I. Niven, H. S. Zuckerman, H. L. Montgomery - An Introduction to the Theory of Numbers, Publisher: Wiley, 5th Edition

J. H. Silverman, A Friendly Introduction to Number Theory, Publisher: Pearson, 4th Edition

H. Davenport - The Higher Arithmetic, Publisher: Cambridge, 8th Edition

N. Koblitz - A Course in Number Theory and Cryptography, Springer

W. Stein - Elementary Number Theory: Primes, Congruences, and Secrets