Armendariz E., McAdam S. Elementary number theory 1980

Textbook in PDF format

Rules of the Game
The Integers
Well-Ordering
Induction
Exercises
Divisibility
Division
Greatest Common Divisors
The Equation aX+bY = c
Exercises
Prime Numbers
Primes
A Sieve Method
Fermat Factorization
Some Unsolved Problems
Exercises
Congruences
Congruence
Inverses Modulo m
Fermat’s Little Theorem
Euler’s Theorem
A Historical View
Wilson’s Theorem
Exercises
Multiplicative Functions
Three Special Functions
Perfect Numbers
Mobius Inversion
Exercises
Solving Congruences
The Congruence aX = b mod m
Systems of Linear Congruences
The Congruence
= a mod m
General Theorem
Exercises
Sums of Squares
Pythagorean Triples
Sums of Two Squares
Sums of Four Squares
Exercises
Primitive Roots
Exercises
Quadratic Reciprocity
The Legendre Symbol
The Quadratic Reciprocity Theorem
Exercises
Table of Squares
Table of Primes Less Than 10,000
Index