Fermat's little theorem

Fermat's Little Theorem states that if \( p \) is a prime number and \( a \) is an integer not divisible by \( p \), then the following congruence holds: \[ a^{p-1} \equiv 1 \mod p \] This means that when \( a^{p-1} \) is divided by \( p \), the remainder is 1.