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Fermat's Last Theorem

historic

Posed by Pierre de Fermat · 1637 · number theory · resolved 1995 · ~1 min read · difficulty 5/5

diophantine-equations modular-forms

The problem

Theorem: the equation \(x^n\) + \(y^n\) = \(z^n\) has no solutions in positive integers x, y, z when n > 2. Fermat noted in 1637 that he had a marvellous proof; the margin was too narrow to contain it. Proven by Andrew Wiles in 1995 via the modularity of semistable elliptic curves.

History & significance

Written by Fermat in his copy of Diophantus around 1637 with the fatal words "I have discovered a truly marvellous proof of this, which this margin is too narrow to contain." Euler settled n = 3; Dirichlet and Legendre n = 5; Kummer built ideal theory reaching all regular exponents. Sophie Germains partial programme anticipated modern approaches. In September 2026 the proof gained a second kind of certainty: Claude, working largely autonomously over 11 days on the Prove2Me platform, produced the first complete computer-checked formalization — about 13 million lines of Lean, 29,500 intermediate theorems, following the Darmon–Diamond–Taylor exposition and checked by Lean's kernel plus an independent second kernel. No new mathematics; the first end-to-end machine verification of a proof at this scale, building on Mathlib and Buzzard's community FLT project.