 is divisible by p.

P. Bachmann-^ quoted de Jonquieres,^°^ Lipschitz,-°^ Sylvester,2°^ and
Ces^ro."^

H. von Koch235 wrote f{x) = (a:-l)(a:-2) . . . (x-n),

fix)

X=2L A J t..^=2{x-IJLv)f'{t^v)

0(a:)=njl-^j, p{x)= 2 ,, •;.:;;,..,., (fxvSn),

and proved that, for positive integers x^n, d(x) = 1 or 0 according as x is
prime or composite. The number of primes ^m^n is ^(1)+. . .+^(m).
A. Baranowski-^^ noted the formula, simpler than Meissel's,^^^

xP{n)=<l>[n, ^(v^)]H-^(v^) -1

for computing the number \f/(n) of primes ^n.

S. Wigert^^^^ noted that the number of primes < n is

1 Cf'{x)dx , ., . . 2 , . o /i+r(x)\

TT^ I ./ X , where /(x) =smVx+sm-7r I ),

2TnJ f{x) \ X /

"'"Denkschr. Akad. Wiss. Wien (Math.), 60, 1893, 47.

"i^Math. Quest. Educ. Times, 56, 1892, 67-8.

"'olbid., 58, 1893, 127.

"^Monatshefte Math. Phys., 4, 1893, 98.

'"Zeitschrift Math. Phys., 39, 1894, 38-50.

»»<Die Analytische Zahlentheorie, 1894, 322-5.

"*Comptes Rendus Paris, 118, 1894, 850-3.

"•Bull. Int. Ac. Sc. Cracovie, 1894, 280-1 (German). Cf. ♦Rozpraw'y Akad. Umiej., Cracovie,

(2), 8, 1895, 192-219.
'"''Ofversigt K. Vetensk. Ak. Forhand., Stockhohn, 52, 1895, 341-7.

I

Chap. XVIII] NuMBER OF PRIMES. 433

since the only real zeros of f{x) are the primes. The integration extends
over a closed contour enclosing the segment of the a;-axis from 1 to n and
narrow enough to cofitain no complex zero of /(x).

T. Levi-Civita^^^^ gave an analytic formula, involving definite integrals
and infinite series, for the number of primes between a and /3.

L. Gegenbauer^" gave formulas, similar to that by von Koch,^"^ for the
number of primes 4s ±1 or 6s ±1 which are ^n.

A. P. Minin^^'^'' wrote ^{y)=0 or 1 according as y is composite or prime;

*^®° e{n-l) = [n-2] + [n-b] + [n-7]+ . . .-^^P{x-\)[n-x],
summed for all composite integers x.

Gegenbauer^"'' proved that Sylvester's^^^ expression for the number of
primes >n and <2n equals S)u(x)[m/a:+l/2], where x takes those integral
values S 2n which are products of primes S y/2n.

F. RogeP^^ gave a recursion formula for the number of primes ^m.

T. Hayashi^^^ wrote Rf/q for the remainder obtained on dividing / by q.
By Laurent's^^'^ result, —RFn{x)/{x'' — l)rf'~^ = 0 or 1 according as n is
composite or prime. Hence the sum of the jth powers of the primes between

.andHs _j,;__FM__

nt.(a:"-l)n"-^-2'
which becomes the number of primes for j = 0. If a is a primitive nth root
of unity, Wilson's theorem shows that

n-l

Sa^"^ = norO (m = (n-l)! + l),

; = 0

according as n is prime or composite. Hence ^x^"~^^7(a:"— 1) = 1 or 0
according as n is prime or composite. Thus

^2a;("-i)y(a;'»-l)

n = s

is the number of primes between s and t.

Hayashi^^" reproduced the second of his two preceding results and gave
it the form

J"^^"^ „ ^ \ cos (m—n)d — r''cos md\dd ^
„ '• l-2r''cosng+r^' =^" " «'

according as n is prime or not, and gave a direct proof.

J. V. Pexider^^^ investigated the number \l/{x) of primes ^ x. Write

4g=G]-[^]' ^"-[f]-

"«&Atti R. Accad. Lincei, Rendiconti, (5), 4, 1895, I, 303-9.

"'Monatshefte Math. Phys., 7, 1896, 73.

2"aBull. Math. Soc. Moscow, 9, 1898, No. 2; Fortschritte, 1898, 165.

2376Monatshefte Math. Phys., 10, 1899, 370-3.

238Archiv Math. Phys., (2), 17, 1900, 225-237.

«9Jour. of the Phys. School in Tokio, 9, 1900; reprinted in Abhand. Gesch. Math. Wiss., 28,

1900, 72-5.
»^oArchiv Math. Phys., (3), 1, 1901, 246-251.
2«Mitt. Naturforsch. Gesell. Bern, 1906, 82-91.

434

History of the Theory of Numbers.

[Chap. XVIII

Hence the number of integers ^x which are divisible by a, but not by
a-1, a-2,. . ., 2, is

[x/a] a-1

(7„=s n(i-3,).

k=ln=2

The number ^(a:), of primes ^x and >v = [\/^] is [x]-l-2°Z20-,. Let
Pi,. . ., Pa be the primes ^ \/a- Let p^ be the greatest prime ^ v. Then

<,(,)+i=M_[|]_jTn{i-A[^]},

from which follows Legendre's formula.

S. Minetola-^- obtained a formula to compute the number of primes
^K = 2k + l, not presupposing a knowledge of any primes >2, by consid-
ering the sets of positive integers n, n',. . . for which

(2n + l)(2n' + l)^K, (2n + l)(2n' + l)(2n" + l)^i^,. . ..

F. RogeP^^ started with Legendre's formula for the number A{z) of
primes ^z, introduced the remainders t—\t\, and wrote i?„(z) for the sum
of these partial remainders. He obtained relations between values of the
^'s and ^'s for various arguments z, and treated sums of such values. For
arbitrary x's (p. 1815),

Pn+l-l

p=i
summed for the primes p between 1 and the nth prime p„. By special
choice of the x^s, we get formulas involving Euler's ^-function (p. 1818),
and the number or sum of the divisors of an integer. See RogeP^ of Ch. XL

G. Andreoli^^ noted that, if x is real, and F is the gamma function,

^(x) = sin

2(r(a:) + l)7r

■sinVx

is zero if and only if a: is a prime. Hence the number of primes < n is

1 r''^'{x)dx
2TnX . ^ix)
The sum of the A:th powers of the primes <n is given asymptotically.
M. Petrovitch^"*^ used a real function d{x, u), like

a cos 27ra;+6 cos 2Tru — a — h,

which is zero for every pair of integers x, u, and not if a: or w is fractional.
Let$(x) be the function obtained from d{x, u) by taking

u=\\+nx)]/x.
Thus y=^{x) cuts the a:-axis in points whose abscissas are the primes.

"=Giornale di Mat., 47, 1909, 305-320.

»«Sitzung8ber. Ak. Wiss. Wien (Math.), 121, 1912, Ila, 1785-1824; 122, 1913, II a, 669-700.

"^Rendiconti Accad. Lincei, (5), 21, II, 1912, 404-7. Wigert.'''*''

*«Nouv. Ann. Math., (4), 13, 1913, 406-10.

Chap. XVIII] BeRTRAND's POSTULATE. 435

E. Landau^''^ indicated errors in rintermediaire des math^maticiens on
the approximate number of primes ax+h<N.

*M. Kossler-^^ discussed the relation between Wilson's theorem and the
number of primes between two limits.

See Cesaro^^ of Ch. V, Gegenbauer^^ ^f qj^ ^I, and papers 62-81 of
Ch. XIII.

Bertrand's Postulate.

J. Bertrand^®" verified for numbers < 6 000 000 that for any integer
n>6 there exists at least one prime between n — 2 and n/2.

P. L. Tchebychef^" obtained Hmits for the sum d{z) of the natural
logarithms of all primes ^z and deduced Bertrand's postulate that, for
x>3, there exists a prime between x and 2x — 2. His investigation shows
that for every e> 1/5 there exists a number ^ such that for every x^^ there
exists at least one prime between x and (l + e)x.

A. Desboves,^^^ assuming an unproved theorem of Legendre's,^^ con-
cluded the existence of at least two primes between any number >6 and
its double, also between the squares of two consecutive primes; also at
least p primes between 2n and 2n — k for p and k given and n sufficiently
large, and hence between a sufficiently large number and its square.

F. Proth^^^ claimed to prove Bertrand's postulate.
J. J. Sylvester264 reduced Tchebychef's e to 0.16688.

L. Oppermann-^^ stated the unproved theorem that if n>l there exists
at least one prime between n{n — l) and n^, and also between n^ and n(n+l),
giving a report on the distribution of primes.

E. C. Catalan^^^ proved that Bertrand's postulate is equivalent to

n\ n\

>a''/5^..7^^

where a, . . . , tt denote the primes S n, while a is the number of odd integers
among [2n/a], [2n/a^],..., h the number among [2n/^], [2n//3^],. . .. He
noted (p. 31) that if the postulate is applied to 6 — 1 and 6+1, we see the
existence between 26 and 46 of at least one even number equal to the sum
of two primes.

J. J. Sylvester^" reduced Tchebychef's e to 0.092; D. von Sterneck^^^
to 0.142.

24«L'intermediaire des math., 20, 1913, 179; 15, 1908, 148; 16, 1909, 20-1.

2"Casopis, Prag, 44, 1915, 38-42.

^^ojour. de I'ecole roy. polyt., cah. 30, tome 17, 1845, 129.

2"M^m. Ac. Sc. St. Petersbourg, 7, 1854 (1850), 17-33, 27; Oeuvres, 1, 49-70, 63. Jour, de

Math., 17, 1852, 366-390, 381. Cf. Serret, Cours d'algebre sup^rieure, ed. 2, 2, 1854,

587; ed. 6, 2, 1910, 226.
262NOUV. Ami. Math., 14, 1855, 281-295.
2"Nouv. Corresp. Math., 4, 1878, 236-240.
2«^Amer. Jour. Math., 4, 1881, 230.
2660versigt Videnskabs Selsk. Forh., 1882, 169.

»««M6m. Soc. R. Sc. Liege, (2), 15, 1888 ( = M61anges Math., Ill), 108-110.
26'Messenger Math., (2), 21, 1891-2, 120.
268Sitzungsb. Akad. Wiss. Wien, 109, 1900, II a, 1137-58.

436 History of the Theory of Numbers. [Chap, xvill

T. J. Stieltjes stated and E. Cahen'^^^ proved that we may take e to be
any positive number however small, since d{z) is asjTnptotic^^^"® to z.

H. Brocard"" stated that at least four primes lie between the squares
of two consecutive primes, the first being >3. He remarked that this and
the similar theorem by Desboves-^- can apparently be deduced from Ber-
trand's postulate; but this was denied by E. Landau. ^^^

E. ^laillet^^- proved there is at least one prime between two consecutive
squares <9-10^ or two consecutive triangular numbers ^9-10^.

E. Landau"*^ (pp. 89-92) proved Bertrand's postulate and hence the
existence of a prime between x (excl.) and 2x (incl.) for every x^l.

A. Bonolis-"^ proved that, if x>13 is a number of p digits and a is the
least integer >x/{lO{p-{-l)], there exist at least a primes between x and
[-|x — 2], which implies Bertrand's postulate. If x>l3 is a number of
p digits and /3 is the greatest integer <x/(3p— 3), there are fewer than
^ primes from a: to [-|x — 2].

Miscellaneous Results on Primes.

H. F. Scherk^^*^ stated the empirical theorems: Every prime of odd
rank (the nth prime 1, 2, 3, 5, . . . being of rank n) can be composed by
addition and subtraction of all the smaller primes, each taken once; thus

13 = 1+2-3-5+7+11 = -1+2+3+5-7+11.

Every prime of even rank can be composed similarly, except that the next
earlier prime is doubled; thus

17 = 1+2-3-5+7-11+2-13= -1-2+3-5+7-11+2-13.

Marcker^^^ noted that, if a, 6, . . . , m are the primes between 1 and A
and if p is their product, all the primes from A to A^ are given by

K^?+ ■+^>+»)'

and each but once if each numerator is positive and less than its denominator.

0. Terquem"^- noted that the primes <rr are the odd numbers not
included in the arithmetical progressions q^, q^-\-2q, 5^+4g, . . . up to n^,
for g = 3, 5, . . ., n — 1.

H. J. S. Smith-^^ gave a theoretical method of finding the primes between
the xth prime P^ and P'^x+i, given the first x primes.

C. de Polignac^^^" considered the primes ^x in a progression Km-\-h.

""Comptes Rendus Paris, 116, 1893, 490; These, 1894, 45; Ann. ficole Normale, (3), 11, 1894.

""L'intermddiaire des math., 11, 1904, 149.

'■'/bMf., 20, 1913, 177.

"'/6trf., 12, 1905, 110-3.

*"Atti Ac. Sc. Torino, 47, 1911-12, 576-585.

"ojour. fur Math., 10, 1833, 201.

"'/twi., 20, 1840, 350.

"'Nouv. Ann. Math., 5, 1846, 609.

»8»Proc. Ashmolean Soc, 3, 1857, 128-131; Coll. Math. Papers, 1, 37.

""K>)mptes Rendus Paris, 54, 1862, 158-9.

Chap. XVIII] MISCELLANEOUS RESULTS ON PRIMES. 437

E. Dormoy^^^ noted that, if 2, 3, . . ., r, s, t, u are the primes in natural
order, all primes (and no others) <u^ are given by

2-3. . .stm-\-Dtat-\-tCtD,a,+tsCtC,Drar-\- . . .

-\-tsr. . .7-5C,C,Cr. . .C,D,as+ts. . .5'3C,Cs. . .C3,

where Ct is found from the quotients obtained in finding the g. c. d. of t
and 2-3 .. .rs by a rule which if applied to four quotients a, h, c, d consists in
forming in turn 1, p = cZc+l, p&-|-^, {ph+d)a+p = Ct. Further, A = ^C^=i=l,
the sign being + or — according as there is an odd or an even number of
operations in the g. c. d. process.

C. de Polignac^^^" wrote p„ for the nth prime and discussed the express-
ibility of all numbers, under a specified limit and divisible by no one of
pi, . . ., pn-i, in the form

{P2,P3,--->Pn-hPn) + {p3,P4,- ■ ■,PnPl)+. . . + (Pl, . . . , Pn-l) ,

where (a, 6, ... ) denotes ± a^b^ .... For example, every number < 53 and
divisible by neither 2 nor 3 is of the form ±3 "±2^.

J. J. Sylvester^^^ proved that if m is prime to i and not less than n, the
product (m+i)(m+2i) . . . (w+m) is divisible by some prime >n.

A. A. Markow^^*^ found a fragment in a manuscript by Tchebychef
aiding him to prove the latter's result that if // is the greatest prime divi-
sor of (1+2^) (1+4^) . . .(1+4A^^), then fx/N increases without limit with
N (cf. Hermite, Cours, ed. 4, 1891, 197).

J. Iwanow-^^ generalized the preceding theorem as follows: If fx is the
greatest prime divisor of (A + 1^). . .(A+L^), then fi/L increases without
limit with L.

C. Stormer^^^ concluded the existence of an infinitude of primes from
Tchebychef's^^^resultandusedthelattertoprovethat2'(i — l)(t — 2) . . .(i—n)
is neither real nor purely imaginary if n is any integer 5^ 3, and i = \/ — 1.

E. Landau^' (pp. 559-564) discussed the topics in the last three papers.

Braun^^" proved that the (n+l)th prime is the only root Xt^I oi

where ai = 2, 02, . . , «„ are the first n primes.

C. Isenkrahe^^^ expressed a prime in terms of the preceding primes.

R. Le Vavasseur^^° noted that all primes between p„ and p\+i, where p„
is the nth prime, are given by Sjii qiWiPJpi (mod P,J, where Pn = PiP2
• • • Pn and WiPJpi=l (mod p,).

"^Comptes Rendus Paris, 63, 1866, 178-181.

284<»Comptes Rendus Paris, 104, 1887, 1688-90.

285Messenger Math., 21, 1891-2, 1-19, 192. Math. Quest. Educ. Times, 56, 1892, 25.

286Bull. Acad. Sc. St. Petersbourg, 3, 1895, 55-8.

^^Ubid., 361-6.

"sArchiv Math, og Natur., Kristiania, 24, 1901-2, No. 5.

289Math. Annalen, 53, 1900, 42.

290M6m. Ac. Sc. Toulouse, (10), 3, 1903, 36-8.

438 History of the Theory of Numbers. [Chap, xviii

0. !Meissner^^^ stated that, if n+1 successive integers m,. . ., m+n are
given, we can not in general find another set mi,. . ., mi-\-n containing a
prime 7ni-\-v corresponding to every prime m+v of the first set. But
for n = 2, it is supposed true that there exist an infinitude of prime pairs.

G. H. Hardy ^^^ noted that the largest prime dividing a positive integer x is

m

lim lim Hm i:[l-{cos{{v\yir/x]n

r=oo TO=oo n = oo v=0

C. F. Gauss,^^^ in a manuscript of 1796, stated empirically that the
number T2ix) of integers ^x which are products of two distinct primes, is
approximately x log log x/log x.

E. Landau^^^ proved this result and the generalization

7r,(x) =

1 a^qoglogx)"-^ ''-^i-- 1 ^"-2'

{v — l)\ log a;

^ ^ |x(log log x)" ^\
1 log X J

where irXx) is the number of integers ^ x which are products of v distinct
primes; also related formulas for ir^x).

Several writers-^^ gave numerous examples of a sum of consecutive primes
equal to an exact power.

E. Landau^^^ proved that the probability that a number of n digits be a
prime, when n increases indefinitely, is asymptotically equal to l/(n log 10).

J. Barinaga^^^ expressed the sum of the first n primes as a product of
distinct primes for n = 3, 7, 9, 11, 12, 16, 22, 27, 28, and asked if there is a
general law.

Coblyn^^^ noted as to prime pairs that, when 4(6p — 2)! is divided by
36p2 — 1, the remainder is —6p — S if 6p — 1 and 6p-i-l are both primes,
zero if both are composite, — 2(6p+l) if only Qp — 1 is prime, and Qp — 1 if
only 6p4-l is prime.

J. Hammond^^^ gave formulas connecting the number of odd primes
<2n, and the number of partitions of 2n into two distinct prunes or into
two relatively prime composite numbers.

V. Brun^^*^ proved that, however great a is, there exist a successive com-
posite numbers of the form l-\-u^. There exist a successive primes no two
of which differ by 2. He determined a superior limit for the number of
primes < x of a given class.

"•Archiv Math. Phys., 9, 1905, 97.

'^^MessenRer Math., 35, 1906, 145.

"Cf. F. Klein, Nachrichten Ge.sell. Wiss. Gottingen, 1911, 26-32.

'^Ibid., 361-381; Handbuch. . .der Primzahlen, I, 1909, 205-211; Bull. Soc. Math. France, 28,

1900, 25-38.
""L'interm^diaire des math., 18, 1911, 85-6.
^*^Ibid., 20, 1913, 180.

"'L'intermddiaire des math., 20, 1913, 218.
"«Soc. Math, de France, C. R. des Stances, 1913, 55.

»»Proo. London Math. Soc, (2), 15, 1916-7, Records of Meetings, Feb. 1916, xxvii.
"""Nyt Tidsskrift for Matematik, B, 27, 1916, 45-58.

Chap. XVIII] ASYMPTOTIC DiSTKIBUTION OF PRIMES. 439

Diatomic Series.

A. de Polignac^°^ crossed out the multiples of 2 and 3 from the series of
natural numbers and obtained the "table 02":

(0) 1 (2) (3) (4) 5 (6) 7 (8) (9) (10) 11....

The numbers of terms in the successive sets of consecutive deleted numbers
are 1,3,1,3,1,..., which form the "diatomic series of 3." Similarly, after
deleting the multiples of the first n primes, we get a table a„ and the dia-
tomic series of the nth prime P„. That series is periodic and the terms after
1 of the period are symmetrically distributed (two terms equidistant from
the ends are equal), while the middle term is 3. Let 7r„ denote the product
of the primes 2, 3, . . . , P^- Then the number of terms in the period is
0(7r„). The sum of the terms in the period is x„— 0(7r„) and hence is the
number of integers <7r„ which are divisible by one or more primes ^Pn-
As applications he stated that there exists a prime between P„ and P^, also
between o" and a""^\ He^°^ stated that the middle terms other than 3 of a
diatomic series tend as n increases to become 1, 3, 7, 15, . . . , 2"* — 1, . . . .

J. Deschamps^°^ noted that, after suppressing from the series of natural
numbers the multiples of the successive primes 2, 3, . . . , p, the numbers left
form a periodic series of period 2-3 . . . p ; and similar theorems. Like
remarks had been made previously by H. J. S. Smith.^°^

Asymptotic Distribution of Primes.

P. L. Tchebychef's^^^ investigation shows that for x sufficiently large
the number 7r(a;) of primes ^a; is between 0-921Q and 1-106Q, where
Q = a:/log X. He^^^ proved that the limit, if existent, of 7r(x)/Q for x= 00 is
unity. J. J. Sylvester^^^ obtained by the same methods the limits 0-95Q
and 1-05Q.

By use of the function f (s) =2"zfn~* of Riemann, J. Hadamard^^^
and Ch. de la Vallee-Poussin^^^ independently proved that the sum of the
natural logarithms of all primes ^x equals x asymptotically. Hence
follows the fundamental theorem that -wix) is asymptotic to Q, i. e.,

. log a:
lim t:{x) — ^— =1.

'°*Recherches nouvelles sur les nombres premiers, Paris, 1851, 28 pp. Abstract in Comptes
Rendus Paris, 29, 1849, 397-401, 738-9; same in Nouv. Ann. Math., 8, 1849, 423-9.
Jour, de Math., 19, 1854, 305-333.

»«Nouv. Ann. Math., 10, 1851, 308-12.

8"Bull. Soc. Philomathique de Paris, (9), 9, 1907, 102-112

3»«Proc. Ashmolean Soc, 3, 1857, 128-131; Coll. Math. Papers, 1, 36.

