Trap Door

Pierre Fermat, 1640.

Fermat's Little Theorem:  if x is an integer which is not divisible by a prime p, then

Proof (not Fermat's)

The number of positive integers less than or equal to p which don't have any common factors with p is p-1, since p is a prime.  Then Fermat's Little Theorem follows from Euler's Theorem.

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