A very helpful book. The book has few drawbacks if you are looking for a more modern perspective on number theory. However, those drawbacks are barely noticeable. One of the most beautiful features besides the mathematical ease of reading and presentation is the little stories about Euler, Fermat, Lagrange, and multitude of other mathematicians. It is a story of developments of number theory in the hands and minds of few brilliant number theorists distributed across the ages scattered across the globe. A marvelous book!
The book is extremely constructive and helpful. Burton helps you every step of the way with his hints littered across every exercise. A very easy read. However, lack of recent developments might be wanting but any undergraduate getting introduced to number theory will appreciate the number of open problems Burton introduces in his text with relevant information. Topics covered include Euclid's theorem, Mobius' inversion, primality, primitive roots (a glimpse in to Group Theory), modular arithmetic/congruences, quadratic reciprocity, Legendre and Jacobi symbols, QNR, Pell's equation, Pythagorean numbers, Fermat conjectures and theorems, Wilson' theorem, infinite fractions, CRT, and several minor topics, not necessarily in order of mentioning.
I would recommend this book to any student taking a first course in Number Theory despite the lack of some topics in any elementary Number Theory Course. Simply because of the excellent ease of reading and writing style.