3"M6m. Ac. Sc. St. P^tersbourg, 6, 1851, 146; Jour, de Math., 17, 1852, 348; Oeuvres, 1, 34.

"6BuU. Soc. Math, de France, 24, 1896, 199-220.

"«Annales de la Soc. Sc. de Bruxelles, 20, II, 1896, 183-256.

440 History of the Theory of Numbers. [Chap. XVIII

Now Q is asjinptotic to the "integral logarithm of x":

4=0 V/0 log U Jl+i log u/

so that the latter is asymptotic to irix). De la Vall^e-Poussin^^' proved that
Lix represents t{x) more exactly than x/log x and its remaining approxi-
mations . , ^ ,

x , a: , .{m — l)]x

log X log^x log'"a:

The historj^ of this extensive subject is adequately presented in the
luminous and exhaustive text by E. Landau,"*^ in which is given (pp. 908-
961) a complete list of references. The reader may consult the article by
J. Hadamard,'^^ the extensive report by G. Torelli,^^^ the summaries by
Landau,^^° also G. H. Hardy and J. E. Littlewood,^^^ and the recent papers
42-44 of Chapter XIX.

"'M^m. Couronn^s Acad. Roy. Belgique, 59, 1889, 1-74.

"^Encyclopedic des sc. math., tome I, vol. 3, pp. 310-345.

"Utti R. Accad. Sc. Fis. Mat., XapoU, (2), 11, 1902, No. 1, 222 pp.

^oProc. Fifth Internat. Congress, Cambridge, 1, 1913, 93-108. Math. Zeitschrift, 1, 1918, 1-24,

213-9.
«»Acta Math., 41, 1917, 119-196.

*

I

i

CHAPTER XIX.

INVERSION OF FUNCTIONS; MOBIUS' FUNCTION fi(n); NUMERICAL
INTEGRALS AND DERIVATIVES.

Inversion; Function fx{n).

A. F. Mobius^ defined the function /.i(n) to be zero if n is divisible by a
square >1, but to be ( — 1)'^ if n is a product of k distinct primes >1,
while ^i(l) = 1. He employed the function in the reversion of series:

Fix) = S '-^ imphes fix) = S fxis) -^'

s=l " s=l "

His results were expressed in more general form by Glaisher^^ and cited in
Chapter X. See also E. Meissel,^ who^ noted that

R. Dedekind"* proved that, if F{m) =2/(d), where d ranges over all the
divisors of m, then

+ .

(2) /w=.w-z.o+..e)-..(^)

where the summations extend over all the combinations 1, 2, 3, ... at a time
of the distinct prime factors a, b,. . ., k oi m. The proof follows from a
distribution of all the factors of m into two sets S and T. Put all the divisors
of m into set S] all divisors of m/a into set T, all of m/b into T, etc. ; all divi-
sors of m/iab) into S, all of m/iac) into S, etc.; all of m/{abc) into T, etc.
Then, with the exception of m itself, every divisor of m occurs as often in the
set S as in the set T. In particular, for Euler's 0(m), m= 20(d), whence

For another example, see Dedekind''^ of Ch. VIII. Similarly, F(w) =
n/(d) implies

F(m) UF g) . . .

/(») =

H^Mi-:)-

J. Liouville^ stated simultaneously with Dedekind the inversion theorem
for sums and made the same appHcation to ({)im).

Liouville^ stated the theorem for sums as a problem.

iJour. fiir Math., 9, 1832, 105; Werke, 4, 591. He wrote a„ for /x(n).

Hbid., 48, 1854, 301-316.

'Observationes quaedam in theoria numerorum, Berlin, 1850, pp. 3-6.

*Jour. fiir Math., 54, 1857, pp. 21, 25.

6Jour. de Math^matiques, (2), 2, 1857, 110-2.

«Nouv. Ann. Math., 16, 1857, 181-2.

441

442 History of the Theory of Numbers. [Chap. XIX

B. Merry' gave a proof by noting that, if d is any divisor of m, and if q
of the prime factors of m occur to the same power in c? as in ???, then f{d)
occurs once in F{m), q times in ZF{m/a), q{q — l)/2 times in 'LFim/ab), etc.
Thus the coefficient of f{d) in (2) is

if 5 > 0, but is unity ii q = 0,i. e.,ii d = m. This proof is only another way of
stating Dedekind's proof. I

R. Dedekind^ gave another form and proof of his theorems. Let

(-i)(-i)

m(l--)(l-T 1 . . =2j/i-2j/2,

where vi ranges over the positive terms of the expanded product and —V2
over the negative terms. A simple proof shows that, if v is any di\'isor
<m of m, there are as many terms vi di\'isible by v as terms V2 divisible by v.
Thus

i:f{v)=F{m), Uf{p)=F{m)

imply, respectively,

fim) =2F(.,) -2F(^2), Km) -^^y

Liou\'ille^ wTote F(n) =Tif{n/D''), where D ranges over those di\4sors of
n = a"}/ ... for which D" divides n. Then

f{n) =F{n) -XFin/a") +lF{n/a''b'') -....

E. Laguerre^ expressed (2) in the form

(3) /(m)=2M(|)F(d),

where d ranges over the divisors of m. Let

2/(n)T^=SF(n)x^

n = l L—X n=l

whence F{m) ='Zf(d). For m^Up", where the p's are distinct primes, let
f{m) =n/(p»), and/(p") =p''-np-l). Then

F{m) =njl+/(p) + . . . +f{p''-')] =Up'' = m.

The hypotheses are satisfied if / is Euler's function 4>. This discussion
deduces l,(t){d)=m from the usual expression of type (3) for <j){m), rather
than the reverse as claimed.
N. V. Bougaief^° proved (1).

F. Mertens" defined /x(n) and noted that 2/x(d)=0 if n>l, where d
ranges over the divisors of n.

'Nouv. Ann. Math. 16, 1857, 434.

8Dirichlet's Zahlentheorie, mit Zusatzen von Dedekind, 1863, §138; ed. 2, 1871, p. 356; ed. 4,

1894, p. 360.
'"Jour, de Math., (2), 8, 1863, 349.
•BuU. Soc. Math. France, 1, 1872-3, 77-81.

'"Mat. Sbomik (Math. Soc. Moscow), 6, 1872-3, 179. Cf. Sterneck."
"Jour, fur Math., 77, 1874, 289; 78, 1874, 53.

I

Chap. XIX]

Inversion; Function fj>{n).

443

E. Cesaro^^ proved formulas, quoted in Ch. X, which include (3) as a
special case. His erroneous evaluation of the mean of /x(n) is cited there.

Cesaro^^ reproduced the general formula just cited and extended it to
three pairs of functions:

S/i(d)i^i(^) =l^f2(d)F,(^ =S/3(rf)/^3(^),

FM =S/2(rf)/3 (^) , F, =2/3/1, Fs =2/^2.

where, in each, d ranges over the divisors of n.
Cesaro^^ noted that, if h(ri)-\-k{n) = 1 and

H{n)=h{p)Hq)..., Kin)=k(p)kiq)...,

where p, q,. . . are the prime factors of n, then

Hin) =i:fjiid)K{d), Kin) =Xfx{d)H{d).

For h{n)=k{n) = 1/2, then H{n)=K{n) is the reciprocal of the number of
divisors, without square factors, of n.

Cesaro^^ treated the inversion of series. Let Q{x) = 1 or 0, according as x
is or is not in a given set Q, of integers. Let Q{x)Q,{y) =U(xy). Let €i{x) be
functions such that €„{e^(x)} =€„^(x) for every pair of indices a, j8. Then

F{x)=Xh{o,)fleM],
where co ranges over all the numbers of Q,, implies that

fix)=i:H{c^)F{eM},

if the sum Xh{d)H{n/d), for d ranging over the divisors of n, equals 1 or 0
according as n = 1 orn> 1. Cf . Mobius\

N. V. Bougaief^^ considered the function v{x) with the value log p if x
is a power of a prime p, the value 0 in all other cases. Then, if d ranges
over the divisors of n, St'(d) =log n implies 2ju(d) log d= —v{n).

H. F. Baker^'^ gave a generalization of the inversion formula, the state-
ment of which will be clearer after the consideration of one of his appli-
cations of it. Let fli,. . ., a„ be distinct primes and S any set of positive
integers. For k-^n, let F{ai,. . ., a^) denote the set of all the numbers
in S which are divisible by each of the primes a^t+i, o,k+2,- • ■, cin, so that
F(ai, . . . , aj =*S. For A; = 0, write F{0) for F, so that i^(0) consists of the
numbers of S which are divisible by ai,. . ., a„. Returning to the general
F{ai,. . ., ttk), we divide it into sub-sets. Those of its numbers which are
divisible by no one of ai, . . ., a^ form the sub-set /(ai, . . ., %)• Those
divisible by ai, but by no one of 02, ... , ak, form the sub-set /(a2, Os, ■ • • , dk)-

i^Mem. soc. roy. sc. de Liege, (2), 10, 1883, No. 6, pp. 26, 47, 56-8.

I'Giornale di Mat., 23, 1885, 168 (175).

"/bid., 25, 1887, 14-19. Cf. 1-13 for a type of inversion formulas.

"AnnaU di Mat., (2), 13, 1885, 339; 14, 1886-7, 141-158.

isComptes Rendus Paris, 106, 1888, 652-3. Cf. Cesaro, ihid., 1340-3; Cesa,ro,i2 pp. 315-320;
Bougaief, Mat. Sbornik (Math. Soc. Moscow), 13, 1886-8, 757-77; 14, 1888-90, 1-44,
169-201; 18, 1896, 1-54; Kronecker3« (p. 276); Berger"'' (pp. 106-115); Gegenbauer^^ of
Ch. XI— all on -Ln^d) log d.

"Proc. London Math. Soc, 21, 1889-90, 30-32.

444 History of the Theory of Numbers. [Chap, xix

Those di\'isible by Oi and 02, but by no one of 03, ... , a^, form the sub-set
/(oa,. . ., a J. Finally, those divisible by fli. . ., O;. form the sub-set desig-
nated /(O). Thus

F{ai,a-2, . . ., Ok) =/(ai, Oo, . . . , a^) +2/(a2, as, •• • , Oa) +|/(a3, ^4, • • • , a^t)

+ ...-f2/(a,)H-/(0),

7»— 1

where S indicates that the summation extends over all combinations of
Oi,. . . , flr taken* /c — r at a time.

WTien we have any such set or function /(oi, . . . , a^t), uniquely determined
by Oi, . . . , Qk, independently of their order, and we define F by the foregoing
formula, then we have the inverse formula
/(oi, 02, . . . , a„) =F(ai, 03, ... , aj -2/^(a2, 03, ... , aj +2/^(03, 04, . . . ,aj

-...+(-ir-^SF(aO + (-irF(0), '

n-l

where S now indicates that the summation extends over all the combina-

r

tions of fli,. . ., a„ taken n — r at a time. The proof is just like that by
B. Merry for Dedekind's formula.

To give an example, let n = 2, ai = 2, 02 = 3, S = S, 4, 6, 8. Then F{ai)

= 3, 6;/(oi)=3, /(0)=6; F(a2)=4, 6, 8; /(o2)=4, 8. Thus

F(oi,O2)-/^(o0-F(o2)+F(0)=5-(3,6)-(4,6,8)+6=0=/(oi,O2).

A. Berger^^'' called /i conjugate to /a if 2/i id)f2{d) = 1 f or ^• = 1 , 0 f or A:> 1 ,
when d ranges over the divisors of k. Let g{mn)=g{m)g{n), ^(1) = 1.
Write h{k)=Zf{d)Md)g{8), where d8 = k. Then fik)=2f.2{d)g{d)h(8).
Dedekind's inversion formula is a special case. For, if /i(n) = l, then
/2(n)=M(w).

K. Zsigmondy^^ stated that if, for every positive integer r,

?f{r;)=F{r),

where c ranges over all combinations of powers ^r of the relatively prime
positive integers ni, . . ., n^, while r,. denotes the greatest integer ^r/c, then

/(r)=F(r)-2F(r„)+SF(r„„0-...,

n n,n

where the summation indices n, n' ,. . . range over the combinations of
ni, . . . , rip taken 1,2,... at a time.

R. D. von Sterneck^^ noted that, if d ranges over the divisors of n
l^B{d) =^{n) implies that

Taking m=l,. . ., n and solving, we get Q{n) expressed as a determinant
of order n, whence

^(n)=,A(^)-S,A(di)+2:V'W----+(-l)VR),
if n = pi°'. . .p/" and d^ is derived from n by reducing p exponents by unity.

*Here and in the statement of the theorem occur confusing misprints for k and n.
""Nova Acta Regiae Soc. Sc. Upsaliensis, (3), 14, 1891, No. 2, 46, 104.
"Jour, fur Math., Ill, 1893, 346. Apphed in Ch. V, Zsigmondy."
"Monatshefte Math. Phys., 4, 1893, 53-6.

Chap. XIX]

Inversion; Function fx{n).

445

P. Bachmann^° proved that f{n) ='Zlz^F{kn) implies that

F(l)

S ii{n)f{n).

n=l

Write X = [x/n\. Taking F{n) =X, nX, <J>(Z), whence /(n) = T{X), no-(X),
D{X), respectively, we obtain Lipschitz's^° (Ch. X) formulas:

ti

[x]= 2 iJi{n)T\-\=2fji{n)na

n

*[a:]=2/x(??)i)

[Q

Let F{n) be zero if n is not a divisor of P and write x{/{P/n) for /^(n).
Hence if d divides P, f{d)=7:4^{P/kd) implies iA(P) =Sm(^)/(^), where
A; ranges over the divisors of P/d, and d over those of P.

D. von Sterneck^^ considered a function f(n) with the properties:
(i) /(I) = 1 ; (ii) the g. c. d. of /(m) and/(n) isf{d) if rf is the g. c. d. of m and n;
(iii) for primes p, other than specified ones, one of the numbers /(p±l) is
divisible by p; (iv) the g. c. d. oi f{pn)/f{n) and /(n) divides p. Then if
L{n) is the 1. c. m. of the values of / for all the divisors <n of n, F{n) =f{n)
■i-L{n) is an integer which can be given the form

Fin) =

^\PrpJ ^\p,PiPkVl)'

W \pmpk}'"

n=Jlpi

The four properties hold for the function defined by the recursion
formula /(n) =a/(n — l)+i3/(n — 2), where a and jS are relatively prime,
with the initial conditions /(I) = 1 , /(2) = a. For a = 2x,p = b — x^, we have^^

(x+Vbr-ix-VbT

m=

2\/b

The case a = j3 = l was discussed by Lucas-^ of Ch. XVII, and his test for
primality holds for the present generalization.
The four properties hold also for

Kn) =

aJ'-lf

if a, h are relatively prime ;^^ then fip — l) is divisible by p if p is a prime
not dividing a, b or a — b.

K. Zsigmondy-^ gave a generalized inversion formula. Let A^ be any
multiple of the relatively prime integers ni, . . . , n^. Set

where d ranges over those divisors ^m oi N which are products of powers

2"Die Analytische Zahlentheorie, 1894, 310.
"Monatshefte Math. Phys., 7, 1896, 37, 342.
22DirichIet, Werke, 1, 47-62. See Dirichlet,^ Ch. XVII.
wZsigmondy, Monatshefte Math. Phys., 3, 1892, 265.
^Ibid., 7, 1896, 190-3.

446 History of the Theory of Numbers. [Chap, xix

of rii, . . . , 7J,. Then, if a ranges over those divisors d which are divisible by
no one of ^i, . . . , v^', chosen from nj, . . . , n^,

The left member equals F{m, N, e) constructed for the numbers other
than Vi,..., V,' of the set ni, . . . , /z^. For s' = s, we have

I

f(m, N, e) =F(m, N, e) -Si^([f ]' ^' ^n^

+ .

The latter becomes the series in Bachmann^° when m=cD, N = 0, € = 1,
while rii, n2, . . . are primes.

F. Mertens^^ considered (7(n) =ju(l)H-/i(2) + . . . +M(n) and proved that

l.o)[f]=.g)+.(l)+.. .+.©-..(.).

<rin) = 2a{g) - X n{rMs) f^l , g = [V^].

r. s=i LrsJ

By means of a table (pp. 781-830) of the values of a{n) and /x(n) forn< 10000,
it is verified that \(7{n)\< \/n for 1< n< 10000.

D. von Sterneck^^ verified the last result up to 500 000, and for 16 larger
values under 5 million.

A. Berger" noted that, if g{m)g{n)=g{mn), ^(1) = 1,
i:n{d)gid)=U{l-gip)] (n>l),

where d ranges over all divisors of n, p over the prime divisors of n. If
Xg{m) is absolutely convergent,

sM%W=n{i-^(p)),

where p ranges over all primes.

D. von Sterneck^^ noted that, if 6ix) ^ 1 for every x and if

|j.w|<^6-H|/(.)-/[g-/[=]-/[g|.

In particular, |2iu(/c)|<8+?z/9.

D. F. Seliwanov'-^ gave Dedekind's formula with appHcation to <t>{n).
H. von Koch^^" defined n{k) by use of infinite determinants.

"Sitzungsber. Ak. Wiss. Wien (Math.), 106, II a, 1897, 761-830.

»Ibid., 835-1024; 110, Ila, 1901, 1053-1102; 121, Ila, 1912, 1083-96; Proc. Fifth Intern. Con-
gress Math., 1912, I, 341-3.
"Ofversigt Vctenskap.s-Akad. Forhand., Stockholm, 55, 1898, 579-618.
"Monatshcfte Math. Phys., 9, 1898, 43-5.
"Math. Soc. St. Paersbourg, 1899, 120.
""Ofversigt K. Vetensk.-Akad. Forhand., Stockholm, 57, 1900, 659-68.

Chap. XIX] INVERSION) FUNCTION fx{n). 447

E. B. EUiott^^ of Ch. V gave a generalization of fx{n).

L. Kronecker^" defined the function p{n, k) of the g. c. d. (n, k) of n, k
to be 1 if (n, A:) = 1, 0 if (n, A;)>1, and proved for any function /(n, k) of
(n, k) the identity

S p{n, k)f{n, k) =X S [x{d)fin, kd),

k=l d k=\

where d ranges over the divisors of n. The left member is thus the sum of
the values oif{n, k) ior k<n and prime to n. Set

Fin, rf) = S f(n, kd) , $(n, d) = "s p (^, k)fin, kd) .

k=i k=i \tt /

Thus when d ranges over the divisors of n,

Fin, 1) =S$(n, d), *(n, 1) =2M(d)F(n, d)

d

are consequences of each other. The same is true (p. 274) for
/i(n)=S/(d)^(^), fin) =i:ixid)gid)h{^,

if girs) =gir)gis). Application is made (p. 335) to mean values.

E. M. L^meray^^ gave a generalized inversion theorem. Let i/'2(a, b) be
symmetrical in a, b and such that the function ^3 defined by

\f/sia, b, c)=\l/2{a,-ip2ib, c)\

is symmetrical in a, b, c. Then the function

\pM, b, c, d) =\l/3[a, b, yPiic, d)}

will be symmetrical in a, b, c, d and similarly for t^fc(ai, . . . , 0;^) . For example,

\l/2ia, b)=aVl-\-b^+bVT+c^, ^3 = a&c+SaVl+6Vl+c2.

Let v=^iy, u) be the solution of y=yp2i'^j ^) for ^- The theorem states that,
li di,. . .,dk are the divisors of m = p°gV. . , and if Fim) be defined by

Fim)=Mfid,),...Jidj:)],

we have inversely /(m) =Q(G, H), where

G=4.w,.£),.g),... ,.(-!-),...},

^=4K?)-(f)'-<^)'-;}

where ix is the number of combinations of the distinct prime factors p,
q,... of m taken 0, 2, 4, ... at a time, and v the number taken 1, 3, 5, ... at a
time.

L. Gegenbauer^^ defined ^lix) to be +1 if a: is a unit of the field Rii) of
complex integers or a product of an even number of distinct primes of

soVorlesungen iiber Zahlentheorie, I, 1901, 246-257. His €„ is /i(n).
31N0UV. Ann. Math., (4), 1, 1901, 163-7.

32Verslag. Wiss. Ak. Wetenschappen, Amsterdam, 10, 1901-2, 195-207 (German.) English
transl. in Proc. Sect. Sc. Ak. Wet., 4, 1902, 169-181.

448 History of the Theory of Numbers. [Chap, xix

R{i), — 1 if a product of an odd number, 0 if x is di\'isible by the square of a
prime of R{i). Let [771] denote a complete set of residues ?^0 of complex
integers modulo m. Then the sum of the values of fix) for all complex
integers x relatively prime to a given one n, which are in [m], equals
2jLi(c?)2/(d'x), where d ranges over all divisors of n in [m], and x ranges
over {rn/d}. This is due, for the case of real numbers, to Nazimov^" of
Chapter V. Again, 2/i((i) = l or 0 according as norm n is 1 or >1. Also
2/(d) =F(7?) miplies Xfi{d)F(n/d) =f{n).

J. C. Kluyver^ employed Kronecker's^" identity for special functions /
and obtained known results like

2 cos — =/x(n), n 2sin — = e^^''\

n n

where v ranges over the integers <Ji and prime to n, while y{n) is Bouga-
ief's^^ function p{n).

P. Fatou^ noted that Merten's a{n) does not oscillate between finite
limits. E. Landau^^ proved that it is at most of the order of ne', where
t = — aVlog n. Landau^® noted that Furlan" made a false use of analysis
and ideal theory to obtain a result of Landau's on Merten's^^ (r(n).

0. ■Meissner^^" emploj-ed primes p,, q,. For n=Up'i set Z(n)=nei''>
and Z2{n) = Z\Z{n)\. Then Z{?i) = n only if n is Up.^i or 16 or Hjp'iqii.
Next, Z2(n)=n in these three cases and when the exponents e, in n are
distinct primes; otherwise, Z2(n)<n. We have [1/Z{n)]=fx'^{n).

