Tom M. Apostol

This book is the first part of a two-volume textbook for undergraduate students. It is, in fact, the crystallization of a course the author taught at the California Institute of Technology to undergraduate students who had no prior understanding of number theory. Because of this, the book’s first section covers some of the most fundamental characteristics of natural numbers. Despite this, the book manages to pack an incredible amount of information into just more than 300 pages.