Theorem: Let f(A,B,...) be a polynomial in any number of variables over Z,
and let
n be a positive integer. Define a polynomial F by
F(A,B,...) = sum_{d|n} M(d) f(A^d, B^d, ...)^{n/d}
where M denotes the Mobius function. Then all the coefficients of F are
divisible by n.
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Fermat's little theorem is the special case in which n is a prime and f is a
constant! :D
-- Larry