R. HackeP^ extended the method of von Sterneck^^ and obtained vari-
ous closer approximations, one^^ being

xe{k)

<^+io2+|2/g]-2/[g|,

26

where a = l, 6, 10, 14, 105; 6 = 2, 3, 5, 7, 11, 13, 385, 1001.
W. Kusnetzov-^^ gave an analytic expression for ;u(n).
K. Knopp^^° of Ch. X gave many formulas involving n{n).
A. Fleck''"" generahzed n{m)=iJLi{m) by setting

M*(m)=n(-l)»'(f), m=Upr.

,=1 \a,/ ,=1

Using the zeta function (12) of Ch. X, and ^^ of Fleck^-^ of Ch. V, we have

y r^\ r \ V ^k-\{m) . . * ^t(m) ^ (m\

i:Hk{d)=fXk-i{m), S — — — =f(s) 2 — — -, <t)k{m) = Xdfik+A-T)-

dim fn = l ^ m = l ^ dm \"/

"Verslag. Wiss. Ak. Wetenschappen, Amsterdam, 15, 1906, 423-9. Proc. Sect. Sc. Ak. Wet.,

9, 1906, 408-14. "Acta Math., 30, 1906, 392.

«Rend. Circ. Mat. Palermo, 26, 1908, 250. "Rend. Circ. Mat. Palermo, 23, 1907, 367-373-

"Monatshefte Math. Phys., 18, 1907, 235-240.
»"Math. Xaturw. Blatter, 4, 1907, 85-6.
"SitzunKsber. Ak. Wiss. Wien (Math.), 118, 1909, II a, 1019-34.
'•Sylvester, Messenger Math., (2), 21, 1891-2, 113-120.
«°Mat. Sbomik (Math. Soc. Moscow), 27, 1910, 335-9.
'■wSitzungsber. Berlin Math. GeseU., 15, 1915, 3-8.

Chap. XIX] NUMERICAL INTEGRALS AND DERIVATIVES. 449

The theorem Sn=iM(^)A = 0 and other results on sums involving /i(n)
play an important role in the theory of the asymptotic distribution of
primes. In accord with the plan of not entering into details on that topic
(Ch. XVIII), the reader is referred for the former topic to the history and
exposition by E. Landau,^^ and to the subsequent papers by A. Axer,^^
E. Landau/3 and J. F. Steffensen.^''

Proofs of (2) or (3) are given in the following texts :

P. Bachmann, Die Lehre von der Kreistheilung, 1872, 8-11; Die Elemente der
Zahlentheorie, 1892, 40-4; Grundlehren der Neueren Zahlentheorie, 1907, 26-9.
T. J. Stieltjes, Theorie des nombres, Ann. fac. Toulouse, 4, 1890, 21.
Borel and Drach, Introd. theorie des nombres, 1895, 24-6.
E. Cahen, ;Sl6ments de la theorie des nombres, 1900, 346-350.
E. Landau," 577-9.

Numerical Integrals and Derivatives.

N. V. Bougaief^^ (Bugaiev) called F{n) the numerical integral of /(n) if
F(m) =2/(5), summed for all the divisors 5 of m, and called /(n) the numer-
ical derivative function of F{n), denoted by DF(n) symbolically.

Granting that there is, for every n, the development

F{n) = a,[n]+a2y^j '^^Hjj

+

where [x] is the largest integer ^x, then a^ is the numerical derivative of
F{k) -F{k-1). He developed [n'^% [n'% etc.

N. V. Bougaief,^^ after amplifying the preceding remarks, proved that

S e{8)x{d) =yp{n), d(n)d(m) =d{nm)

d6=n

imply

Writing D~^d{d) for '29(d), summed for the divisors d^ of n, we have

D'^2x{md)=^2xi^)D''d{d),
for any integer /x, positive or negative. There are formulas like

"Handbuch. . .Verteilung der Primzahlen, II, 1909, 567-637, 676-96, 901-2.

«Prace mat. fiz., Warsaw, 21, 1910, 65-95; Sitzungsber. Ak. Wiss. Wien (Math.), 120, 1911,

II a, 1253-98.
«Sitzungsber. Ak. Wiss. Wien. (Math.), 120, 1911, Ila, 973-88; Rend. Circ. Mat. Palermo, 34,

1912, 121-31.
"Analytiske Studier. . ., Diss., Kjobenhavn, 1912, 148 pp. Fortschritte, 43, 262-3. Extract

in Acta Math., 37, 1914, 75-112.
*^ Journal de la Soc. Philomatique de Moscou, 5, 1871.
**Theory of numerical derivatives, Moscow, 1870-3, 222 pp. Extracts from Mat. Sbomik

(Math. Soc. Moscow), 5, I, 1870-2, 1-63; 6, 1872-3, I, 133-180, 199-254, 309-360

(reviewed in BuU. Sc. Math. Astr., 3, 1872, 200-2; 5, 1873, 296-8; 6, 1874, 314-6).

R^8um6 by Bougaief, BuU. Sc. Math. Astr., 10, I, 1876, 13-32.

450 History of the Theory of Numbers. [Chap, xix

u = l u = l L"J

ld(^fj^e(x^ (mod 2), 20^^) -2d(£j^d{^n) (mod 3),

where 6{n) is the number of primes a^n. Other special results were cited
under 155, Ch. V; 6, Ch. XI; 217, Ch. XVIIL

E. Ces^ro^^" treated 2/(5) in connection with median and asymptotic
formulas.

Bougaief^^ treated numerical integrals, noting formulas like

liP'"'

where ^(n) is the number of prime factors a, b,. . . of n = a°6^ . . . ,
2 rPid) = 2 \l/(d)+ 2 rPia'd) = 2 yp{ad)+ 2 yp{d).

'^i" d\i dr d\i dL^

Bougaief^^ gave a large number of formulas of the type

2V^(d)[^] =2V(rf)+2"*/^V(^)+Sf'»/^V(rf)+ • • .,

where, on the left, d ranges over all the di\isors of m; while, on the right, d
ranges over those divisors of m which do not exceed n, [n/2], . . ., respectively.
Bougaief°^ gave the relation

Xd(Vd)=^U^2'n):
d\n P \P /

where p ranges over all primes ^ -y/n, and ^^(t??, n) is the sum of the kth.
powers of all di\'isors ^m of n, so that ^o is their number, and ^(0 is the
number of primes ^t.

L. Gegenbauer^'^ noted that the preceding result is a case of

S,(d).(JJ/(X)=J/(X){2,W.(3},

where dx ranges over the divisors ^X of n. Special cases are

Y%(<f) =yUa'. n), ^d%{(^)^^2a%{l, n),

where |p {m, n) is the sum of the pth powers of the di\'isors ^m of n.

«^Giornale di Mat., 2.5, 18S7, 1-13.

"Mat. Sbornik (Math. Soc. Moscow), 14, 1888-90, 169-197; 16, 1891, 169-197 (Russian).

"Ibid., 17, 1893-5, 720-59.

"Comptes Rendus Paris, 119, 1894, 1259.

•oMonatshefte Math. Phys., 6, 1895, 208.

Chap. XIX] NUMERICAL INTEGRALS AND DERIVATIVES. 451

Bougaief^"" noted that, for an arbitrary function \p,

<* J M=l n = l M=l n=l u = ln=l

N. V. Bervi" treated numerical integrals extended over solutions of
indeterminate equations, in particular for n = a-\-h{x-{-y)-\-cxy, h^ = b+ac.

Bougaief^" considered definite numerical integrals, viz., sums over all
divisors, between a and b, oi n. He expressed sums of [x], the greatest
integer ^x, as sums of values of f (n, m), viz., the number of divisors ^n
of m. Also sums of ^s expressed as ^i{l)+^i{2)-\- . . .-{-^i{n), where
fi(n) is the number of the divisors of n which are ith. powers.

1. 1. Cistiakov^^" (Tschistiakow) treated the second numerical derivative.

Bougaief^^^ gave 13 general formulas on numerical integrals.

Bougaief^^ gave a method of transforming a sum taken over 1, 2, . . ., n
into a sum taken over all the divisors of n. He obtains various identities
between functions.

D. J. M. Shelly, ^^ using distinct primes a,h,. . ., called

^'=K^^•••)

the derivative of iV = a^b^ .... Similar definitions are given for derivatives
of fractions and for the case of fractional exponents a, j8, . . . . The primes
are the only integers whose derivatives are unity.

ec^Comptes Rendus Paris, 120, 1895, 432-4.

«iMat. Sbornik (Math. Soc. Moscow), 18, 1896, 519; 19, 1897, 182.

^mid., 18, 1896, 1-54 (Russian); see Jahrb. Fortschritte Math., 27, 1896, p. 158.

«2o/6id., 20, 1899, 595; see Fortschritte, 1899, 194.

^^^Ibid., 549-595. Two of the formulas are given in Fortschritte, 1899, 194.

«/6id., 21, 1900, 335, 499; see Fortschritte, 31, 1900, 197.

"Asociaci6n espanola, Granada, 1911, 1-12.

CHAPTER XX.

PROPERTIES OF THE DIGITS OF NUMBERS.

John HilP noted that 139854276=118262 is formed of the nine digits
permuted and believed erroneously that it is the only such square.

N. BrownelP" found 169 and 961 as the squares whose three digits are
in reverse order and whose roots are composed of the same digits in reverse
order. The least digit in the roots is also the least in the squares, while the
greatest digit in the roots is one-third of the greatest in the squares and
one-half of the digit in the tens place.

W. Saint^'' proved that every odd number N not divisible by 5 is a divisor
of a number 11 . . .1 oi D^N digits [by a proof holding only for N prime
also to 3]. For, let 1 ... 1 (to D digits) have the quotient q and remainder
r when divided by D. This remainder r must recur if the number of digits
1 be increased sufficiently. Hence let 1...1 (to D+d digits) give the
remainder r and quotient Q when divided by D. By subtraction, D{Q — q)
= 1. . .10. . .0 (with d units followed by D zeros). Hence if 1. . .1 (to d
digits) were not divisible by every odd number ^ D and prime to 5 [and to
3], there would be a remainder R; then RO. . .0 (with D zeros) would be
divisible by an odd number prime to 5 [and to 3], which is impossible.

P. Barlow^" stated, and several gave inadequate proofs, that no square
has all its digits alike. He^'^ stated and proved that 111111111^=1 23456-
78987654321 is the largest square such that if unity be subtracted from each
of its digits and again from each digit of the remainder, etc., all zeros being
suppressed, each remainder is a square. Denote (10^ — 1)/(10 — 1) by [k].
Then |^(x+l)p has x digits and exceeds [x] by 10{|(a: — l)p. Since
zeros are suppressed we have a square as remainder, and the process can
be repeated. It is stated that therefore the property holds only for V,
IV, IIP, ....

Several^* found that 135 is the only number N composed of three digits
in arithmetical progression such that the digits will be reversed if 132 times
the middle digit be added to N.

W. Saint ^•'^ found the least integral square ending with the greatest num-
ber of equal digits. The possible final digits are 1, 4, 5, 6, 9. Any square is
of the form 4n or 4n+l. Hence the final digit is 4. If the square termi-
nated with more than three 4's, its quotient by 4 would be a square ending
with two I's, just proved to be impossible. Of the numbers ending with

^Arithmetic, both ia Theory and Practice, ed. 4, London, 1727, 322.
i«The Gentleman's Diary, or Math. Repository, London, 1767; Davis' ed., 2, 1814, 123.
ifcJour. Nat. Phil. Chem. Arts (ed., Nicholson), London, 24, 1809, 124-6.
I'^The Gentleman's Diary, or Math. Repository, London, 1810, 38-9, Quest. 952.
^^Ibid., 1810, 39-40, Quset. 953.
^^Ibid., 1811, 33-4, Quest. 960.

I/Ladies' Diary, 1810-11, Quest., 1218; Leybourn's M. Quest. L. D., 4, 1817, 139^1.

453

454 History of the Theory of Numbers. [Chap. XX

three 4's, the least is 1444. J. Davey discussed only numbers of 3 or 4
digits of which the last 2 or 3 are equal, respectively.

Several^" found that the squares 169 and 961 are composed of the same
digits in reverse order, have roots of two digits in reverse order, while
the sum of the digits in each square equals the square of the sum of the
digits in each root; finally, the sum of the digits in each root equals the
square of their difference.

An anonymous writer^ proposed the problem to find a number n given
the product of n by the number obtained from n by writing its digits in
reverse order [Laisant*^].

P. T^denat^ considered the problem to find a number of n digits whose
square ends with the same n digits in the same order. If a is such a number
of n — 1 digits, so that a^ = 10'*~^64-a, we can find a digit A to annex at the
left of a to obtain a desired number 10"~^A + a of n digits. Squaring the
latter, we obtain the condition {2a — l)A= —b (mod 10).

J. F. Frangais^ noted the solutions

x = 2"p = 5"5 + l, x2 = 10"p5+a:,

2/ = 5«r = 2"s + l, y^ = lO"rs-\-y,

in which the resulting condition 2"p — 5"^ = 1 or 5"r — 2"s= 1 is to be satisfied.
Special solutions are given by n = 1, p = 3; n = 2, p = 19; n = 3, p = 47; n = 4,
p = 586; etc., to n = 7.

J. D. Gergonne^ generalized the problem to base B. Then

x(rc-l)=5"t/.

Let p, q be relatively prime and set jB" = pq. Then x = pt, x — l=qu, or vice
versa. The condition pt — qu = l is solved for t, u. When B = 10, n = 20,
the least u is 81199.

Anonymous writers^ stated and proved by use of the decimal fraction for
1/n that every number divides a number of the form 9 ... 90 ... 0.

A. L. Crelle^ proved the generalization : Every number divides a number
obtained by repeating any given set of digits and affixing a certain number of
zeros, as 23.. .230.. .0.

Several^" found a square whose root has two digits, their quotient be-
ing equal to their difference. By x/y=x—y, x=i/+l + l/(2/ — 1), an inte-
ger, whence y=2, x=4t. Thus the squares are 24^ or 42^.

The^^ three digits of a number are in geometrical progression; the prod-
uct of the sum of their cubes by the cube of their sum is 1663129; if the
number obtained by reversing the digit be divided by the middle digit, the

^ffLadies' Diary, 1811-12, Quest. 12.31; Leybourn, I. c, 153-4.

»Annales de Math, (ed., Gergonne), 3, 1812-3, 384.

*Ibid., 5, 1814-5, 309-321. Problem proposed on p. 220.

*Ibid., 321-2.

^Ibid., 322-7.

*Ibid., 19, 1828-9, 256; 20, 1829-30, 304-5.

Ubid., 20, 1829-30, 349-3.52; Jour, fiir Math., 5, 1830, 296.

^"Ladies' Diary, 1820, 36, Quest. 1347.

'I'Ibid., 1822, 33, Quest. 1374.

i

Chap. XX] PROPERTIES OF THE DiGITS OF NXJMBERS. 455

quotient is 46|. By the last condition, the middle digit must be 3, since
not a higher multiple of 3. Hence the number is 931.

To find a synunetrical number abcba of five digits whose square exhibits
all ten digits, W. Rutherford^" noted that the square is divisible by 9 since
the sum of the digits is divisible by 9. Hence the sum of the digits of the
number is divisible by 3. Also a ^ 3. Taking c = a-{-b, c=S,he got 35853.
J. Sampson noted also the answers 84648, 97779,

J. A. Grunert^ proved by use of Euler's generahzation of Fermat's the-
orem that^ every number divides 9 . . . 90 . . .0. ---^

Drot^" asked for the values of x for which N"" has the same final k digits
as N, when ^ = 1, 2 or 3.

J. Bertrand^'' discussed the numbers of digits of certain numbers.

A. G. Emsmann^ treated a number 6 of n digits to base 10 equal to the
product of the sum of its digits by a, and such that if another number of n
digits be subtracted from b the remainder shall equal the number obtained
by writing the digits of b in reverse order.

J. Booth^° noted that a number of six digits formed by repeating any set
of three digits is divisible by 7, 11, 13 [since by 1001].

. G. Bianchi^^" noted various numerical relations like 10^ = 11111111 +
8.1111111 + 8.9.111111+... + 8.9M + 9^ = 2222222 + ...+7.8^2+8^ 98 =
(12-1-0)9-1, 987 = (123-12-l)9-3, 9876 = (1234-123-13)9-6.

C. M. Ingleby^^ added the digits of a number N written to base r, then
added the digits of this sum, etc., finally obtaining a number, designated
SN, of a single digit; and proved that S{MN)=S{SM-SN).

P. W. Flood^^" proved that 64 is the only square the sum of whose digits
less unity and product plus unity are squares.

G. Cantor^^ employed any distinct positive integers a, 6, ... , considered
the system of integers in which a occurs a times, b occurs b times, etc., and
called a system simple if every number can be expressed in a single way in the
form aa+/36+ . . ., where a = 0, 1,. . ., a; /3 = 0, 1, . . ., 6; . . .. A system is
simple if and only if each basal number k divides the next one I and if k
occurs k = (l/k) — 1 times.

G. Barillari^^ noted that, if 10 belongs to the exponent m modulo b,
the number P = a/3 . . . Xa/3 ... X ... , obtained by repeating h times (/i > 1) any
set of n digits, is divisible by 6 if 6 is prime to 10^-1 and if nh is a multiple

'^Ladies' Diary, 1835, 38, Quest. 1576.

8Jour. fur Math., 5, 1830, 185-6.

^'^Nouv. Ann. Math., 4 1845, 637-44; 5, 1846, 25. For references to tables of powers, 13,

1854, 424-5.
oblbid., 8, 1849, 354.

"Abhandlung liber eine Aufgabe aus der Zahlentheorie, Progr. Frankfurt, 1850, 36 pp.
loProc. Roy. Soc. London, 7, 1854-5, 42-3.
^""Proprieta e rapporti de' numeri interi e composti coUe cifre semplici . . . , Modena, 1856.

Same in Mem. di Mat. e di Fis. Soc. Ital. Sc, Modena, (2), 1, 1862, 1-36, 207.
"Oxford, Cambr. and DubUn Messenger Math., 3, 1866, 30-31.
"''Math. Quest. Educ. Times, 7, 1867, 30.
"Zeitschrift Math. Phys., 14, 1869, 121-8.
"Giomale di Mat., 9, 1871, 125-135.

456 History of the Theory of Numbers. [Chap. XX

of w, but P is not divisible by h if nh is not a multiple of m. If h divides
10"— 1, P is divisible by b when h = b, but not divisible by b when h is not a
multiple of b.

A. MoreP* proved that the numbers ending with 12, 38, 62 or 88 are the
only ones whose squares end with two equal digits.

H. Hoskins^^'* found the sum of the 117852 numbers of 7 digits which
can be formed with the digits 1, 1, 2, 2, 2, 2, 2, 3, 3, 4, 5, 6, 7.

J. Plateau^^ noted that every odd number not ending with 5 has a multiple
of the form 11... 1 [Saint^^.

P. Mansion^^ proved the theorem of Plateau.

J. W. L. Glaisher^^ deduced Crelle's^ theorem from Plateau's.^^

C. A. Laisant^^ treated a problem^ on reversing digits.

G. R. Perkins^^" and A. Martin^^ stated that all powers of numbers end-
ing with 12890625 end with the same digits.

E. Catalan^" noted that the g. c. d. of two numbers of the form 1 ... 1
of n and n' digits is of Uke form and has A digits, where A is the g. c. d. of n
and n'.

Lloyd Tanner,^"" generalizing Martin's^^ question, found how many
numbers N oin digits to the base r end with the same digits as their squares,
i. e., N^—N = Kr''. If r" is the product of q powers of primes, there are
2^ — 2 values of N. He^^^ found numbers M and N with n digits to the
base r such that the numbers formed by prefixing M to N and iV to M
have a given ratio.

J. Plateau^ ^ proposed the problem to find two numbers whose product
has all its digits alike. Angenot noted that

6^-1' 6-1

give a solution for base b. Catalan^^ noted that Euler's theorem

6-1

nm

for n prime to 6, furnishes a solution n, m.

Lloyd Tanner" stated and Laisant proved that 87109376 and 12890625
are the only numbers of 8 digits whose squares end with the same 8 digits.

"Nouv. Ann. Math., (2), 10, 1871, 44-6, 187-8.

i^Math. Quest. Educ. Times, 15, 1871, 89-91.

"BuU. Acad. Roy. de Belgique, (2), 16, 1863, 62; 28, 1874, 468-476.

"Nouv. Corresp. Math., 1, 1874-5, 8-12; Mathesis, 3, 1883, 196-7. Bull. Bibl. Storia Sc.

Mat., 10, 1877, 476-7.
"Messenger Math., 5, 1875-6, 3-5.

**M6m. 80C. sc. phys. et nat. de Bordeaux, (2), 1, 1876, 403-11.
i«»Math. Miscellany, Flushing, N. Y., 2, 1839, 92.
"Math. Quest. Educat. Times, 26, 1876, 28.
»oM6m. Society Sc. Li^ge, (2), 6, 1877, No. 4.

"•^Messenger Math., 7, 1877-8, 63-4. Cases r^ 12, Math. Quest. Educ. Times, 28, 1878, 32-4.
Jo'-Math. Quest. Educ. Times, 29, 1878, 94-5.
«Nouv. Corresp. Math., 4, 1878, 61-63.
«/Wd., 5, 1879, 217; 6, 1880, 43.

Chap. XX] PROPERTIES OF THE DiGITS OF NuMBERS. 457

Moret-Blanc^^ proved that 1, 8, 17, 18, 26, 27 are the only numbers equal
to the sum of the digits of their cubes.

C. Berdelle^^" considered the last n digits of numbers, in particular of 5*.

E. Cesaro^^ noted that the sum of the pth powers of ten consecutive
integers ends with 5 unless p is a multiple of 4, when it ends with 3.

F. de Rocquigny^^ noted that if a number of n digits equals the sum of the
2" — 1 products of its digits taken 1, 2, . . ., n at a time, its final n — 1 digits
are all 9.

E. Cesaro^® considered the period of the digits of rank n in powers of 5.

Lists^" have been given of squares formed by the nine digits > 0, or the
ten digits, not repeated.

0. Kessler^^ gave a table of divisors of numbers formed by repeating a
given set of digits a small number of times.

T. C. Simmons"" noted that, if the sum of the digits of n is 10, that of
2n is 11 unless each digit of n is <5 or two are 5. For 4 digits the numbers
of each type are counted.

