Fermat’s last theorem states that the equation `x`^{n} + `y`^{n} = `z`^{n} has no solutions in integers `x`, `y`, `z`, and `n` where `n` > 2. Try this in a calculator: 1782^{12} + 1841^{12} = 1922^{12}.

That equation was generated by a program written by David X Cohen, at the time a writer for The Simpsons, subsequently executive producer of Futurama. He put it in the background of the three-dimensional realm in the episode Homer^{3}. It’s not a counter-example to the theorem—which at the time hadn’t been completely proved, but had been proved up to a certain exponent (much higher than 12)—but it will look like one on any calculator that truncates numbers after ten or fewer digits.

Found in a mathematical interview with Cohen.