An Etymological Dictionary of Astronomy and Astrophysics
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A → Fermat number, 2²ⁿ + 1, that is a → prime number. The only known Fermat primes are: 3, 5, 17, 257, and 65537, corresponding to n = 0, 1, 2, 3, and 4.

→ Fermat's principle; → prime.