J. S. Mackay^^ treated the last subject.

E. Lemoine^^ considered numbers like A = 8607004053 such that, if a is
the number derived by reversing the digits of A, the sum A+a = 12111011121
reverses into itself.

M. d'Ocagne^° considered the sum a{N) of the digits of the first N integers.
If iVp = ap-10^+ . . . +ai-10+ao and d = ap-10^-l, then

aid) = 10'-'-5a^{a,-l+9p), (7{N,) =(T{d) + {N,., + l)a^+a{N,.,).

Hence

^(iVp)=|ao(ao+l) + ia,{lO'-^-5(ai-l+97;)+iV,_i + lj-

The number of digits in 1,. . ., AT is (p+l)(iV+l)-(10^+'-l)/9. See the
next paper.

M. d'Ocagne^^ noted that, in writing down the natural numbers 1, . . .,N,
where N is composed of n digits, the total number of digits written is
n(iV+l) — In, where 1„ = 1 . . . 1 (to n digits).

E. Barbier^i" asked what is the W^^%h. digit written if the series of
natural numbers be written down.

23Nouv. Ann. Math., (2), 18, 1879, 329; proposed by Laisant, 17, 1878, 480.
23aAssoc. franQ., 8, 1879, 176-9.
\ 24Nouv. Corresp. Math., 6, 1880, 519; Mathesis, 1888, 103.

N s^Les Mondes, 53, 1880, 410-2.

26NOUV. Corresp. Math., 4, 1878, 387; Nouv. Ann. Math., (3), 2, 1883, 144, 287; 1884, 160.
»8"Math. Magazine, 1, 1882-4; 69-70; I'intermediaire des math., 4, 1897, 168; 14, 1907, 135;

Sphinx-Oedipe, 1908-9, 35; 5, 1910, 64; Educ. Times, March, 1905. Math. Quest. Educ.

Times, 52, 1890, 61; (2), 8, 1905, 83-6 (with history).
"Zeitschrift Math. Phys., 28, 1883, 60-64.
"«Math. Quest. Educ. Times, 41, 1884, 28-9, 64-5.
"Proc. Edinburgh Math. Soc, 4, 1885-6, 55-56.
"Nouv. Ann. Math., (3), 4, 1885, 150-1.
^ojornal de so. math, e ast., 7, 1886, 117-128.
"/bid., 8, 1887, 101-3; Comptes Rendus Paris, 106, 1888, 190.
""Comptes Rendus Paris, 105, 1887, 795, 1238.

458 History of the Theory of Numbers. [Chap, xx

L. Gegenbauer^^'' proved generalizations of Cantor's^- theorems, allowing
negative coefficients. Given the distinct positive integers ai, a2, . . ., every
positive integer is representable in a single way as a linear homogeneous
function of ai, a2, . . . with integral coefficients if each a^ is di\isible by a^-i
and the quotient equals the number of permissible values of the coefficients
of the smaller of the two.

R. S. .Aiyar and G. G. Storr^^*" found the number p„ of integers the sum
of whose digits (each >0) is n, by use of Pn= p„_i+ . . . +p„_9.

E. Strauss''^ proved that, if ai, ao, . . . are any integers > 1, every positive
rational or irrational number < 1 can be written in the form

— f- 1 r... (ai<ai, a2<a2, •■ •),

the a's being integers, and in a single way except in the case in which all the
a„ beginning with a certain one, have their maximum values, when also a
finite representation exists.

E. Lucas^ noted that the only numbers having the same final ten digits
as their squares are those ending with ten zeros, nine zeros followed by 1,
8212890625 and 1787109376. He gave (ex. 4) the possible final nine digits*
of numbers whose squares end with 224406889. He gave (p. 45, exs. 2, 3)
all the numbers of ten digits to base 6 or 12 whose squares end with the same
ten digits. Similar special problems were proposed by Escott and Palm-
strom in Tlntermediaire des Mathematiciens, 1896, 1897.

J. Kraus^ discussed the relations between the digits of a number
expressed to two different bases.

A. Cunningham**" called N an agreeable number of the mth order and
nth degree in the r-ary scale if the m digits at the right of 'N are the
same as the m digits at the right of A^" when each is expressed to base r;
and tabulated all agreeable numbers to the fifth order and in some cases
to the tenth. A number A of m digits is completely agreeable if the agree-
ment of A with its nth power extends throughout its m digits, the condition
being A"=A (mod r'").

E. H. Johnson^'' noted that, if a and r — \ are relatively prime and
aa. . a (to r — 1 digits to base r) is divided by r — 1 , there appear in the
quotient all the digits 1, 2, . . ., r— 1 except one, which can be found by
dividing the sum of its digits by r — 1.

C. A. Laisant^" stated that, if A = 123. . .n, written to base n+1, be
multiplied by any integer <n and prime to n, the product has the digits
of A permuted.

^"'Sitzungsber. Ak. Wiss. Wien (Math.), 95, 1887, II, 618-27.
'x^Math. Quest. Educ. Times, 47, 1887, 64. »*Acta Math., 11, 1887-8, 13-18.

»'Th6orie des nombres, 1891, p. 38. Cf. Math. Quest. Educ. Times, (2), 6, 1904, 71-2.
*Same by Kraitchik, Sphinx-Oedipe, 6, 1911, 141.
"Zeitschr. Math. Phys., 37, 1892, 321-339; 39, 1894, 11-37.

»*'British Assoc. Report, 1893, 699. »♦* Annals of Math., 8, 1893^, 160-2.

»*«L'interm6diaire des math., 1894, 236; 1895, 262. Proof by "Nauticus," Mathesis, (2), 5,
1895, 37-42.

Chap. XX] PROPERTIES OF THE DiGITS OF NUMBERS. 459

Tables of primes to the base 2 are cited under Suchanek^" of Ch. XIII.
There is a eollection^^'^ of eleven problems relating to digits.
To find^*' the number <90 which a person has in mind, ask him to
annex a declared digit and to tell the remainder on division by 3, etc.
T. Hayashi^^ gave relations between numbers to the base r:

123. . . {r-l}-(r-l)+r = l . . .1 (to r digits),

{r-ljjr-2) ...321-(r-l)-l = {r-2} jr-2) . . . (to r digits).

Several writers^*^ proved that

123. . . {r-l}-(r-2)+r-l = {r-l} . . .321.

T. Hayashi" noted that if A = 10+r(10)Hr2(10)^+ ... be multiplied or
divided by any number, the digits of each period of A are permuted cyclically.

A. L. Andreini^^" found pairs of numbers N and p (as 37 and 3) such that
the products of N by all multiples ^ (J5 — l)p of p are composed of p equal
digits to the base 5^ 12, whose sum equals the multiplier.

P. de Sanctis^^ gave theorems on the product of the significant digits of,
or the sum of, all numbers of n digits to a general base, or the numbers
beginning with given digits or with certain digits fixed, or those of other
types.

A. Palmstrom^^ treated the problem to find all numbers with the same
final n digits as their squares. Two such numbers ending in 5 and 6,
respectively, have the sum 10"+ 1. If the problem is solved for n digits,
the (n+l)th digit can be found by recursion formulae. There is a unique
solution if the final digit (0, 1, 5 or 6) is given.

A. Hauke^° discussed obscurely x'^^x (mod s'') for x with r digits to base
s. If m = 2, while r and s are arbitrary, there are 2" solutions, v being the
number of distinct prime factors of s.

G. Valentin and A. Palmstrom^^ discussed x'^^x (mod 10"), for k = 2, 3,
4, 5.

G. Wertheim^^ determined the numbers with seven or fewer digits whose
squares end with the same digits as the numbers, and treated simple prob-
lems about numbers of three digits with prescribed endings when written to
two bases.

"'iSammlung der Aufgaben . . . Zeitschr. Math. Naturw. Unterricht, 1898, 35-6.

«^«Math. Quest. Educ. Times, 6.3, 1895, 92-3.

«Jour. of the Physics School in Tokio, 5, 1896, 153-6, 266-7; Abhand. Geschichte der Math.

Wiss., 28, 1910, 18-20.
»Jour. of the Physics School in Tokio, 5, 1896, 82, 99-103; Abhand., 16-18.
"Ibid., 6, 1897, 148-9; Abhand., 21.
"oPeriodico di Mat., 14, 1898-9, 243-8.
»8Atti Accad. Pont. Nuovi Lincei, 52, 1899, 58-62; 53, 1900, 57-66; 54, 1901, 18-28; Memorie

Accad. Pont. Nuovi Lincei, 19, 1902, 283-300; 26, 1908, 97-107; 27, 1909, 9-23; 28, 1910,

17-31.
''Skrifter udgivne af Videnskabs, Kristiania, 1900, No. 3, 16 pp.
"Archiv Math. Phys., (2), 17, 1900, 156-9.
^iForhandlinger Videnskabs, Kristiania, 1900-1, 3-9, 9-13.
^^Anfangsgninde der Zahlenlehre, 1902, 151-3.

460 History of the Theory of Numbers. [Chap, xx

C. L. Bouton^ discussed the game nim by means of congruences between
sums of digits of numbers to base 2.

H. Piccioli^^" employed N = ai. . .a„ of n^3 digits and numbers a,^. . .a«„
and Qj^ . . . aj„ obtained from N by an even and odd number of transpositions
of digits. Then 2o,, . . . a«„ = laj^ . . . aj^,

W^^ a number of n digits to base R has r fixed digits, including the first,
and the sum of these r is = — a (mod R — l), the number of ways of choosing
the remaining digits so that the resulting number shall be divisible by R — l
is the number of integers of n — r or fewer digits whose sum is = a (mod R — l)
and hence is A^'+l or N, according as a=0 or a>0, where N= (/2"~'' — 1)

G. Metcalfe^^'' noted that 19 and 28 are the only integers which exceed
by unity 9 times the integral parts of their cube roots.

A. Tagiuri^ proved that every number prime to the base g divides a
number 1 ... 1 to base g (generalization of Plateau's^^ theorem) .

If"^" A, B, C have 2, 3, 4 digits respectively and A becomes A' on re-
versmg its digits, and 2A-1 = A', SB-2A + 10=B', 4C-B-\-l + [B/10]
= C, then A = 37, B= 329, C= 2118.

P. F. Teilhet^^ proved that we can form any assigned number of sets,
each including any assigned number of consecutive integers, such that with
the digits of the ^th power of any one of these integers we can form an
infinitude of different qth. powers, provided q<m, where m is any given
integer.

L. E. Dickson^*" determined all pairs of numbers of five digits such that
their ten digits form a permutation of 0, 1,. . ., 9 and such that the sum
of the two numbers is 93951.

A. Cunningham^^'' found cases of a number expressible to two bases by a
single digit repeated three or more times. He^^" noted that all 10 digits or
all >0 occur in the square of 10101010101010101 or of 1 . . .1 (to 9 digits),
each square being unaltered on reversing its digits.

He^^*^ and T. Wiggins expressed each integer ^ 140 by use of four nines,
as 13 = 9+ V9+9/9, allowing also .9 = 1, ( V9) !, and the exponent V9, and
cited a like table using four fours.

j£45c ^= I (mod q), 1 ... 1 (with q^ digits to base r) is divisible by q"".

W^^ the square of a number n of r digits ends with those r digits, then
10''+1 — n has the same property. Also, {n — iy ends with the same r digits

«Annals of Math., (2), 3, 1901-2, 35-9. GeneraUzed by E. H. Moore, 11, 1910, 93-4.

^^'Nouv. Ann. Math., (4), 2, 1902, 46-7.

"''Math. Quest. Educ. Times, (2), 1, 1902, 119-120.

*'^Ibid, 63-4.

"Periodico di Mat., 18, 1903, 45.

«*<»Math. Quest. Educ. Times, (2), 5, 1904, 82-3.

**L'interm6diaire dea math., il, 1904, 14-6.

""Amer. Math. Monthly, 12, 1905, 94-5.

"''Math. Quest. Educ. Times, (2), 8, 1905, 78.

*^Ibid, 10, 1906, 20. «<iMath. Quest. Educ. Times, 7, 1905, 43-46.

««7Wd., 7, 1905, 49-50. *^flbid., 7, 1905, 60-61.

Chap. XX] PROPERTIES OF THE DiGITS OF NXH^BERS. 461

as 71 — 1. If the cube of a number n of r digits ends with those r digits,
W—n has the same property.

P. Ziihlke^® proved the three theorems of Palmstrom^^ and gave all solu-
tions of x^^x (mod 10^) for p = 3,. . ., 12.

M. Koppe^^ noted that by prefixing a digit to a solution 0, 1, 5 or 6
of x^=x (mod 10) we get solutions of a;^=a; (mod 10^), then for 10^, etc. We
can pass from a solution with n digits for 10" to solutions with 2n digits
for 10^". He treated also x^=x (mod 10").

G. Calvitti^^ treated the problem: Given a number A, a set C of 7 digits,
and a number p prime to the base g, to find the least number x of times the
set C must be repeated at the right of A to give a number Nx=A (mod p).
The condition is G{Ni—No)=0 (mod p), where

o^"^ — 1

If iVi— iVo=0, any x is a solution. If not, the least value X of a: makes
G=0 (mod p/p), where p is the g. c. d. of Ni — Nq and p. Then X is the
1. c. m. of Xi, . . . , X;t, where X^ is the least root of G=0 (mod Pi), if p/p is the
product of pi, . . . , Pk, relatively prime in pairs. Hence the problem reduces
to the case of a power of a prime p. Write (a)^ for (a^ — l)/(a — 1). It is
shown that the least root of (a)j.= 0 (mod p'') is mp^~\ where m is the least
root of (a)^=0 (mod p), and p' is the highest power of p dividing (a)^.
Given any set C of digits and any number p prime to the base g, there exist
an infinitude of numbers C . . .C divisible by p.

A. G^rardin^^'' added 220 to the sum of its digits, repeated the operation
18 times and obtained 418; 9 such operations on 284 gave 418. A. Boutin
stated that if a and b lead finally to the same number, neither a nor 6 is
divisible by 3, or both are divisible by 3 and not by 9, or both are divi-
sible by 9.

E. Malo^^ considered periodicity properties of A and a in

5' = 10'"A„.p+ap (ap<10^ k=n-2'^-^+p, 0^p^2"'-^-l) ,

and solved Cesaro's^^ three problems on the digits of powers of 5.

A. L. Andreini^° noted that the squares of A and B end with the same
p digits if and only if the smaller of r+s and u-\-v equals p, where

iH-J5 = a-2'^-5", A-B=^-T-5''

«Sitz. Berlin Math. Gesell., 4, 1905, 10-11 (Suppl., Archiv Math. Phys., (3), 8, 1905).

"Ibid., 5, 1906, 74-8. (Suppl., Archiv, (3), 11, 1907.)

"Periodico di Mat., 21, 1906, 130-142.

""Sphinx-Oedipe, 1, 1906, 19, 47-8. Cf. I'interm^d. math., 22, 1915, 134, 215.

*'Sur certaines propri6t6s arith. du tableau des puissances de 5, Sphinx-Oedipe, 1906-7, 97-107;

reprinted, Nancy, 1907, 13 pp., and in Nouv. Ann. Math., (4), 7, 1907, 419-431.
"II Pitagora, Palermo, 14, 1907-8, 39-^7.

462 History of the Theory of Numbers. [Chap, xx

W. Janichen^"'* stated that, if qp{x) denotes the sum of the digits of x to
the base p and if p is a prime divisor of n, then, for /j, as in Ch. XIX,

s.W,.6) =

0.

E. N. Barisien^"'" noted that the sum of all numbers of n digits formed
with p distinct digits f^O, of sum s, is

s(p + 1)"-Mp(10"-^-1)/9 + (p + 1)10"-^).

A. G^rardin^"'' listed all the 124 squares formed of 7 distinct digits.

Several writers^^ treated the problem to find four consecutive numbers
a^ 6 = a + l, c = a+2, d = a-\-3, such that (a)i = ll . . .1 (to a digits) is divisible
by a + 1, (6)i by 26 + 1, (c)i by 3c+l, (d), by 4d+l.

A. Cunningham and E. B. Escott^- treated the problems to find integers
whose squares end with the same n digits or all with n given digits; to find
numbers having common factors with the numbers obtained by permuting
the digits cyclically, as

259 = 7-37, 592 = 16-37, 925 = 25-37.

E. N. Barisien^^ noted that the squares of 625, 9376, 8212890625 end
with the same digits, respectively. R. Vercellin^^ treated the same topic.

E. Nannei^^ discussed a problem by E. N. Barisien: Take a number of
six digits, reverse the digits and subtract; to the difference add the number
with its digits reversed; we obtain one of 13 numbers 0, 9900, . . . , 1099989.
The problem is to find which numbers of six digits leads to a particular one
of these 13, and to generalize to n digits.

Several writers^^ examined numbers of 6 digits which become divisible
by 7 after a suitable permutation of the digits ; also^^ couples of numbers,
as 18 and 36, 36 and 54, whose g. c. d. 18 is the sum of their digits.

E. N. Barisien^^ gave ten squares not changed by reversing the digits,
as676 = 26^

A. Witting^^ noted that, besides the evident ones 11 and 22, the only
numbers of two digits whose squares are derived from the squares of the
numbers with the digits interchanged by reversing the digits are 12 and 13.
Similarly for the squares of 102 and 201, etc. Also,

102-402 = 201 -204, 213-936 = 312-639, 213-624 = 312-426.

A. Cunningham^" treated three numbers L, M, N of I, m, n digits,
respectively, such that N = LM, and A^ has all the digits of L and M and no
others.

"^Archiv Math. Phys., (3), 13, 1908, 361. Proof by G. Szego, 24, 1916, 85-6.

'ocSphinx-Oedipc, 1907-8, 84-86. For p = n. Math. Quest. Educ. Times, 72, 1900, 126-8.

•tx^/bid., 1908-9, 84-5.

"L'intermddiaire des math., 16, 1909, 219; 17, 1910, 71, 203, 228, 286 [136].

"Math. Quest. Educat. Times, (2), 1.5, 1909, 27-8, 93-4.

"Suppl.alPeriodicodiMat., 13, 1909,20-21. "Suppl.alPeriodicodiMat., 14, 1910-11, 17-20.

"/bid., 13, 1909, 84-88. ^«L'interm6diaire des math., 17, 1910, 122, 214-6, 233-5.

"Ibid., 170,261-4; 18, 1911,207. "Mathesis, (3), 10, 1910, 65.

"Zeitschrift Math.-Naturw. Unterricht, 41, 1910, 45-50.

"Math. Quest. Educat. Times, (2), 18, 1910, 23-24.

Chap. XX] PROPERTIES OF THE DiGITS OF NUMBERS. 463

D. Biddle®^ applied congruences to find numbers like 15 and 93 whose
product 1395 has the same digits as the factors.

P. Cattaneo^^ considered numbers Q (and C) whose square (cube) ends
with the same digits as the number itself. No Q>\ ends with 1. No two
Q's with the same number of digits end with 5 or with 6. All Q's < 10^* are
found. A single C of n digits ends with 4 or 6. Any Q is a C Any Q — 1
is a C. If A?" is a Q with n digits and if 2N — 1 has n digits, it is a C.

M. Thie,^^" using all nine digits >0, found numbers of 2, 3 or 4 digits
with properties like 12483 = 5796.

Pairs^^*^ of cubes 3^ 6^ and 375^ 387^ whose sums of digits are squares,
32 and 61

T. C. Lewis^^ discussed changes in the digits of a number to base r not
affecting its divisibiUty by p.

Numbers^'* B and 5" having the same sum of digits.

Pairs^^ of primes like 23-89 = 29-83.

Cases<^« like 7-9403 = 65821 and 3-1458 = 6-0729, where the digits 0,
1,. . ., 9 occur without repetition.

jy-pn+i ending" with the same digits as A^.

Numbers^^ like 512 = (5+l+2)^ 47045881000000 = (47+4+58+81)^

AlP numbers like 2-5-27 = M8-15, 2+5+27 = 1 + 15 + 18.

Number^° divisible by the same number reversed.

Number^^ an exact power of the sum of its digits; two numbers each
an exact power of the sum of the digits of the other.

Solve'^^ KN-{-P = N', N' derived from N by reversing the digits.

Symmetrical numbers (ibid., p. 195).

F. Stasi^^ proved that, if a, h are given integers and a has m digits, we
can find a multiple of b of the form

10''(a-10'"'+a-10"^^'-^^+ . . . +a), p^O.

Taking b prime to a and to 10, we see that b divides 10""'+ ... +1. The
case m= 1 gives the result of Plateau. ^^

Cunningham'^^" and others wrote iVi for the sum of A^ and its digits to
base r, iV2 for the sum of A^i and its digits, etc., and found when N^ is
divisible by r — 1 . •

"Math. Quest. Educ. Times, (2), 19, 1911, 60-2. Cf. (2), 17, 1900, 44.

«2Periodico di Mat., 26, 1911, 203-7.

fi^^Nouv. Ann. Math., (4), 11, 1911, 46.

62''Sphinx-Oedipe, 6, 1911, 62.

"Messenger Math., 41, 1911-12, 185-192.

6*L'intermMiaire des math., 18, 1911, 90-91; 19, 1912, 267-8.

^Ubid., 1911, 121, 239. ««/6id., 19, 1912, 26-7, 187.

"Ibid., 50-1, 274-9.

^^Ibid., 77-8, 97.

«9/6id., 125, 211.

''"Ibid., 128.

''Ibid., 137-9, 202; 20, 1913, 80-81.

"76id., 221.

"II Boll. Matematica Gior. Sc.-Didat., 11, 1912, 233-5.

73«Math. Quest. Educ. Times, (2), 21, 1912, 52-3.

"L'interm^diaire des math., 20, 1913, 42-44.

^^Ibid., 80.

'*Ibid., 124, 262, 283-4.

"Atti Accad. Romana Nuovi Lincei, 66, 1912-3, 43-5.

"Archiv Math. Phys., (3), 22, 1914, 365-6.

"Giomale di Mat., 52, 1914, 53-7.

