1. What is Fermat's Little Theorem
If p is a prime number and the integer a is not a multiple of p, then
ap − 1 ≡ 1 ( modp ) a^{p-1}\,≡1(mod p)ap−1≡1 （m o d p ）
2. Proof of Fermat's Little Theorem
Fermat's little theorem (easy to understand) - Gan Yi's article - Know
the proof of Fermat's little theorem
3. Quick Power
Algorithm Study Notes (4): Fast Power - Pecco's Article - Zhihu
Fast Power Explained Detailed Version
Reprinted from:
Fast Power Explained Non-recursive Detailed Version