A generalization of Fermat's Little Theorem. Euler published a proof of the following more general
theorem in 1736. Let denote the Totient Function. Then
See also Chinese Hypothesis, Euler's Displacement Theorem, Euler's Distribution Theorem, Fermat's Little Theorem, Totient Function
Shanks, D. Solved and Unsolved Problems in Number Theory, 4th ed. New York: Chelsea, p. 21 and 23-25, 1993.