'"L'interm^diaire des math., 21, 1914, 23^, 58.

"/6id., 22, 1915, 110-1. Objections by MaUlet, 23, 1916, 10-12.

"Suppl. al Periodico di Mat., 19, 1915, 17-23.

"''Sphinx-Oedipe, 9, 1914, 42.

"Sitzungsber. Berhn Math. Gesell., 15, 1915, 8-18.

"Nouv. Ann. Math., (4), 17, 1917, 234.

"L'intermddiaire des math., 24, 1917, 31-2.

»/Wd., 96. Cf. H. Brocard, 25, 1918, 35-8, 112-3.

I

464 History of the Theory of Numbers. [Chap, xx

A. Cunningham"^ listed 63 symmetrical numbers aoaia2aiao each a
product of two symmetrical numbers of 3 digits, and all numbers n^,
r2< 10000, and all n'\ n\ n^, n^\ 7i<1000, ending with 2, 7, 8, symmetrical
with respect to 2 or 3 digits, as 618' = 236029032. f ie^'

Pairs'^ of numbers whose 1. c. m. equals the product of the digits.

Pairs'^ of biquadrates, cubes and squares having the same digits.

*P. de Sanctis'^ noted a property of numbers to the base h^+1.

L. von Schrutka^^ noted that 15, 18, 45 in 7-15 = 105, 6-18 = 108 and
9-45 = 405 are the only numbers of two digits which by the insertion of
zero become multiples.

G. Andreoli^^ considered numbers N of n digits to the base k whose rth
powers end with the same ?i digits as N. Each decomposition of k into
two relatively prime factors gives at most two such N's. If the base is a
power of a prime, there is no number > 1 whose square ends with the same
digits.

Welsch^° discussed the final digits of pth powers.

H. Brocard^ ^ discussed various powers of a number with the same sum
of digits. _

A. Agronomof®^ wrote N for the number obtained by reversing the digits
of N to base 10 and gave several long formulas for 2ji J j.

The^-'' only case in which N^—N"^ is a square for two digits is 65- —
56^=33". There is ^o case for three digits.

R. Burg^ found the numbers N to base 10 such that the number
obtained by reversing its digits is a multiple kN of A^, in particular for
A: = 9, 4.

E. Lemoine^ asked a question on sjinmetrical numbers to base b.

H. Sebban^^ noted that 2025 is the only square of four digits which yields
a square 3136 when each digit is increased by unity. Similarly, 25 is the
only one of two digits.

R. Goormaghtigh^^ noted that this property of the squares of 5, 6 and
45, 56 is a special case of A^—B"^ — !. . .1 (to 2p digits), where A = 5. . .56,
5 = 4. . .45 (to p digits). Again, the factorizations 11111=41-271, 1111111
= 239-4649 yield the answers 115^, 156^ and 2205^, 2444^.

I

1

Chap. XX] PROPERTIES OF THE DiGITS OF NUMBERS. 465

SeveraP^" gave 9'w!+n+l= 1 . . .1 for n^9, with generalization to any
base.

E. J. Moulton^^ found the number of positive integers with r+1 digits
fewer than p of which are unity (or zero). L. O'Shaughnessy^^ found the
number of positive integers < 10* which contain the digit 9 exactly r times.

Books^^ on mathematical recreations may be consulted.

F. A. Halliday^^ considered numbers N formed by annexing the digits
of B to the right of A, such that N= (A+B^, as for 81= (8 + 1)1 Set
N=A-W+B. Then A{W-1)= iA+B)(A-}-B-l), so that it is a ques-
tion of the factors of lO'' — 1.

*J. J. Osana^^ discussed numbers of two and three digits.
E. Gelin^^ listed 450 problems, many being on digits.

*^"L'intermediaire des math., 2.5, 1918, 44-5.

"Amer. Math. Monthly, 24, 1917, 340-1.

8«/6id., 25, 1918, 27,

*^E. Lucas, Arithmetique amusante, 1895. E. Fourrey, Recreations Arithmetiques, 1899.

W. F. White, Scrap-Book of Elem. Math., etc.
90Math. Quest, and Solutions, 3, 1917, 70-3.
siRevista Soc. Mat. Espafiola, 5, 1916, 156-160.
92Mathesis, (2), 6, 1896, Suppl. of 34 pp.

AUTHOR INDEX.

The numbers refer to pages. Those in parenthesis relate to cross-references,
brackets refer to editors or translators. The other numbers refer to actual reports.

Those in

Ch. I. Perfect, Multiply Perfect, and Amicable Numbers.

Algafd, 39
Alcuin, 4
Alkalacadi, 40
Allemanno, 39
Ankin, 5
Anonymous, 47
Aristotle, 38
Astius, [3]
Aubry, 31, 33
Augustinus, 4
Azulai, 39

Bachet, 10
Bachmann, 33
Baeza, 9
BaU, 12, 32
Ben Kalonymos, 39
Ben Korrah, 5, 39
Bezdi^ek, 32, 48
Bickmore, 28
Boethius, 4 (5-7, 11)
Bourlet, 28 (29)
BoviUus, 7 (6, 10, 32)
Bradwardin, 6
Brassinne, [12, 36]
Brocki, 11
Bronckhorst, 8
Broscius, 11, 13, 36 (41)
Bulhaldo, [3]
Bungus, 9, 40 (10-15)

Capella, 11

Cardan, 8, 40 (11, 14)
Carmichael, 29, 37, 38 (35)
Carvallo, 22, 24 (26)
Catalan, 22, 24, 26, 27, 32, 48

(28, 49)
Cataldi, 10 (7)
Cesaro, 26
Chevrel, 27, 48
Christie, 27
Chuquet, 6, 40
Ciamberlini, 29
Cipolla, 29, 33
Cole, 29 (13, 22, 25, 27, 32)
Cunningham, 27, 28, 29, 30,

31, 37, 48 (21, 32)
Curtze, [6]

De Backer, [11]
De la Roche, 8, 40

De Longchamps, 22
De Neuveghse, 15
Desboves, 23, 37 (21, 25)
Descartes, 12, 33, 34-36,

40-42 (37, 46)
De Slane, [39]
De Tovmes, [8]
Dickson, 30-32, 49, 50
Dombart, [4]
Dupuis, 48

El Madschritt, 39
El Magritl, 39
Enestrom, 46
Ens, 11 (16, 19)
Escott, 50
EucHd, 3

Euler, 17-19, 41-46 (12, 14,
16, 22-28, 31, 47-50)

Faber Stapulensis, 6 [5]
Fauquembergue, 27, 30-32

(28, 29)
Feliciano, 7
Fermat, 12, 33, 34, 36, 37, 40

(18)
Ferrari, 33

Fibonacci (see Leonardo)
Fitz-Patrick, 27, 33, 48 [28]
Fontana, 20 (17)
Font^s, 32 [9]
Forcadel, 9
Frenicle, 12, 14, 35 (13, 19,

28, 31)
Fried lein, [4]
Frizzo, (4) [8]
Fuss, 46 [15, 18]

Genaille, 27

G^rardin, 29-32, 48-50 (21)

Gerhardt, [6]

Ginsburg, [5, 39]

Giraud, 33

Goldbach, 15

GosseUn, [9]

Gough, 47

Goulard, 28

Graevius, [11]

Griison, 20, 47 (16)

Giideman, [5]

Haas, 48

Halcke, 41

Hammond, 30

Hankel, [4]

Hansch, 17 (18, 19)

Harris, 16

Hebrews, 3

Heilbronner, 18

Heinlin, 14

Henischiib, 10

Henry, [10, 12, 36, 40]

HiU, 16 [20]

HiUer, [3]

Hoche, [3]

Hrotsvitha, 5

Hudelot, 25

Hultsch, 32

Himrath, 43

Button, [16, 18, 19, 36, 47]

Huygens, [14]

lamblichus, 4, 38 (15, 32)

Ibn Albanna, 40

Ibn el-Hasan, 39

Ibn Ezra, 5

Ibn KJialdoun, 39

Ibn Motot, 5

Isidorus, 4

Jacob, 39
Jordanus, 5 (6, 7)
Jumeau (see St. Croix)

Kastner, 16

Kiseljak, 33

Klugel, 47

Kraft, 17-19, 41, 50 (8, 9, 20,

46, 47)
Kraitchik, 22, 25, 47 (32)
Kummer, [21]

Landen, 18 (41)
Landry, 21-23 (25)
Lantz, 11
Lax, 7

Lazzarini, 29
Lebesgue, 20 (23)
Ijcfevre (see Faber)
Legendre, 36, 47 (27, 35)
Lehmer, 37 (36)
Leibniz, 15

467

468

Author Index

Le Lasseur, (21, 23-25, 28,

48)
Leonardo Pisano, 5
Leuneschlos, 14
Leurechon, 11

Lcybourn, 15, 41 [16, 18, 47]
Libri, [10]
Liebnecht, 16
Lionnet, 23 (19)
LiouviUe, (19)
Lucas, 14, 15, 22-25, 27, 28,

37,40(12, 17, 19, 21, 29-

32, 35, 36, 48)

Magnin, [5]

Mahnke, [15]

Maier, 17 (20)

Malcolm, 16

Mandey, [14]

Mansion, 24, 26

Manuscript, 6

Marre, [6]

Martinus, 7

Maser, [36, 47]

Mason, 32, 38

Maupin, [7]

Maurolycus, 9 (20)

McDonnell, 32

Meissner, 49

Mersenne, 12, 13, 33, 35, 36,

40, 41 (14, 15, 18, 20, 22,

25, 27, 28, 31, 32)
Migne, [4]

Montucla, 19 (16, 36)
Moret-Blanc, 23
Munyos, 4

Nachshon, 39
Nassd, 32
Neomagus, 8
Nicomachus, 3 (4)
Niewiadomski, 32
Nocco, 21 (26)
Novarese, 25 (26)
Noviomagus, 8

Oughtred [11]

Ozanam, 15-17, 36, 41(19, 20)

Paciuolo, 6, (10, 19)

Paganini, 47 (49)

Pauli, 15

Peacock, 50

Peletier, 8

Pellet, 25

Pepin, 23, 28, 47

Perrott, 48

Pervnisin, 25

Philiatrus, 15

Philo, 3

Pistelli, [4]

Plana, 21 (17, 22, 24, 29)

Poggendorff, [11]

Postello, 9

Poulet, 50

Powers, 30, 32 (22)

Prestet, 15

Pudlowski, 12

Puteanus, 11 (14)

Putnam, 30

Pythagoreans, 4, 5, 38

Ramesam, 31
Ramus, 9
Recorde, 9, 33
Regius, 7

Reuschle, 21 (24, 31)
Ricalde, 32
Rubin, [3]
Rudio, 45
Ruffus, 7

Saverien, 19
Schonero, [9]
Schooten (see Van)
Schubert, 32
Schwenter, 11, 40, 50
Seelhoflf, 25, 48 (29)
Sempilius, 11
Semple, 11
Servais, 26 (25)
Spoletanus, 7

St. Croix, 34
Steinschneider, [5, 39]
Stern, 25 (19)
Stifel,8, 40(11, 17, 41)
Stone, 41
Struve, 20, 47
Studni^ka, 28
Stuj'vaert, 28
Suter, [39]
Sylvester, 26, 27 (19, 31)

Tacquet, 14

Tannery, 28

Tarry, 30

TartagUa, 9, 40 (11, 17)

Tassius, 15

Taylor, 20, 50

Tchebychef, 47

Tennulius, 15 [4]

Terquem, 20

Thabit (see Ben Korrah)

Theon of Smyrna, 3

Turcaninov, 29

Turtschaninov, 29

Unicornus, 10

Vaes, 33

Valentin, 25

Valla, 6

Van Etten, 11

Van Schooten, 14, 41 (42, 47)

Von Graffenried, 10

Wantzel, 20 (17)
Waring, 46
Wertheim, 33 [10]
Westerberg, 20
Westlund, 37, 38
WiUibaldus, 11
WiUichius, 8
Winsheim, 18 (17)
Woepcke, [5, 39]
Wolf, 16 (17)
Woodall, 30 (28, 32)

Young, [3]

Ch. II. Formulas for the Number and Sum of Divisors, Problems of Fermat

AND Wallis.

Bang, 56
BernouUi, 55
Blaikie, 58
Brocard, 57
Brouncker, 54

Cantor, 53
Cardan, 51
Castillionei, 51

Chalde, 52
Cunningham, 58

Deidier, 52

De Montmort, 52

Descartes, 52, 53

Escott, 54
Euler, 54

Fauquembergue, 57
Fermat, 53, 54, 56 (57)
Fontend, 52
Frenicle, 53, 55 (56)

Genocchi, 57
G^rardin, 57, 58
Gerono, 56

Author Index

469

Hain, 52
Halcke, 58
Henry, [53, 54, 56]
H^v^lius, 54
Hoppe, 51

Kersey, 51
Kraft, 53
Kronecker, 54

Landau, 57
Lionnet, 52, 58
Lucas, 55-58

Mersenne, 51, 53
Minin, 52
Moreau, 57
Moret-Blanc, 57

Newton, 51 (53)

Ozanam, 56

Peano, 53
Plato, 51
Prestet, 52
Pujo, 52

Rudio, 54

Stifel, 51

Vacca, 57

Van Schooten, 51, 55

Wallis, 51, 53-56
Waring, 52, 54, 55
Wertheim, 54
Winsheim, 51
Wolff, 54

Ch. III. Fermat's and Wilson's Theorems, Generalizations and Converses;
Symmetric Functions of 1, 2,..., p-1 Modulo p.

Allardice, 96

Anton, 75

Anonymous, 67, 70, 92

Arevalo, 83

Arndt, 71, 72 (77, 81, 82)

Arnoux, 81, 94

Aubry, 81, 101 (71, 103)

Axer, 86

Bachmann, 72, 81, 82, 95 (78)

Banachiewicz, 94

Bauer, 88, 89

Beaufort, 62

Beaujeux, 75

Binet, 67

Birkenmajer, 96

Blissard, 74

Borel and Drach, 85, 87 (89)

Bossut, [63]

Bottari, 83

Bouniakowsky, 67, 73, 92, 95

(89, 93)
Brennecke, 69, 73 (80)
Bricard, 81 (75, 82)

Cahen, 80, 103

Candido, 80

Cantor, 62

Capelli, 80, 89

Caraffa, 69

Carmichael, 82, 94 (78, 86,

95)
Carre, 60

Catalan, 71, 77, 98
Cauchy, 67, 69, 70, 95 (86)
Cayley, 76 (75, 83)
Cesaro, 98
Chinese, 59, 91
CipoUa, 93, 94
Concina, 101
Cordone, 85
Crelle, 68, 70, 71, (72)

Cunningham, 94

D'Alembert, 63

Daniels, 78

Dedekind, [74]

De la Hire, 60

Del Beccaro, 79

De Paoli, 67 (79, 82)

D'Escamard, 81

Desmarest, 73

Dickson, 80, 85, 89

Dirichlet, 66, 74 (65, 68, 71,

73, 77, 80, 81, 84)
D'Ocagne, 79, 98
Donaldson, 82
Diu-ege, 73

Earnshaw, 70
Eisenstein, 95
Epstein, (86)
Escott, 93, 94, 103
Euler, 60-65, 92 (66, 67, 69,
72-74, 76, 77, 81-83)

Fergola, 96 (97, 98)
Fermat, 59 (60, 94)
Ferrers, 79, 99
Fontebasso, 74
Franel, 93
Frattini, 84
Frost, 96 (100)

Garibaldi, 77

Gauss, 60, 65, 84 (67, 69, 71,

72, 74, 75, 82, 83, 101)
Gegenbauer, 86, 93, 99
Genese, 78
Genty, 64
Gerhardt, [59]
Glaisher, 99, 100 (102, 103)
Goldbach, 92
Gorini, 70
Grandi, 85

Graves, 73
Gruber, 87

Grunert, 66-68, 71, 72 (65,
73, 81)

Harris, 81
Hayashi, 93
Heal, 77
Heather, 72
Hensel, 91, 101
Horner, 66, 69 (68, 71, 73, 74,
82)

lllgner, 83
Irwin, 103
Ivory, 65 (66-69, 71, 74)

Jacobi, 90 (91)
Janssen van Raay, 101
Jeans, 93 (59, 91)
Jolivald, 93
Jorcke, 76

Kantor, 84
Klugel, [67]
Koenigs, 85
Korselt, 93
Kossett, 93
Kraft, 60
Kronecker, 80, 88

Lacroix, 65, [63]

Lagi-ange, 62 (59, 64, 73, 74,

97, 99)
Laisant, 75 (76, 78)
Lambert, 61, 92
Laplace, 63 (67, 73, 82)
Lebesgue, 74, 96
Legendre, 64 (80)
Leibniz, 59, 60, 91 (65, 70, 94)
Leudesdorf, 96
LeVavasseur, 88

470

Author Index

Levi, 79, 93
Libri, 69 (101)
Lindsay, 82
Lionnet, 71, 98
Lista, 73
Lottner, 73

Lucas, 77, 78, 85, 92, 99 (81,
82, 86, 93, 94)

MacMahon, 78, 85, 86
Mahnke, 59, 94 (91)
Maillct, 78, 85
Malo. 88, 93
Mansion, 76
Maser, [65]
Mason, 102
Meissner, 102 (101)
Meyer, 101
Midy, 69
MUler, 81

Minding, 68 (71, 77)
Minetola, (66)
MitcheU, 98, (86, 87)
Monteiro, 100
Moore, 87 (88, 89)
Moreau, 80 (67, 81, 86)
Morehead, 94
Moret-Blanc, 98

Nicholson,'81, 101

Nielsen, 62, 89, 96, 99, 102,

103 (87) '
Niewenplowski, 96

Osbom, 96, 99
Ottinger, 75

Peano, [59]
Pellet, 85

Perott, 80, 88, 99 (75)

Petersen, 75 (76, 80, 81)

Petr, 81

Piccioli, 84

Picquet, 85

Pincherle, 80

Plana, 74

Pocklington, 82

Poinsot, 71, 95 (72, 76, 101)

Pollock, 73

Poselger, 66

Prompt, 81, 83

Proth, 92

Prouhet, 72

Putnam, 102

Rawson, 99
Ricalde, 93
Rieke, 96
Rogel, 87

Sardi, 74, 97
Sarrus, 92
Sauer, 89
Scarpis, 81, 82
Schaflfgotsch, 64 (65)
Schapira, 93
Schering, 76 (80, 81)
Scherk, 90, 91
Schlomilch, 73
Schmidt, 79
Schonemann, 69, 84
Schubert, 64
Schuh, 83
Schumacher, 83
Serret, 73, 84, 96 (100)
Sharp, 96
Sibirani, 100
Steiner, 90 (91)

Stern, 74

Sylvester, 69, 73, 96, 98 (79,

81, 97)

Talbot, 74
Tarrj', 65

Tchebychef, 73 (77, 100)
Terquem, 71
Thaarup, 92
Thue, 79, 82
ToepUtz, 74
Torelli, 97 (98)
Tschistjakov, 82

Unferdinger, (75)

Vacca, 59
Valentiner, 96
V%i, 86
Vandiver, 89, 93
Verhulst, 66
Von Schaewen, 76
Von Staudt, 95
Von Stemeck, 80

Waring, 62, 64, 95 (81)
Weber, 80
Welsch, 95
Wertheim, 77, 101
Western, 94
Westlund, 86, 100
Weyr, 85

Wildschiitz-Jessen, 84
Wilson, 62 (59)
Wolstenhohne, 96 (99, 103)

ZeUer, 76
Zsigmondy, 93

Ch. IV. Residue of {vP-'^ — l)/p Modulo p.

Abel, 105
Aladow, 107

Bachmann, 109, 111
Baker, 110
Bastien, 111
Beeger, 111
Brocard, 111

Cunningham, 107,110

De Romilly, 108
Desmarest, 105 (106)

Eisenstein, 105 (106)
Euler, 112 (106)

Fauquembergue, 111

Friedmann, 110
Frobenius, 110 (HI)

Gegenbauer, 106
G^rardin, 112
Glaisher, 108, 109
Grave, 110 (111)

Hertzer, 110

Jacobi, 105 (111)
Janssen van Raay, 110

Lerch, 109, 110 (112)
Lucas, 106

Meissner, 111, 112 (106, 110)
Meyer, 107

Mirimanoff, 107, 110 (109,
111)

Nielsen, 112

Palmstrom, 108
Panizza, 106
Plana, 106 (109, 112)
Pleskot, 109
Pollak, 108
Proth, 106 (111)

Stem, 106 (109)
Sylvester, 105 (106-110)

Tamarkine, 110
Tarry, 111
Thibault, (105)

Vandiver, 112 (111)
Verkaart, 111

Wieferich, 110 (111)

Author Index

471

Ch. V. Euler's ^-Function, Generalizations, Farey Series.

