Pierre de Fermat

French mathematician Pierre de Fermat had noted that although there are plenty of solutions to the equation X2 + Y2 = Z2 (for example, 32 + 42 = 52), there is no corresponding solution if the numbers are cubed instead of squared. In fact, Fermat scribbled in the margin of a book that he had "truly marvelous" proof that the equation Xn + Yn = Zn has no solution if n is any number greater than 2. Unfortunately, he never put his proof on paper.