Sums of squares -- Number Theory 26
39:08
Quadratic Forms -- Number Theory 27
17:09
A challenging divisibility problem!
18:36
complex numbers tells us that the factorial is very special
19:50
FUN Ecuadorian Math Olympiad Number Theory Problem
11:06
Elementary Number Theory by Underwood Dudley
33:59
Why was this visual proof missed for 400 years? (Fermat's two square theorem)
9:57
When is a prime the sum of two squares? — The Ross Program
1:02:35