Airy, 157
Alasia, 119
Anonymous, 158
Arndt, 116, 118 (140)
Arnoux, 151
Axer, 138 (157)

Bachmann, 124, 132, 147, 158

Bauer, 134

Berger, 131

BernoulU, 140

Betti, 120

Binet, 141 (142, 146)

Blind, 142, 148

Bonse, 137 (132)

Borel and Drach, 120, 133

Bougaief, 142 (145)

Brennecke, 141 (143)

Brocot, 156

Busche, 130, 137, 155, 158

Cahen, 140, 155, 158
Cantor, 125 (122, 149)
Carlini, 136, 150, 153
Carmichael, 137, 155
Catalan, 116, 124, 130, 143

(117, 118)
Cauchy, 116, 140, 156
Cayley, 121
Ces^ro, 127-130, 143-145,

148-150 (126, 138, 140, 153,

157)
Chrystal, 120
Cistiakov, 151
Composto, 138
Concina, 131
Cordone, 155
Crelle, 115, 117, 140 (118,

119, 121, 132, 137, 139,

141, 143)
Crone, 125
Cunningham, 140
Curjel, 126

Da Silva, 119, 141

Davis, 132

Dedekind, 120, 123 (140)

Del Beccaro, 146

De Rocquigny, 124, 143

Desmarest, 116

De Vries, 134

Dirichlet, 119, 122 (121, 126,

127, 130, 132-134, 136, 150,

152, 154)
D'Ocagne, 157
Druckenmiiller, 116

Eisenstein, 156

Elliott, 135

Euler, 113, 114 (115-118, 122,
138, 146)

Farey, 156
Fekete, 137
Fleck, 139
Flitcon, 155
Fontebasso, 122 (120)

Gauss, 114 (116-118, 122,

133, 142, 147)
Gegenbauer, 122, 129, 145,

146, 149, 151, 152 (142,

150, 155)
Glaisher, 146, 148, 157 (150,

158)
Goldschmidt, 132, 147
Goodwyn, 156
Goormaghtigh, 140
Grunert, 117 (134)
Guilmin, 119 (118)

Halphen, 126, 156 (132)
Hammond, 131, 139, 140, 149

(133)
Hancock, 139
Haros, 156
Harris, 143
Hensel, 135, 139
Hermes, 158
Herzer, 156
Horta, 119
Hrabak, 156
Humbert, 158
Hurwitz, 158

Jablonski, 131, 151

Jensen, 130

Jordan, 147 (123, 132)

Kaplan, 134
Klein, 158
Knopp, (140)
Kronecker, 135 (155)
Kuyver, 139

Laguerre, 122 (129, 133, 152)
Landau, 134, 136, 138 (132)
Landry, 119
Landsberg, 136
Lebesgue, 118, 121
Legendre, 114 (116, 118, 121,

132, 143, 145)
Lehmer, 153 (157)
Le Paige, 124

Lerch, 136
Leudesdorf, 145
LiouviUe, 120, 142 (127, 144)
Lipschitz, (140)
Lucas, 125, 131, 142, 147, 157,
158 (123, 126, 137)

MacMahon, 131

Made, 158

Maillet, 134 (132, 137, 138)

Mansion, 123, 124, 128 (127)

Mathews, 120

Mennesson, 143

Merrifield, 156

Mertens, 122 (126, 127, 132,

154)
Metrod, 155
Miller, 137, 138, 155
Minding, 116 (118)
Minin, 133, 155 (140)
Minine, 124, 143, 144, 157

(145)
MitcheU, 125
Moreau, 131, 134 (136)
Moret-Blanc, 122, 144

Nasimof, 145 (146)
Nazimov (Nasimof)
Nielsen, 146
Nordlund, 137

Occhipinti, 136
Oltramare, 142
Orlandi, 138
Orlando, 137

Pepin, 122 (151)
Perott, 126 (127, 131)
Pichler, 134 (137)
Poinsot, 117 (114)
Poretzky, 130
Postula, 143

Prouhet, 118, 140 (131, 150)
Pullich, 157

Radicke, 125
Ranum, 137
Ratat, 140
Remak, 138 (132)
Rogel, 126, 133, 134 (140)

Sanderson, 155
Sang, 157
Scar pis, 139

Schatunowsky, 132 (134)
Schemmel, 147
Sierpinski, 158

472'

Author Index

Smith, 122 (123, 124, 127,

128, 130, 136)
Sommer, 137
Steggall, 132 (118)
Stem, 156 (157)
Stor>', 148
Stouvencl, 156
Sturm, 120
Suzuki, 137
Sylvester, 121, 124, 126, 133,

157 (115, 129, 132, 154,

155)

Tanner, 131
Tchebychef, 119 (132)
Thacker, 140 (123, 142, 144-

147)
Tschistiakow, 151

Vahlen, 133, 158 (157)

Vdlyi, 150

Van der Corput, 139

Von Ettingshausen, 115 (121)

Von Schrutka, 158

Von Sterneck, 151 (153)

Walla, 126

Weber, 123, 133, 150

Wevr, 151

Wolfskehl, 134 (132, 138)

Zerr, 140

Zsigmondy, 132, 152 (145,
146, 155)

Ch. VI. Periodic Decimal Fractions; Factors of 10"±1

Adams, 179
Akerlund, 176
Albanna, 159
Anonymous, 163
Arndt, 179

Bachmann, 174, 176
Barillari, (167)
Beaujeux, 167 (171)
Bella\-itis, 170
Bennett, 177

Bernoulli 160 (159, 161, 166)
Bertram, 165 (168)
Bettini, 175

Bickmore, 175 (176, 179)
Biddle, 176
Bork, 174 (165)
Bouniakowsky, 171
Bredow, 163

Brocard, 165, 172, 174 <159)
Broda, 169, 172
Brogtrop, 170

Burckhardt, 161 (168, 172,
173, 177)

Carra de Vaux, 159
Catalan, 164
Cicioni, 177
Clarke, 160
Collins, 166
Contejean, 173
Cullen, 176 (179)
Cunningham, 168, 175-177,

179 (161, 165, 169, 172,

174)

De Coninck, 168
Desmarest, 165 (168, 170,

177)
Dickson, 174
Dienger, 179
Druckenmiiller, 163

El-M&ridini, 159
Escott, 176
Eulor, 160 (165)

Farey, 162
Felkel, 161

Filippov, 177, 179
Fujimaki, 176

Gauss, 161 (167, 170)

Genese, 173

Genocchi, 165 (160)

G^rardin, 177 (161, 165)

Ghezzi, 178

Glaisher, 162, 166, 168, 170,

171 (173, 175)
Goodwyn, 161, 162 (170)
Gosset, 177

Hartmarm, 168
Hausted, 170
Heal, 173
Heime, 166

Hertzer, 176, 177 (165)
Hoppe, 179
Howarth, 179
Hudson, 166 (167)

Ibn-el-Banna, 159

Jackson, 177
Jenkins, 179
Johnson, 172

Kessler, 172, 174 (161, 176)
Kraitchik, 179
Kraus, 174
Kronecker, 176

Lafitte, 164
Lagrange, 179
Laisant, 167, 171, 173
Lambert, 159 (160, 168)

[161]
Law, 161
Lawrence, 175
Lebesgue, 167
Lehmann, 167
Leibniz, 159
LeLasseur, 172
Leman, 179
Levanen, 179
Lichtenecker, 178
Lionnet, 167
Loof, 165, 171, 172, 175 (168)

Lucas, 159, 171, 172, 175, 177

(176)
Lugh, 172

Mahnke, 159
Maillet, 178
Mansion, 169
Maver, 173, 174
Mever, 167 (176)
Midy, 163 (164, 166)
Mignosi, 177
Miller, 176
Morck, 179
Morel, 167
Moret-Blanc, 168
Muir, 168, 169
Murer, 175

Nordlund, 176

Oberreit, 161
OUver, 166

Pasternak, 178
PeUet, 167
Perkins, 163 (176)
Pokorny, 166
Poselger, 162
Prouhet, 164

Reuschle, 165, 169 (172, 174,

176)
Reyer, 165
Rej-nolds, 175
Rieke, 173
Robertson, 159 (160)

Sachs, 175
Sahnon, 168
Sanio, 167
Sardi, 167 (175)
Schlomilch, 171 (172)
Schroder, 168
Schroter, 161
Schuh, 177
Seelhoff, 160
Sensenig, 169

Shanks, 168, 170 (161, 165,
169, 176)

Author Index

473

Sornin, 164
Stammer, 166
Stasi, 178
Sturm, 166
Suffield, 166

Tagiuri, 176

Telosius, 179
Thibault, 164 (168)

Van den Broeck, 172
Van Henekeler, 165

WaUis, 159 (160)
Weixer, 179

Welsch, 179
Wertheim, 161
Westerberg, 163
Wiley, 179
Workman, 176 (168)
Wucherer, 161
Young, 165

Ch. VII. Primitive Roots, Binomial Congruences.

Alagna, 217 (218)

Alasia, 190 (210)

AUegret, 190

Amici, 197, 216, 217

Anonymous, 204

Arndt, 187, 188, 208, 209

(193)
Arnoux, 199, 218

Bachmann, 194, 199, 218

Barillari, 192 (193)

Barinaga, 203

Bellavitis, 193

Bennett, 195

Berger, 214 (215)

Besant, 217

Bhdscara, 204

Bindoni, 199

Bougaief, 213

Bouniakowsky, 191, 192, 212

(204)
Brennecke, (208)
Bukaty, 212 (210)
Burckhardt, (185, 201)
Buttel, 190

Cahen, 198
Calvitti, (204)
Carmichael, 200, 202
Cauchy, 184, 186, 187, 209

(188, 190, 194, 195, 198,

200, 212, 213)
Cayley, 191
Chabanel, 202
Christie, 199
CipoUa, 200, 218-221
Colebrooke, [204]
Concina, 222
Contejean, 194
Creak, 222
Crelle, 185, 209 (186, 188,

190, 208)
Cunningham, 198-204, 217-

222 (185, 189, 190, 213)

Daniels, 194
Da Silva, 190, 210
De Jonquieres, 197
Demeczky, 201

Desmarest, 188, 189, 210

(214)
Dickstein, 210, 215
Dirichlet, 185, 191, 211 (198,

214)
Dittmar, 212
Dupain, 192

Epstein, 200

Erlerus, 186, 208 (196)

Euler, 181, 204, 205 (222)

Foghni, 199
Fontene, 201
Forsyth, 193
Frattini, 193
Fregier, 183
Friedmann, 219
Frolov, 196

Gauss, 182, 194, 195, 207
(183-185, 187, 188, 193.
194, 197, 198, 209, 210, 213,
214)

Gazzaniga, 213

Gegenbauer, 194, 196, 215

G6rardin, 222

Goldberg, 192

Gorgas, 211

Grave, 201

Grigoriev, 199

Grosschmid, 221

Hacken, 194
Hanegraeff, 210
Heime, 191
Hill, 192
Hofmann, 193
Houel, 191
Hurwitz, (203)

Ivory, 184 (190)

Jacobi, 185 (188, 190-192,

198, 201, 203, 211)
Japanese, 204

Keferstein, 194
Korkine, 201 (203, 221)

Kraitchik, 202
Krediet, 203
Kronecker, 192, 198
KuUk, 189
Kunerth, 213

Lacroix, 183 [208]

Ladrasch, 212

Lagrange, 181, 205 (182, 206,

207, 214, 216)
Laisant, 193
Lambert, 181
Landau, 201
Landry, 190
Laplace, 208
Lazzarini, (222)
Lebesgue, 184, 188-192, 208,

211 (196, 204)
Legendre, 182, 205-207 (185,

187, 188, 194, 208, 213-

215, 219, 222)
Leibniz, 215
Libri, 208
Lucas, 194, 213 (198, 200,

202, 203, 218)

Maillet, 202
Mann, 215
Marcolongo, 214
Maser, [182, 206, 207]
Massarini, 188
Mathews, 195, 215
Matsunaga, 204
Maximoff, 222
Mayer, 216
Meissner, 219
Mertens, 198 (192)
Meyer, 211
Miller, 198, 201, 203
Minding, 185
Moreau, 198
Murphy, 186

Nordlund, 200

Oltramare, 189, 190 (191)
Ostrogradsky, 185 (186, 188)

Pepin, 197, 213

474

Author Index

Perott, 194, 196, 197

Picou, 218

Pocklington, 222

Poinsot, 183, 184, 187, 208,

209 (190, 194, 199, 207,

208)
Posse, 201, 202, 203, 221
Prouhet, 188 (194, 208)

Rados, 222

Reuschle, 190, 213 (200, 204)
Richelot, 185 (194)
Rochette, 188

Sancery, 193, 213 (194, 195)
Schapira, 188

Scheffler, 190, 194

Schering, (208)

Schuh, 202 (221)

Schumacher, 202

Schwartz, 194

Seelhoff, 214

Serret, 194, 214

Smith, 191, 210 (184, 190,

207)
Speckmann, 216, 217
Stankewitsch, 213
Stasi, 221
Stern, 184, 208 (187, 194, 199,

203)
Studni6ka, 215
Szily, 194

Tamarkine, 219
Tchebychef, 188 (185, 191,

195, 196, 198, 207)
Thiele, 212

Tonelli, 215, 216 (217, 218)
Traub, 192

Vab-off, 222

Von Schrutka, 202, 221

Wcrtheim, 194, 196, 197, 199,

214 (201, 202)
Woodall, 203 (202)
Wronski, 210 (211, 212, 215,

218)

Abel, 259

Alasia, 224

Amoux, 250, 251, 254 (255)

Bachmann, 250, 251
Bauer, 249, 251
Bellavitis, 244
Biase, 260

Borel and Drach, 247
Bunickij, 260
Bunitzky, 260
Bussey, 251

Cailler, 255, 256

Carey, 249

Cauchy, 223, 225, 238, 252,

258 (243)
Ch&telet, 262
Christie, 262
Cipolla, 232
Cordone, 247, 254, 259
Creak, 262
CreUe, 223 (224)
Cunningham, 262

Damm, 247, 254

Da Silva, 224

Dedekind, 240, 245 (242)

Demeczky, 228

Dickson, 232, 248-250, 252,

254, 256 (244, 249)
Dina, 246

Earnshaw, 223
Eisenstein, 239
Epstoen, 250 (249)
Escott, 256
Euler, 223 (259)

Fermat, 257 (260)
Frattini, 259, 261

Galois, 235 (232, 239, 242,
243, 247, 252)

Zsigmondy, 195, 197, 216

Ch. VIII. Higher Congbuences.

Neikirk, 251
Oltramare, 253 (254)

Gauss, 223, 233 (235, 238,

240, 256)
Gegenbauer, 226-229, 231
Genocchi, 258
Giudice, (259)
Grotzsch, 261
Grunert, 224
Guldberg, 248, 250

Hathaway, 259

Hayashi, 256

Hensel, 226, 249

Hermite, 225

Hurwitz, 231, 259 (232, 233)

Iwanow, 254

Jacobi, 235

Jenkins, 259

Jordan, 243, 244, 261 (252)

Kantor, 255, 262

Konig, 225 (226, 229)

Krediet, 261

Kronecker, 226, 249, 260

(228, 229, 251)
Kiihne, 232

Lagrange, 223

Landau, 261

Lebesgue, 224, 235, 258 (245)

Legendre, 223, 257

Lerch, (227, 228)

Le Vavasseur, 248

Libri, 224 (225, 258)

Lipschitz, 260 (257)

Maser, [223, 233, 235]
Mathieu, 241 (248)
Miller, 251
Mirimanoff, 255
Mitchell, 246
Moore, 247

Pellet, 243, 245, 246
Pepin, 244
PiccioU, 261
Pierce, 262
Poinsot, 224 (259)

Rados, 226, 233, 261, 262

(225)
Raussnitz, 226

Sanderson,^252
Satunovskij, 231
Scarpis, 252
Schonemann, 225, 236, 238,

239 (251)
Schiitz, 243
Schwacha, 233
Serret, 239, 241, 244, 258

(233, 245, 246, 248, 256)
Smith, 241, 259
Snopek, 229
Stephan, 232
Stickelberger, 249 (251)
Sylvester, 259 (245)

Tarry, 252
Tchebychef, 225
Tihanyi, 262

VonSterneck, 255, 260, 261

(262)
Voronoi, 251, 253 (255)

Weber, 247
Wertheim, 260
WoodaU, 262
Woronoj, 253, 254
Wronski, 257

Zsigmondy, 230, 247

Author Index

475

Ch. IX. Divisibility of Factorials, Multinomial Coefficients.

Adams, 278
Andr6, 263, 265-6
Anonymous, 275
Anton, 263, 271
Arlvalo, 278
Arndt, 276 (277)

Babbage, 270
Bachmann, 266, 274
Bauer, 268
Beaujeux, 277
Beeger, 278
Bernoulli (268)
Bertram, 263
Birkeland, 269
Bouniakowsky, 276-7
Bourguet, 266

Carmichael, 264, 276, 278
Catalan, 265-7, 271-2
Cauchy, 265
Cayley, 269, 270
Cesltro, 266, 272
Child, 278
Cunningham, 265, 274

De Brun, 263
De Jonquieres, 270
De Polignac, 266, 269
De Presle, 267
Dickson, 273 (272)
Dirichlet, 275 (276)

ElUott, 270

Fleck, 274-5
Fonten6, 274
Franel, 276

Gauss, 269

Gegenbauer, 267, 272
Genocchi, 271
Genty, 263

Gerhardt, [269]
Glaisher, 268, 273-4
Gmeiner, 267
Greatheed, 269
Grosschmid, 274
Guerin, 275

Hayashi, 274
Heine, 267
Hensel, 263

Hermite, 266, 271-2 (267,
269, 274)

Jacobi, 275 (276)
Janichen, 265
Jenkins, 269, 271

Kapferer, 274
Kempner, 263
Korkine, 276
KJronecker, 276
Kummer, 270 (272-3)

Lagrange, 275
Laisant, 277
Landau, 267-9
Lebesgue, 269
Legendre, 263 (264)
Leibniz, 269 (270)
Lerch, 276
Libri, 270
Li^nard, 266
Lionnet, 269
Liouville, 276

Lucas, 266, 271-2, 275 (274,
278)

MacMahon, 268
MaiUet, 265, 268
Maitra, 269
Malo, 276

Marks, 278
Mason, 278

Mathews, 272-3
Mertens, 273
MUler, 269
Morley, 273

Neuberg, 263, 266
Nielsen, 274, 278

Oltramare, 277
Ouspensky, 276

Pascal, 269
Pessuti, 269
Petersen, 272
Pincherle, 267

Ram, 274
Rogel, 267, 272

Schlomilch, 272
Schonbaum, 269
Schonemann, 265
Segar, 269 (270)
Sharp, 272
Stern, 270
Stickelberger, 263
Stridsberg, 264, 269
Studnicka, 270
Szego, 265
Szily, 273

Tanner, 267
Teixeira, 267, 277
Thue, 267

Van den Broeck, 272
Vandiver, 276
Vecchi, 277

Waring, 275
WeiU, 266 (267-8)
Wolstenhohne, 271-2 (275)
WoodaU, 272

Ch. X. Sum and Number of Divisors.

Ahlborn, 291
Andreievsky, 288

Bachmann, 279, 315, 321,

323 (281, 291, 319)
BeU, 323, 325
Berger, 291, 312, 317 (292,

295 299)
Bougaief, 303, 315 (301, 312,

316, 325)
Bouniakowsky, 283, 284, 287

(281, 286, 302)

Burhenne, 283

Busche, 306, 308, 314, 319
(315, 323)

Cantor, 291

Catalan, 289-291, 302, 306

(292, 295)
Ces^ro, 290-4, 302, 306, 308

(295, 298-9, 312, 315,

320)
Cunningham, 325

De Vries, 317

Dirichlet, 281-2, 301 (284r-5,
289, 291, 298-9, 305, 307,
314-5, 318, 322, 325)

Egorov, 312
Elliott, (318)

Euler, 279 (284, 290, 303,
312, 317-8, 321, 323)

Fekete, 321
Fergola, (302)
Franel, 317-8

476

Author Index

Gauss, 308

Gegenbauer, 298-9, 301-5,

307-8, 316 (288, 315, 318,

325)
Giulini, 319
Glaisher, 289-292, 294-6,

300, 303-4, 308-310, 312,

318, 320, 322 (280, 302,

321)
Gram, 295, 308 (291)
Gronwall, 322

Hacks, 306-7 (303, 322)
Halphen, 289, 290 (294-5,

309, 312)
Hammond, 311 (325)
Hansen, 319
Hardy, 325 (319)
Hemming, 284
Hermite, 292, 295, 297, 306

(304-5, 315)

Jacobi, 281-2 (283, 288, 290,
295. 300-1, 313, 317-8)

Knopp, 321, 323
Kronecker, 297, 318

Laisant, 308

Lambert, 280 (306, 323)
Landau, 294, 305, 317-8,

321-4
Lebesgue, 284
Legendre, 281
Lerch, 307, 313, 316 (314-5,

317)
Lionnet, 288
LiouviUe, 284-8 (291-4, 298-

9, 312-3, 321, 323)
Lipschitz, 291-2, 298, 302

(299, 307, 313, 315)
Lucas, 291, 312

Meissel, 284 (299, 314, 317-

8, 322)
Meissner, 320
Mellin, 319

Mertens, 289 (294, 315)
Minetola, 322
Minin, 313
Mobius, 296

Nachtikal, 316

Pexider, 320
Pfeiffer, 305 (322)
PUtz, 291 (317, 322, 325)
Plana, (281)

Radicke, 291
Ramanujan, 323-5
Roberts, 303
Rogel, 316, 325
Runge, 302

Sardi, 288

Schroder, 314, 319, 321 (315)

Sierpinski, 320

Smith, 289 (296)

Sokolov, 312

Steffensen, 323

Stern, 281, 303 (321)

Stieltjes, 292

Strnad, 307

Traub, 287

Vahlen, 313
Van der Corput, 323-4
Von Mangoldt, 294
Von Sterneck, 317
Voronoi, 318-9 (322, 325)

Waring, 280 (303)
Wigert, 320, 323, 325

ZeUer, 291, 295, 313 (299,
303, 312, 321)

Ch. XI. Miscellaneous Theorems on Divisibility, Greatest Common
Divisor, Least Common Multiple.

