Euler's Totient Theorem

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

for all  relatively prime to .

REFERENCES:

Séroul, R. "The Theorems of Fermat and Euler." §2.8 in Programming for Mathematicians. Berlin: Springer-Verlag, p. 15, 2000.

Shanks, D. Solved and Unsolved Problems in Number Theory, 4th ed. New York: Chelsea, p. 21 and 23-25, 1993.