Let the residue from Pépin's theorem be
where is a Fermat number. Selfridge and Hurwitz use
A nonvanishing indicates that is composite for .
Let the residue from Pépin's theorem be
where is a Fermat number. Selfridge and Hurwitz use
A nonvanishing indicates that is composite for .
Weisstein, Eric W. "Selfridge-Hurwitz Residue." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Selfridge-HurwitzResidue.html