Fermat's Last Theorem

Theorem
$$\forall a, b, c, n \in \Z^*, \; n > 2$$, the equation $$a^n + b^n = c^n$$ has no solutions.

Proof
The proof of this theorem is beyond the current scope of ProofWiki, and indeed, is beyond the understanding of many high level mathematicians. For the curious reader, the proof can be found here, in a paper published by Andrew Wiles, entitled "Modular elliptic curves and Fermat's Last Theorem", in volume 141, issue 3, pages 443 through 551 of the Annals of Mathematics.

Historical Note
As Fermat himself put it:

"Cubum autem in duos cubos, aut quadratoquadratum in duos quadratoquadratos et generaliter nullam in infinitum ultra quadratum potestatem in duos ejusdem nominis fas est dividere: cujus rei demonstrationem mirabilem sane detexi. Hanc marginis exiguitas non caperet."

Loosely translated from the Latin, that means:

"The equation $$x^n + y^n = z^n$$ has no integral solutions when $$n > 2$$. I have discovered a perfectly marvellous proof, but this margin is not big enough to hold it."

Fermat wrote this in the margin of his copy of Diophantus' Arithmetica and claimed to have found a proof of it. Nobody managed to find such a proof, till it was finally proved by Andrew Wiles in 1984. It is seriously doubted that Fermat actually had found a general proof of it.