This book explains clearly and in detail the basic concepts and methods of calculations of the elementary theory of numbers. It consists of 7 chapters illustrated by numerous examples and exercises. Answers together with some hints to the exercises are given at the end of the book. It may be used as a textbook for undergraduate students.
Theory of divisibility; congruences; indeterminate equations; congruences in one unknown; quadratic residues and congruences of the second degree in one unknown; primitive roots and indices; brief introduction to the number theory.