Selfridge-Hurwitz Residue
Let the Residue from Pépin's Theorem be
where
is a Fermat Number. Selfridge and Hurwitz use
A nonvanishing
indicates that is Composite for 
.See also Fermat Number, Pépin's Theorem
References
Crandall, R.; Doenias, J.; Norrie, C.; and Young, J. ``The Twenty-Second Fermat Number is Composite.'' Math. Comput. 64, 863-868, 1995.
- Odd Number Theorem
- Odd Order Theorem
- Odd Prime
- Odds
- Odd Sequence
- ODE
- Offset Rings
- Ogive
- Oldknow Points
- Omega Constant
- Omega Function
- Omino
- Omnific Integer
- O'Nan Group
- Onduloid
- One
- One-Form
- One-Mouth Theorem
- One-Ninth Constant
- One-to-One
- One-Way Function
- Only Critical Point in Town Test
- Onto
- Open Disk
- Open Interval