Linked from
The 28 pages that link to Fermat's little theorem, each with the reason it gives.
Congruence (number theory)Related: It reduces large powers in calculations modulo a prime.
Coprime integersRelated: Its condition that p does not divide a is exactly coprimality with p.
Sophie Germain's theoremRelated: Congruences derived from this theorem help control powers modulo p.
Artin's conjecture on primitive rootsRelated: It bounds every nonzero residue's order by p−1.
Proth's theoremRelated: Its exponent congruence underlies the prime direction of Proth's test.