Fermat's Last Theorem

http://en.wikipedia.org/wiki/Fermat%27s_Last_Theorem

After Fermat proved the special case n = 4, the general proof for all n required only that the theorem be established for all odd prime exponents.^[49] In other words, it was necessary to prove only that the equation aⁿ + bⁿ = cⁿ has no integer solutions (a, b, c) when n is an odd prime number. This follows because a solution (a, b, c) for a given n is equivalent to a solution for all the factors of n. For illustration, let n be factored into d and e, n = de. The general equation

aⁿ + bⁿ = cⁿ