Anonymous, 327
Avery, 332
Axer, 331

Bachmann, 335
Barinaga, 336
Berger, 328
Binet, (332)
Birkeland, 331
Borel, 334 (333)
Bougaief, 327 (328, 330)
Bouniakowsky, 332
Brown, 336

Ces^o, 328, 333 (336)

Darbi, 335

Dedekind, 334

De Jough, 335

De la Valine Poussin, 330

(331)
De Polignac, 336
Dickson, 331
Dienger, 327
Dintzl, 335

Dirichlet, 327, 335 (328-331)
Dupr^, (332)

Gegenbauer, 328-330, 333,

336
Gelin, 335
Grolous, 328
Guzel, 331

Hacks, 330, 333
Hammond, 333
Hensel, 334 (333)

Klein, 334
Kluyver, 335
Kronecker, 334 (336)

Lam6, (332)
Landau, 328, 331
Lebesgue, 332 (335)
Lecat, 336
Lucas, 333

Mertens, 334-5
Mitchell, 336
Moschietti, 332

Neuberg, 333

Pichler, 335

Rogel, 331
Ross, 336
Rothe, 332

Saint-Loup, 330

Sierpinski, 335

Stern, 335

Stieltjes, 333

Stifel, 327

Sylvester, 327, 333, 336

Terquem, [327]

Van der Corput, 332
Vandiver, 331
Verhagen, 336
Verson, 332

Weitbrecht, 332
Wijthoff, 336
WUlaert, 336

Yanney, 335

Zeller, 328

Author Index

477

^■Alkarkhi, 337
HpAnonymous, 339, 344
K Anton, 345
^ Apianus, 337

Argardh, 338

Avicenna, 337

Ayza, 346

Badoureau, 345
Barlow, (346)
Belohldvek, 342
Biase, 343
Biddle, 345
Bindoni, 343
Borgen, 342
Bougaief, 340 (342)
Bougon, 341
Bouniakowsky, 344
Breton, 341
Broda, 345
Brooks, 345
Bruzzone, 344
Burgess, 345
Battel, 344

Calvitti, 345
Cantor, [337]
Carra de Vaux, 337
Castelvetri, 338
Catalan, 340
Cattaneo, 346
Cazes, 345
Cesaro, 345
Chiari, 344
Christie, 341, 345
Chuquet, 337
Church, 345
Cicero, 346
Collins, 345
Conti, 345
Crelle, 339
Csada, 346
Cunningham, 345

D'Alembert, 338 (344)
Da Ponte Horta, 345
De Fontenelle, 338
De Lapparent, 344
Delboeuf , 340
De Montferrier, 344
Dickstein, 341, 345
Dietrichkeit, 341
Dietz, 344
Dodgson, 342
Dorr, 345
Dorsten, 345

Ch. XII. Criteria for Divisibility by a Given Number.

Dostor, 340
Drach, 345
Dupain, 339

Elefanti, 344
EUiott, 339
Evans, 345

Fazio, 345
Filippov, 346
Flohr, 344
Folie, 339
Fontebasso, 346
Fontes, 341-2 (337)
Forcadel, 337

Gale, 346
GeUn, 343, 345
Gerardin, 345
Gergonne, 338 (345)
Ghezzi, 345
Gorini, 344
Greenfield, 345
Greenstreet, 345
Grunert, 344

Haas, 345
Harmuth, (346)
Heal, 342
Heilmann, 341
Herter, 338 (344)
Hill, 338
Hippolytos, 337
Hocevar, 340
Holten, 340
Hommel, 340

Ibn Albanna, 337

Ibn Mtisa Alchwarizmi, 337

Ibn Sina, 337

Ingleby, 345

lodi, 346

Jenkins, 345
Jorcke, 345
Joubin, 346

Karwowski, 344
Kraft, 338
Krahl, 346
Kroupa, 346
Kylla, 346

Lagrange, 338
Lalbaletrier, 345
La Marca, 346
Lange, 345

La Paglia, 346
Lebesgue, 344
Lebon, (346)
Lenth6ric, 346
Lenzi, 345

Leonardo Pisano, 337
Levanen, 341
Lichtenecker, 346
Liljevalch, 338 (340)
Lindman, 344
Loir, 341-2, 345
Loria, 343
Lubin, 345

Malengreau, 343
Mantel, 340
Mariantoni, 345
Marre, [337]
Mason, 344
Meissner, 343
Mennesson, 345
MiceU, 346
MoUer, 340
Morale, 345-6

Nannei, 344
Nasso, 345
Niegemann, 339, 344
Niewenglowski, 345
Noel, 341

Oskamp, 340
Otto, 340

Paciuolo, 337

Paoletti, 346

Pascal, 337 (338, 342j 344-5)

Perisco, 346

Perrin, 341

Pick, 345

Pietzker, 345

Pinaud, 344

Plakhowo, 342

Polpi, 346

Recorde, 337
Reyer, 344
Riess, 342
Ripert, 343
Romm, [337]

Sanvitali, 338
Schlegel, 340 (345)
Schobbens, 341
Schroder, 346
Schuh, 344
Sibt el-MAridini, 337
Speckmann, 345

478

Author Index

StoufF, 345
Stujrvaert, 344
Sylvester, 342
Szenic, 345

Tagiuri, 343
Tarry, (346)
Terquem, 344
Tiberi, 346
TirelU, 346

Transon, 339
Tucker, 341

Unferdinger, 345

Valerio, 342
Van Langeraad, 344
Vincenot, 344
Volterrani, 346

Walenn, 345
Wertheim, 345
Widmann, 337
Wilbraham, 339
Wronski, 344

Young, 344

Zbikowski, 339
Zeipel, 339
Zuccagni, 345

Ch. XIII. Factor Tables, Lists of Primes.

Akerlund, 355
Alliston, 356
Anjema, 348
Aratus, 347
Aubry, 355

Barlow, 351 (355)
Beguelin, 349
Bernhardy, 347
Bernoulli, 349 [350]
Berteken, 354
Bertrand, 349
Boethius, 347
Boulogne, 356
Bouniakowsky, 353
Bourgerel, 354
Brancker, 347 (348, 350)
Burckhardt, 350 (352-5)

Camerarius, 347
Cataldi, 347
Cayley, 353
Chernac, 350 (351)
Colombier, 351
CreUe, 351-2

Cunningham, 354-5 (350-2,
356)

D'Alembert, 349

Dase, 352 (353-5)

Davis, 352

De Polignac, (356)

Deschamps, 355

Desfaviaae, 350

De Traytorens, 348 (350)

Di Girio, 354

Dines, 355

Dodson, 348

Du Tour, 348

Eratosthenes, 347 (348, 353-

6)
Escott, 355 (356)
Euler, 349 (356)

Felkel, 349, 350

Gauss, 350, 352 (356)
G6rardin, 356
Gill, 353

Glaisher, 350, 353 (355)
Goldberg, 352
Gram, 354
Groscurth, 353
Griison, 350
Gudila-Godlewski, 353
Guyot, 351

Hansen, 356
Hantschl, 351
Harris, 348
Hindenburg, 349
Hinkley, 351 (347)
Horsley, 347
Houel, 351-2
Hiilsse, [350]
Hutton, 351

Ibn Albannd, 347

Jager, 348
Johnson, 353
Jolivald, 354

Kastner, 350
Kempner, (356)
Kliigel, 348
Kohler, 351
Krause, 350
Kronecker, (354)
Kriiger, 348
KuUk, 351 (355-6)

Laisant, 354-5
Lambert, 348, 350 (349)
Landry, 351
Lebesgue, 352
Lebon, 355-6
Lehmer, 352-3, 355-6
Leonardo Pisano, 347
Libri, 347
Lidonne, 350

Lionnet, 355
Lucas, 353

Marci, 349
Marre, [347]
Maseres, 350
Meissel, 352 (350)
MerUn, (356)
Mobius, 351
Morehead, 355

Neumann, 350
Nicomachus, 347
Noviomagus, (356)

Oakes, 352
Oberreit, 349
Ozanam, 349

FeU, [347]
Perott, 352
Petzval, 352
Pigri, 348
Poetius, 348
Poretzky, (356)

Rahn (Rhonius), 347
Rallier des Ourmes, 348
Rees, 351
Reymond, (356)
Rosenberg, 352 (355)
Rosenthal, 349

Saint-Loup, 353 (356)
Salomon, 351
Schaffgotsch, 349
Schallen, 351
Schapira, 354
Schenmarck, 350
Schwenter, 348
Seelhoff, 353
Simony, 353 (354)
SneU, 350
Speckmann, 354
Stager, 356
Struve, 350
Suchanek, 354

Author Index

479

Tarry, 355
Tennant, 354
Tessanek, 349
Tuxen, 353

Valerio, 354

Van Schooten, 347
Vega, 350
VoUprecht, 353^
Von Stamford, 349
Von Sterneck, 354

Wallis, 348 (347)
Wertheim, [347]
WilUgs (Willich), 348
Wolf, 348
WoodaU, 354 (356)

Ch. XIV. Methods of Factoring.

Aubry, 373 (369)

Ball, 368

Barbette, 367, 373
Bartl, 370
Beguelin, 361, 366
Bernoulli, 371
Bickmore, 369
Biddle, 359, 367, 369-374
Birch, 368
Bisman, 374

Bouniakowsky, 369 (370)
Burgwedel, 365
Busk, 358 (359)

Cahen, 364
Canterzani, 366
Cantor, [366]
Christie, 361, 367, 372
Cole, 365
Collins, 357
Cullen, 365, 369
Cunningham, 358-9, 361,
365, 368-9, 373-4 (362)

De Bessy (see Frenicle)
De Montferrier, 358
Deschamps, 367
Dickson, 370 (360)

Euler, 360-2 (363-5)

Fermat, 357 (358, 367)
Frenicle, 360
Fuss, 362

Gauss, 363, 369 (364-5, 370)
GIrardin, 365-7, 370, 374

Gmeiner, 374
Gough, 371
Grube, 363

Hansen, (371)
Harmuth, 361
Henry, 358
Hudson, 358

Johnsen, 369
Joubin, 372

Kausler, 357, 362
Kempner, 374
Kielsen, 372
Klugel, 366
Kraft, 370
&aitchik, 359, 360
KuUk, 361, 372

Lagrange, 369
Lambert, 371
Landry, 358, 369, 371
Laparewicz, 365
Lawrence, 358-360
Lebon, 359, 373
Legendre, 361-2 (363)
Lehmer, 368
Levanen, 364
Lucas, 363-4 (372)

Marcker, 368

Mathews, 364

Matsunaga, 371

Meissner, 372 (358, 364, 367)

Mersenne, 357, 360 (367-8)

Meyer, 365

Minding, 363

Mobius, (374)

Neimaann, 359
Niegemann, 366
Nordlund, 370-1 (369)

Pepin, 364
Petersen, 360
Pockhngton, 370

Rawson, 367
Reymond, 374

Schaffgotsch, 367
Schatunovsky, 370
Seelhoff, 363 (365)
SeUwanoff, 364
Speckmann, 367
Studnicka, 366

Tchebychef, 363
Teilhet, 359
Tessanek, 366
Thaarup, 358
Thiehnann, 368

Vaes, 359, 360
Vah-off, 365
Von Segner, 366
Vuibert, 361

Waring, 362
Warner, 358
Weber, 364
Wertheim, 358, 361
Winter, 372
WoodaU, 369

Ch. XV. Fermat Numbers Fn = 22^^-1-1.

Anonjmaous, 376
Archibald, 380

Bachmann, 379
Ball, 378
Baltzer, 375
Beguelin, 375 (377)
Bisman, 379
Broda, 377

Canterzani, 375

Carmichael, 377, 380
Catalan, 377
Cipolla, 378
Cullen, 378
Cunningham, 378-380

Eisentein, 376
Euler, 375

Fermat, 375 (376)
Frenicle, 375

Gauss, 375
Gelin, 377
Genocchi, 375
G^rardin, 377, 380
Goldbach, 375
Gosset, 379

Hadamard, 378
Henry, 375, 380
Hermes, 378
Hurwitz, 378 (380)

480

Author Index

Joubin, 376

Klein, 378 (379)
Klugel, 375

Landry, 376-7
Legendre, (378)
Le Lasseur, 377
Lipschitz, 378
Lucas, 376-8 (379)

Malvy, 378 (376)
Mansion, 375
Mersenne, 375
Morehead, 376, 379

Nazarevsky, 378

Pepin, 376 (377-380)
Perv'ouchine, 376-8
Pervusln, 376

Proth, 377 (378)

Scheffler, 378
Seelhoff, 377
Simerka, 377
Studnidka, 377

Western, 378-9
Woodall, 379

Ch. XVI. Factors of a"±b".

AurifeuiUe, 383 (386)

Bang, 385 (386)
Bauer, 385
Beguelin, 381 (385)
Bickmore, 386 (385)
Biddle, 387 (391)
Birkhoff, 388 (386)

Carmichael, 389, 390 (388)
Catalan, 383-4 (386)
Cunningham, 386-391 (384)

Dedekind, 384
Dickson, 388-9
Dines, (391)
Dirichlet, (391)

Escott, 385, 387-9
Euler, 381-2 (383, 388,
390-1)

Fauquembergue, 390
Felkel, 382
Fermat, 381
Fontene, 390
Foster, 385

Gauss, 382
Genese, 385
Gt5rardin, 390
Germain, 382 (383)
Gianni, 385
Glaisher, 386, 388

Henry, 382

Kannan, 389
Kraitchik, (391)
Kronecker, 385, 387
Kummer, 383

Lawrence, (391)

Lebesgue, 382-3

Lef^bure, 384

Legendre, 382

Le Lasseur, 383 (384-5, 389)

Lucas, 383^, 386

Markoff, 386
Minding, 382
Miot, 389
Morehead, (391)

Pepin, 384-6
Plana, 383
Pocklington, 390

Realis, 384
Reuschle, 382-3

Sanjana, 389
Scheffler, 385
Schering, 382
Seelhoff, (391)
Soons, 383
Sylvester, 384-5

Tchebychef, 382
Teilhet, 388

Vah-off, 390

Van der Corput, 390

Vandiver, 387-8

Welsch, 389
Wertheim, 388
WoodaU, 386, 388, 391
Workman, 386

Zsigmondy, 386 (388)

Ch. XVII. Recurring Series; Lucas' u„, v„.

Agronomof, 406
Amsler, 410
Andr6, 408
Archibald, 411
Arista, 405
Arndt, (397)
Aubry, 405

Bachmann, 394, 405
Bastien, 406
Bernoulli, 407 (408)
Betti, 408
Bickmore, 404
Binet, 394 (403)
Boutin, 406

Braun, 411
Brocard, 402

Candido, 405
Cantor, [407]
Carmichael, 394, 406 (398,

400)
Cassini, 407

Catalan, 395, 402-3 (404)
Ces^ro, 401-2
Christie, 404
CipoUa, 405
Cunningham, 397

Damm, 405

Degen, 407, 411
De Longchamps, 401, 408
De Moivre, 407
Dickson, 405, 410
Dienger, 394
Dirichlet, 393 (402)
D'Ocagne, 402, 409, 410

Emmerich, 404

Escott, 404-5

Euler, 393, 407 (397-8, 400)

Fermat, (396)
Fibonacci (see Leonardo)
Fontte, 403

Author Index

481

Foster, 403
Fourier, 408
Fransen, 405
Frisiani, 408
Frolov, 403

Galois, (403)

Gauss, 393 (397)

Gegenbauer, 403, 409

Gelin, 401

Genocchi, 394, 397, 402 (405)

G^rardin, 406

Girard, 393

Grosschmid, 394

Hayashi, 410
HiU, 394

Kepler, (411)
Kronecker, 402 (393)

Lagrange, 393, 407 (396-7,

408)
Laisant, 408, 410
LamI, 394
Landau, 404r-5
Laparewicz, 405
Laplace, 407
Lattes, 410
Legendre, 393
Le Lasseur, 400
Leonardo Pisano, 393 (394r-

411)

Liebetruth, 402

Lionnet, 394

Lucas, 394-403 (405-6)

Magnon, 402
Maillet, 403, 410
Malfatti, 407
Malo, 404, 406
Mantel, 403
Mathieu, 405
Mersenne, (397)
Moret-Blanc, 397
Murphy, 408

Netto, 410
Neuberg, 410
Nicita, 411
Niewiadomski, 406

PaoU, 407
PeUet, 406
Pepin, 398, 401
Perrin, 404, 410
Piccioli, 407
Pierce, 407
Pincherle, 409
Prompt, 406
Proth, (398)

Ranum, 410
R6aUs, 404

Riccati, 407
Ruggieri, 405

Sancery, (397)
Scheibner, 408
Scherk, 411
Schlegel, 411
Schonflies, 403
Seliwanov, 403
Serret, 394
Siebeck, 394 '
Simson, 393
Stirling, 407
Study, 409
Svanberg, 411
Sylvester, 401, 403, 411

Tagiuri, 404
Tarn, 411
Traverso, 410

Valroff, 405

V^sz, 411

Vogt, 411

Von Sterneck, (398)

Wasteels, 405
Weiss, 411
White, 405
Whitworth, 411

Zeuthen, 405

Ch. XVIII. Theory of Prime Numbers.

Andreoli, 434
Aubry, 422
Auric, 414

Bachmann, 416, 418, 432

Bang, 418-9

Baranowski, 432

Barinaga, 428, 438

Bauer, 419, 420

Berton, 416

Bertrand, 435 (413, 425, 436)

Bervi, 419

Biddle, (426)

Bindoni, 427

Birkhoflf, 418

Boije af Gennas, 414

Bonolis, 436

Bougaief, 422, 429 (430-1)

Bouniakowsky, 421

Braun, 414, 421, 437

Brocard, 425-6, 436

Brun, 438

Cahen, 414, 419, 436

Cantor, 422, 425
Carmichael, 420, 428
Catalan, 421, 429, 431, 435

(426)
Cesaro, 430 (432, 435)
Chabert, 420
Chiari, 428
CipoUa, (426)
Coblyn, 438
Cole, (426)

Cunningham, 417, 423
Curjel, 429, 431-2

Dedekind, 415

De Jonqui^res, 429 (432)

De la Vallee Poussin, 416,

418, 439-440 (417)
De Monddsir, 430
De Montferrier, 426
DePohgnac, A., 424, 439

(425)
De Pohgnac, C, 436-7
De Rocquigny, 425
Desboves, 415, 422, 435 (436)

Descartes, 421

Deschamps, 439

Devignot, 426

Dickson, 417

Dirichlet, 415, 417 (416, 418)

Dormoy, 437

Dupr6, 415

Durand, 415

Enestrom, [421]
Eratosthenes, (424)
Escott, 420, 426, 428
EucUd, 413

Euler, 413, 415, 420-1, 424,
426

Fontebasso, 427
Frobenius, 421

Gambioli, 427

Gauss, 438

Gegenbauer, 413, 427, 431-3

(426, 435)
Genocchi, 418

482

Author Index

Genty, (426)
Giovannelli, 424
Goldbach, 420-1, 424
Graefe, 432
Gram, 430
Guibert, 425

Hacks, 414, 427
Hadamard, 424, 439, 440
Hammond, 423, 429, 438
Hardy, 438, 440
Hargreave, 429
Haussner, 422 (423)
Hayashi, 433
Heiberg, [413]
Heine, 415
Hensel, 416, 418-9
Hermite, 437
Hoffmann, 430
Hossfeld, 431
Hurwitz, (426)

Isenkrahe, 437
Iwanow, 419, 437

Jaensch, 413
Johnsen, 429
Jolivald, 427 (426)

Klein, 438

Kossler, 435

Kraft, 426

Kraus, 418

Kronecker, 413, 416, 418,

425, 429 (414)
Kummer, 413

Labey, [413]
Lagrange, 424-5 (426)
Lambert, (426)
Landau, 417-9, 423,

43.5-8, 440
Landry, 418
Laurent, 427 (433)
Lebesgue, 418-9 (426)
Lef^bure, 418

425,

Legendre, 415, 420, 429, (416,

430-1, 434-5)
Leibniz, (426)
Le Lasseur, 420
Lemaire, 420, 426
Lemoine, 424
Le Vavasseur, 437
Levi-Civita, 433
L<5vy, 414, 421

Lionnet, 422, 426, 429 (423)
Lipschitz, 429 (432)
Littlewood, 440
Lorenz, 430

Lucas, 418-9, 421 (426, 428)
LugU, 431

MaiUet, 423, 425, 436
Marcker, 436
Markow, 437
Martin, 426
Mathews, 429
Mathieu, 425
Meissel, 429, 431 (432)
Meissner, 427, 438
Merlin, 424
Mertens 416-8
M6trod, 415
Meyer, 418
Minetola, 427, 434
Minin, 433
Miot, 421
Moreau, 416

Oltramare, 420
Oppermann, 435

Paci, 430
Pascal, 420
Perott, 413-4
Petrovitch, 434
Pexider, 433
Piltz, 416

Pocklington, 419, 428
Proth, 435

Rados, 428
Riemann, 439

Ripert, 423, 425
Rogel, 429, 431, 433-4

Sardi, (426)

Schaffgotsch, (426)

Scheffler, 416, 431

Schepp, [420]

Schering, 418

Scherk, 436

Schur, 419

Serret, 418-9, 435

Smith, 436, 439

Speckmann, 416

Stackel, 423 (422)

Stasi, 428

Stern, 424, 426

Stieltjes, 414, 436

Stormer, 437 (414)

Studni6ka, 423

Sylvester, 416, 418-9, 422-3,

429, 431-2, 435, 437, 439

(433)

Tchebychef, 413, 435, 437,

439 (426)
Teege, 417
Terquem, 421, 436
Thue, 414
Torelli, 440

Vahlen, 419

Van der Corput, 419

Vandiver, 418

Van Laar, 431

Vecchi, 424, 428

Von Koch, 427, 432 (433)

Von Sterneck, 419, 427, 435

Warmg, 421, 425
Weber, 417-8
Wendt, 418
Wertheim, 429
Wigert, 432 (428, 434)

Zignago, 416
Zondadari, 428
Zsigmondy, 418, 427 (426)

Ch. XIX. Inversion of Functions; Mobius' Function n{n); Numerical

Integrals and Derivatives.

Axer, 449

Bachmann, 445-6, 449
Baker, 443

Berger, 444, 446 (443)
Bervi, 451

Borel and Drach, 449
Bougaief (Bugaiev), 442-3,
449-451 (448)

Cahen, 449

CeslLro, 443, 450
Cistiakov, 451

Dedekind, 441-2 (444, 446)
Dirichlet, (445)

Elliott, 447

Fatou, 448
Fleck, 448
Furlan, 448

Gegenbauer, 447, 450 (443)
Glaisher, (441)

Hackel, 448

Kluyver, 448
Knopp, (448)

Kronecker, 447 (443, 448)
Kusnetzov, 448

Laguerre, 442

Author Index

483

Landau, 448-9
L^meray, 447
Liouville, 441-2
Lipschitz, 445
Lucas, 445

Meissel, 441
Meissner, 448
Merry, 442 (444)

Mertens, 442, 446 (448)
Mobius, 441 (443)

Nazimov, (448)

Seliwanov, 446
SheUy, 451
Steffensen, 449

Stieltjes, 449

Tschistiakow, 451

Von Koch, 446
Von Sterneck, 444-6 (442,
448)

Zsigmondy, 444-5.

