A note scribbled in a book's margin took 358 years to prove
Around 1637, Pierre de Fermat wrote in the margin of a book that no three positive whole numbers a, b and c can satisfy a^n + b^n = c^n for any whole number n greater than 2 — and claimed to have a proof too large to fit in the margin. Generations of mathematicians tried and failed to reconstruct it.
Reveal the answer
British mathematician Andrew Wiles finally proved it in 1994, using techniques from elliptic curves and modular forms that didn't exist in Fermat's lifetime — strong evidence Fermat's original 'proof' was mistaken or never existed. Wiles had worked on it secretly for seven years and needed to patch a serious gap discovered after his first announcement before the proof was accepted.
— Pierre de Fermat; proved by Andrew Wiles, Fermat's Last Theorem — Conjectured c. 1637, proved 1994