Number theory is the branch of mathematics that studies properties of the integers (..., -2, -1, 0, 1, 2,...). Despite being around for thousands of years, there are still many fundamental unsolved problems. Come learn about modular arithmetic, which helps explain quick methods for testing if a number is divisible by 11. Or Fermat's Little Theorem, which forms the basis for a powerful technique for quickly checking if a number is prime.