A Fermat pseudoprime to a base , written psp(), is a Composite Number such that
(i.e.,
it satisfies Fermat's Little Theorem, sometimes with the requirement that must be Odd; Pomerance *et al. *1980).
psp(2)s are called Poulet Numbers or, less commonly, Sarrus Numbers or
Fermatians (Shanks 1993). The first few Even psp(2)s (including the Prime 2 as a pseudoprime)
are 2, 161038, 215326, ... (Sloane's A006935).

If base 3 is used in addition to base 2 to weed out potential Composite Numbers, only 4709 Composite Numbers remain . Adding base 5 leaves 2552, and base 7 leaves only 1770 Composite Numbers.

**References**

Pomerance, C.; Selfridge, J. L.; and Wagstaff, S. S. ``The Pseudoprimes to .'' *Math. Comput.*
**35**, 1003-1026, 1980. Available electronically from
ftp://sable.ox.ac.uk/pub/math/primes/ps2.Z.

Shanks, D. *Solved and Unsolved Problems in Number Theory, 4th ed.* New York: Chelsea, p. 115, 1993.

Sloane, N. J. A. Sequence
A006935/M2190
in ``An On-Line Version of the Encyclopedia of Integer Sequences.''
http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.
*The Encyclopedia of Integer Sequences.* San Diego: Academic Press, 1995.

© 1996-9

1999-05-26