OFFSET
1,20
COMMENTS
A base-2 Fermat pseudoprime is a composite number x such that 2^x = 2 mod x.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..419
Eric Weisstein's World of Mathematics, Pseudoprime
MATHEMATICA
Table[d=Divisors[2^n-1]; cnt=0; Do[m=d[[i]]; If[ !PrimeQ[m]&&PowerMod[2, m, m]==2, cnt++ ], {i, Length[d]}]; cnt, {n, 100}]
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
T. D. Noe, Jul 14 2003
STATUS
approved