Ch. XX. Properties of the Digits of Numbers.

Agronomof, 464
Aiyar, 458
Andreini, 459, 461
Andreoli, 464
Anonymous, 454, 458

Barbier, 457
Barillari, 455
Barisien, 462
Barlow, 453
BerdeU^, 457
Bertrand, 455
Bianchi, 455
Biddle, 463
Booth, 455
Boutin, 461
Bouton, 460
Brocard, 464
Brownell, 453
Burg, 464

Calvitti, 461

Cantor, 455 (458)

Catalan, 456

Cattaneo, 463

Cesaro, 457 (461)

Crelle, 454 (456)

Cunningham, 458, 460, 462-4

Davey, 454
De Rocquigny, 457
De Sanctis, 459, 464
Dickson, 460
D'Ocagne, 457
Drot, 455

Emsmann, 455
Escott, 458, 462

Flood, 455

Fourrey, 465
Fran^ais, 454

Gegenbauer, 458
Gelin, 465
G^rardin, 461-2
Gergonne, 454
Glaisher, 456
Goormaghtigh, 464
Gnmert, 455

HaUiday, 465
Hauke, 459
Hayashi, 459
HiU, 453
Hoskins, 456

Ingleby, 455

Janichen, 462
Johnson, 458

Kessler, 457
Koppe, 461
Ki-aitchik, 458
Kraus, 458

Laisant, 456-8 (454)
Lemoine, 457, 464
Lewis, 463
Lucas, 458, 465

Mackay, 457
Maillet, 464
Malo, 461
Mansion, 456
Martin, 456
Metcalfe, 460
Moore, 460
Morel, 456

Moret-BIanc, 457
Moulton, 465

Nannei, 462

Osana, 465
O'Shaughnessy, 465

Pahnstrom, 458-9 (461)
Perkins, 456
PiccioU, 460
Plateau, 456 (460, 463)

Rutherford, 455

Saint, 453 (456)
Sampson, 455
Sebban, 464
Simmons, 457
Stasi, 463
Storr, 458
Strauss, 458
Suchanek, (459)
Szego, 462

Tagiuri, 460
Tanner, 456
Tedenat, 454
Teilhet, 460
Thi6, 463

Valentin, 459
VerceUin, 462
Von Schrutka, 464

Welsch, 464
Wertheim, 459
White, 465
Wiggins, 460
Witting, 462

Ziihlke, 461

SUBJECT INDEX.

Abundant, 3, 7, 11, 14, 15, 20,
31-3

Agreeable, 38, 458

Algebraic numbers, 86, 221,
245, 251, 322, 379, 417,
447-8

Aliquot parts, 3, 50-8

Amantes, 39

Amiable, 38, 41

Amicable, 5, 38-50

of higher order, 49, 50

triple, 50

Anatomiae numeronmi, 348

Approximation, 114-5, 158,
281-3, 318, 330-1, 352, 354,
411, 422-3, 430, 448 (see
asymptotic, mean)

Arrangement in cycles, 269

Arithmetical progression,
100-1, 114, 131, 336, (see
prime)

Associated numbers, 64-6, 73

Asj-mptotic, 119, 122, 126-7,
129-132, 134-6, 138, 144,
154-5, 214-5, 289, 291,
294, 301-2, 305-6, 308,
317-325, 328, 333, 416-9,
434-6, 438-440, 450 (see
approximation, mean)

Aurifeuillian, 386, 390

Base, 178, 182, 186, 199, 273,
338, 340-1, 354-5, 369,
373, 375, 379, 385, 398,
454, 456, 458-460, 463^
(see digits, periodic)

Befreundete, 38

Belongs (see exponent)

Bemoullian numbers, 100,
109, 110, 112, 140-1, 145-
6, 220, 274, 278, 309, 311

Bernoulli's function, 268, 325

Bertrand's postulate, 132,
413, 425, 435-6

Bilinear form, 409

Binomial coefficients, 59, 62,
67, 77, 91, 97, 99, 266-278

congruence, 92-5, 105,

175, 177, 204-222, 388, 391

, identical, 78,

82, 87-9, 94-5

Casting out nines, 337-346

Characters, 201, 415

Circular permutations, 75, 78,
81, 131, 136

(484)

Combinations, 77, 90-1, 106,

261, 281, 303, 410
Complementary fractions, 156
Congeneres, 39
Congruence (see binomial)

, cubic, 252-6, 262

, higher, 223-61

, identical, 73. 87-9

, involving factorials,

275-8, 428

-, irreducible, 84, 234-

52
, quartic, 254-5, 259,

260
Congruent form, 362

fractions, 258-9

series, 259

Conjugate functions, 444
Consecutive numbers, 147,

332, 353, 355, 373, 457 (see

product)
Continued fractions, 138,

158, 210, 363, 367-8, 381,

393, 399, 403, 408-9
Crib (see sieve)
Criteria for given divisor, 337
Cyclotomic function, 199, 245,

378, 383-5, 387-90, 418

Decimal (see periodic)
Defective, 3
Deficient, 3
Determinant, 77, 87, 97, 137,

149, 150-1, 226, 228, 231,

233, 261, 288, 295, 321,

336, 368, 399, 410-1, 444,

446

=c (modm), 155, 261

of Smith, 122-4, 127-

130, 136
Diatomic series, 439
Differences of order m, 62— i,

74, 78, 79, 204
two primes,

424-5

squares, 357
Digits, 81, 343, 353-4, 358,

360, 366, 438, 453-65
of perfect number, 7,

10, 17, 20

permuted in multi-

Digits, sum of, 263-4, 266,
272, 337-8, 342-3, 367, 455,
457-8, 461-4

Diminute, 3, 4

Equivalent fractions, 135
EucUdean number, 28
Euler's constant, 122, 134,

136. 281-3, 289, 294, 317-

24, 328-30

criterion, 67, 205

generalization of Fer-

mat's theorem, 60-89, 398,

400

numbers, 363

0-function, 82, 85,

110, 113-58, 182, 285-6,
293, 312, 333-6, 404, 434,
441-2, 446

, gener-
alized by Schemmel, 147

Jordan,

123, 132, 147, 252, 298-9

Exc^dant, 3

Excess E of divisors 4m-|-l
over divisors 4m-|-3, 281,
289, 293, 295-6, 300-1, 308,
318-9

of odd over even

divisors, 290-1, 317-8

Exclusion method, 207, 369-
70

Exponent, 61, 112, 163, 169,
181-204, 240, 242-3, 246,
257, 259, 260 (see Haupt)

to which 10 belongs,

159-204, 339, 341-2

2 be-
longs, 111, 181, 190-1, 193,
198, 200, 203, 369-70

Factor tables, 347 (see graph-
ical)

Factorial, 62-3, 77, 263-78

Factoring, 13, 25, 241, 248,
252, 357 (see graphical, cri-
teria, sieve)

, number of ways of,

52, 109, 282, 285, 298, 331

Factors of 10" ±1, 159-179
— 2''-l (see per-

ples, 164-5, 170, 174, 176-7,
458-9

feet)

381-91

a^^b", 258,

Subject Index

485

Farey series, 155-8
Fermatian function, 385
Fermat's numbers 22° +1, 94,
140, 199, 375, 398, 401

theorem, 12, 17, 18,

59-89, 179

— , converse of,

— , generaliza-
tion, 84-9, 406 (see Galois)
Finite algebra, 388

differences, 250, 394,

91-5

407

field, 247, 250

Flachen Zahlen, 4
Frequency of a divisor, 126

Galois field, 232, 247, 250

imaginary, 233-55

Galois' generalization of Fer-
mat's theorem, 235, 240,
246-7, 249, 250, 252, 403

Wil-
son's theorem, 240, 246-7,
252

Gaussien, 194

Graphical factoring, 351, 353-
4, 356, 365, 369, 372, 374

representation of di-
visors, 330, 351, 354

Greatest common divisor,
139, 147, 150, 252, 328,
332-6, 394, 401-3, 447,
456, 462 (see determinant
of Smith)

di\asor, 329, 331

integer in, 89, 119,

121-2, 126, 130, 132, 138,
144, 153, 158, 263, 282,
293, 295, 297-9, 302-3,
319, 427, 429-432, 450-1

Goldbach's theorem and anal-
ogues, 421-5

Golden section, 411

Ground forms, 268

Groups, 78, 80-1, 84-5, 131,
137, 152, 155, 177, 194,
196-8, 201, 203, 216, 221,
248, 251, 268, 287, 332,
356, 414-5

Haupt-exponent, 190, 200, 203

Hexagon, 9, 411

Highest prime power in m.\,
263, 272

a poly-
nomial, 334

Highly composite number, l323

History, 32, 84, 157, 200,
342, 353

Hyper-even number, 379

Hyper-exponential number,
379

Idoneal (idoneus), 361-5
Imperfectly amicable, 50
Index, 85, 182-3, 185, 188,

190-4, 197-204, 211, 240,

244-5, 249, 251
Indian, 337
Indicator, 118, 131, 155, 186,

194, 200
Indivisibilis, 6
Integral logarithm, 353, 417,

440
Invariant, 89, 232-3, 260, 364
Inversion, 84, 120, 127, 129,

132-3. 135, 140, 145, 150,

153, 234, 296, 429, 430,

441-8
Irreducible function, 234-252
fraction, 126, 129,

133, 138, 155-8; 162, 175

Kerne, 334
Korper Zahlen, 4
Kronecker's plane, 155

Lattice, 173

Leaf arrangement, 411

Least common multiple, 82,

328, 332-6, 445, 464

residue, 341-2,344,369

Legendre-Jacobi symbol, 109,

210,219,249,251,255,260,

276, 288, 300, 308, 330, 364,

382, 385, 394, 398
Linear differential form, 248,

250
forms of divisors, 160,

362-4, 370, 382, 386, 390,

399
function, 117-8, 134,

204-5

nimabers, 4

Lucas' un, vn, 218, 395, 418
Lucassian, 27

Mangelhaft, 3

Matrix, 137, 226, 228, 233

Maximum divisor, 332

Mean, 281, 291-4, 301-2, 305,
312, 318, 320, 328-331, 333,
335, 447 (see asymptotic)

Mediation, 156

Mersenne number, 31

Mobius' (Merten's) function
M(n), 86, 122, 127-9, 144-5,
148-9, 150-1, 265, 289, 322-
3, 329, 335, 431, 441-9, 462

gener-
alized, 135-6

Modular system, 88, 249,

251, 402
Mosaic, 212
Multinomial coefficient, 59,

266-78
Multiply perfect, 33

Nim (game), 460

Nombres associes, 50

Norm, 236, 252, 322

Normal order, 325

Nmnber of divisors, 51, 54,
135-6, 142, 279-325, 328,
443, 451

integers divis-
ible by nth power, 327-32

solutions of

ui . . . ujk = n, 125, 149,291,
298, 308, 312, 317, 324

n = x'^y^,

318

Numerical integrals and de-
rivatives, 152, 449

Order modulo m, 138
of root, 189

Partial fraction, 73, 135, 161,

198, 410
Partition, 279, 290, 292, 303,

312, 427, 438
Patrone, 349

Pedal triangle, 86, 388, 402
Pell equation, 56, 367-8, 393
Pentagonal number, 279, 292,

312
Perfect number, 3-33, 38
of second kind,

58
Period, 133, 182, 202, 207
Periodic fraction, 75-6, 82,

92, 159-179, 193, 202, 339-

341, 371, 379, 386, 454
Pei-mutations, 78-80, 131, 136
Plateau's theorem, 456, 460,

463
Pluperfect, 33
Plus quam-perfectus, 3
Polygon, cm-viUnear, 85
, inscribed in cubic

curve, 85, 150

regular, 71, 75, 133,

139, 193, 375

Polynomial, divisors of, 384,
393^

in X divisible by m for

every x, 87, 89, 336

Primary function, 240

Prime functions (see irredu-
cible)

pairs, 353, 425, 438

486

Subject Index

Primes 6n=fcl, 7 (see differ-
ence, highest)

, asymptotic distribu-
tion of, 439, 449

, density of, 329, 416

in arith. progression.

425

-, infinity of, 413

arith. progressions, 85, 395,
415-20, 436

-, large, 352^, 362,

365, 386, 388

-, law of apparition of.

396, 398, 406
repeti-
tion of, 396-8

-, miscellaneous results

on, 436-9

-, number of, 352-4,

429-35, 450

, product of, 126

represented by quad-

ratic forms, 417
poly-
nomials, 333, 414, 418,
420-1

-, simi of two, 421-4,

435
Primes, tables of, 347, 381

, test for, 35, 276, 302,

305, 360-65, 370, 374, 376-
8, 380, 396-404, 426-8, 445
-, to base 2, 22, 353-4

Primitive diN-isor of a'^-b^, 388

X-root, 202

non-deficient number,

31

number, 327, 334

root, 63, 65, 72, 103,

117, 181-204, 222, 378-9
-, imaginarj'.

235-252

136

of unity, 133,

ProbabUity, 138, 302, 308,
328, 330, 333, 335, 407, 438

Product of consecutive inte-
gers, 79, 263-4, 269, 331

differences, 269

divisors, 58,

332

Pronic, 357

Quadratic forms, 109, 130,
158, 207, 210, 219, 276,
318, 330, 361-5, 369-70,
400, 415-8, 420-1

residues, 23, 25, 29,

65-8, 71, 76, 92, 109, 165,

185, 189, 190, 196-8, 202,
210, 213-4, 218, 221, 231,
240, 245-6, 253-5, 275,
277, 360, 363, 365, 373,
382, 393, 395-6, 403
Quasi-Mersenne number, 390
Quotient (a«'")-l)/m, 102,
10.5-112

[{}^l)\ + l]/p, 109,

112

Rank (see matrix)
Recurring series, 376-7, 393-

411
, algebraic the-

or\- of, 407
Reducible law of recurrence,

409-10
Redundantem, 3, 4
Remainders on di\dding n by

1, . . . , n, 290, 313, 327-31
Roots of unity, 133, 136, 183-

4, 245, 250, 256, 419

Secondary nimaber, 327

root, 191

Series of composition, 332

Lame, 411

Leonardo Pis-

ano, 393
Sieve of Eratosthenes, 8,

347-8, 353-6, 424, 439
Similar modulo k, 260
Simple sj'stem of numbers,

455, 458
Solution of alg. equations,

407-8
Sous-double, 33
Squares, 52, 54, 284-6, 358,

361, 366, 453-464
Stencil, 349, 356, 359
Substitutions, 75, 78-80, 82,

85, 158, 232, 262
Sum of divisors, 5, 18, 19,

22, 42, 48, 52-8, 135, 139,

279-325, 445, 450
A-th powers of

divisors, 38, 123, 151, 286-

325, 450
integers

<n, 95, 106, 121, 123, 126,

140, 332

four squares, 283

two squares.

247, 286, 340, 360, 381-2,

390, 402-3
Superfluos, 3, 4
SymboUc, 99, 119, 124, 141-2,

144-5, 148, 248, 250, 278,

296, 395, 399, 402, 449

Symbols, Ein), 281; Er{n),
296; F{a, N), M; Fr, 375;
H{m), Hm, 264; Jkin), 147;
Mg, 31; nin), 441; 0,305;
Pm, 33; <^(n), 61, 113;
(pkin), 140; qu, 105, 109;
s^in), 48; s„, 95; 5„, „,, 96;
a(n), 53, 279, 446; akin),
rin),T{n),279; n(n),291;
d(n),429; f/„,u„,393; ?(«),
292; [x], 115, 276; /n, 42;
*before author, not avail-
able.

Symmetric functions mod.
p, 70, 95, 106, 143

number, 112, 455,

463-4 •.

Tables, 10, 14, 16, 18, 21-2,
25, 27, 30-2, 37-8, 45,
48-9, 54-5, 110-2, 126, 135,
137, 140, 156-7, 160-79,
181, 183, 185, 187-203, 213,
217, 219, 222, 244-5, 248-
51, 254, 262, 296, 308, 318,
331, 339-41, 347-58, 361^,
366-7, 379, 381-4, 386, 388,
390-1, 399, 417, 422, 432,
446, 457

Tahnud, 337

Totient, 124-5, 148, 153, 246

point, 154

Totitives, 98, 124, 130-1, 246

all primes, 132, 134

Triangular number, 7, 9, 20,
59, 284, 290, 295, 302, 310,
373, 425, 427

Trinomials, factors of, 391

Uberflussig, 3
Uberschiessende, 3
tJbervollstandig, 3
Unvollkommen, 3
Unvollstiindig, 3

Verwandte, 38, 47
Vollkommen, 3
Vollstandig, 3

Wilson's theorem, 59-91, 99,

103, 275
, converse of,

63, 427-8
, generalization

of, 65, 68-74, 77-84, 87,

90-1 (see Galois)

Zeta function, 121, 125-7,
134, 139, 149, 292-3, 298-9,
310,318,322,324,328,331,
439, 448

486

Subject Index

Primes 6n±l, 7 (see differ-
ence, highest)

, asymptotic distribu-
tion of, 439, 449

, density of, 329, 416

in arith. progression,

425

-, infinity of, 413

arith. progressions, 85, 395,
41.S-20, 436

-, large, 352^, 362,

365, 386, 388

-, law of apparition of.

396, 398, 406
repeti-
tion of, 396-8

-, miscellaneous results

on, 436-9

-, number of, 352-4,

429-35, 450

, product of, 126

represented by quad-
ratic forms, 417

poly-
nomials, 333, 414, 418,
420-1

-, sum of two, 421-4,

435

Primes, tables of, 347, 381
, test for, 35, 276, 302,

305, 360-65, 370, 374, 376-

8, 380, 396-404, 426-8, 445

, to base 2, 22, 353-4

Primitive diN-isor of a^-b", 388

X-root, 202

non-deficient number,

31

number, 327, 334

root, 63, 65, 72, 103,

117, 181-204, 222, 378-9
, imaginary-.

235-252

136

of unity, 133,

Probability, 138, 302, 308,
328, 330, 333, 335, 407, 438

Product of consecutive inte-
gers, 79, 263-4, 269, 331

differences, 269

divisors, 58,

332

Pronic, 357

Quadratic forms, 109, 130,
158, 207, 210, 219, 276,
318, 330, 361-5, 369-70,
400, 415-8, 420-1

residues, 23, 25, 29,

6&-8, 71, 76, 92, 109, 165,

185, 189, 190, 196-8, 202,

210, 213-4, 218, 221, 231,

240, 245-6, 253-5, 275,

277, 360, 363, 365, 373,

382, 393, 395-6, 403
Quasi-Mersenne number, 390
Quotient (a*"')-l)/m, 102,

10.5-112
{{p-l)\ + l}/p, 109,

112

Rank (see matrix)
Recurring series, 376-7, 393-

411
, algebraic the-

or>' of, 407
Reducible law of recurrence,

409-10
Redundantem, 3, 4
Remainders on dividing n by

1, . . . , n, 290, 313, 327-31
Roots of unity, 133, 136, 183-

4, 245, 250, 256, 419

Secondary nrnnber, 327

root, 191

Series of composition, 332
Lame. 41 1

ano, 393 JohS^.h^.^^. Date

Sieve of Eratostb ^ ^ ^ ^ime

347-8,353-6,424, ^^^^"""^^

Similar modulo k, 26l Stab by No. Sect Sew by.

Simple system of r

455, 458

This book bound by Pacific Library Binding
Company, Los Angeles, specialists in Library
Binding. Our work and materials are guaranteed
to wear indefinitely to satisfaction of purchaser, and

Symbols, E(n), 281; Er{n),
296; Fia, N),84; Fr, 375;
Him), Hm, 264; Jkin), 147;
Mg, 31; M(n), 441; 0, 305;
Pm, 33; <^(n), 61, 113;
<j)k{n), 140; qu, 105, 109;
sHn), 48; s„, 95; 5„. m, 96;
a(n), 53, 279, 446; akin),
Tin), Tin), 279; Tkin),291;
ein),429; C/„,u„,393; f(s),
292; [x], 115, 276; fn, 42;
*before author, not avail-
able.

Symmetric functions mod.
p, 70, 95, 106, 143

number, 112, 455,

463-4 •

Tables, 10, 14, 16, 18, 21-2,
25, 27, 30-2, 37-8, 45,
48-9, 54-5, 110-2, 126, 135,
137, 140, 156-7, 160-79,
181, 183, 185, 187-203, 213,
217, 219, 222, 244-5, 248-
51, 254, 262, 296, 308, 318,
331, 339-41, 347-58, 361^,
366-7, 379, 381-4, 386, 388,
390-1. 399. 417. 422. A^9.

Score Press Strip Sect.

Solution of alg. ec

407-8
Sous-double, 33 .„ - . • j ■

SnnnrP9 ^9 ^4 984 anv defects appearing in either will be made good
isquares, O^, t>% ^»4 ;jj^ ^ additional charge. "Bound to wear."

361, 366, 453-464
Stencil, 349, 356, 35{
Substitutions, 75, 78-80, 82,

85, 158, 232, 262
Sum of divisors, 5, 18, 19,

22, 42, 48, 52-8, 135, 139,

279-325, 445, 450

A:th powers of

divisors, 38, 123, 151, 286-

325, 450
integers

<n, 95, 106, 121, 123, 126,

140, 332

four squares, 283

two squares.

247, 286, 340, 360, 381-2,

390, 402-3
Superfluos, 3, 4
Symbolic, 99, 119, 124, 141-2,

144-5, 148, 248, 250, 278,

296, 395, 399, 402, 449

Ubervollstandig, 3
Unvollkommen, 3
Unvollstandig, 3

Venvandte, 38, 47
^'ollkommen, 3
Vollstiindig, 3

Wilson's theorem, 59-91, 99,

103, 275
, converse of,

63, 427-8
, generalization

of, 65, 68-74, 77-84, 87,

90-1 (see Galois)

Zeta function, 121, 125-7,
134, 139, 149, 292-3, 298-9,
310,318,322,324,328,331,
439, 448

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