I will post useful materials for studying mathematical olympiads in this page.

My books:

My problem sets:

Number theory books:

Number Theory Structures, Examples, and Problems – Titu Andreescu and Dorin Andrica

An Introduction to Diophantine Equations – Titu Andreescu, Dorin Andrica, Ion Cucurezeanu

104 Number Theory Problems – Titu Andreescu, Dorin Andrica, Zuming Feng

Here is a list of useful number theory books/notes which can be downloaded from this website:

Number Theory – Naoki Sato

Elementary Number Theory – W. Edwin Clark

Numbers and Curves (book draft, Springer, 2001) – Franz Lemmermeyer

Algorithmic Number Theory (web draft, 2002) – S. Arun-Kumar

Elementary Number Theory: Primes, Congruences, and Secrets – William Stein
 250 Problems in Elementary Number Theory – Waclaw Sierpinski

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