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Pépin's Theorem

The Fermat number F_n is prime iff

3^(2^(2^n-1))=-1 (mod F_n).

See also

Fermat Number, Pépin's Test, Selfridge-Hurwitz Residue

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Cite this as:

Weisstein, Eric W. "Pépin's Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/PepinsTheorem.html

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