The works of the 17th-century mathematician Pierre de Fermat engendered many theorems. Fermat's theorem may refer to one of the following theorems:
Fermat's Last Theorem, about integer solutions to an + bn = cn
Fermat's little theorem, a property of prime numbers
Fermat's theorem on sums of two squares, about primes expressible as a sum of squares
Fermat's theorem (stationary points), about local maxima and minima of differentiable functions
Fermat's principle, about the path taken by a ray of light
Fermat polygonal number theorem, about expressing integers as a sum of polygonal numbers
Fermat's right triangle theorem, about squares not being expressible as the difference of two fourth powers