Fermat’s Little Theorem


This is a beautiful theorem which states that the difference between a positive integer a and a prime power of a, a^p-a, is divisible by p. It’s history can be found in Wikipedia: Fermat posited the theorem (and as usual, did not give the proof) while Euler first published a proof using mathematical induction. Below, we will state the theorem and provide a simple-to-understand proof using only modular arithmetic, followed by another simple proof using mathematical induction.

Continue reading “Fermat’s Little Theorem”