OFFSET
1,1
COMMENTS
p divides A123591(p) for prime p > 2.
Odd composite numbers k such that (2^k-1)^(2^k) == 1 (mod k). - Robert Israel, Jul 06 2017
LINKS
Robert Israel, Table of n, a(n) for n = 1..571
MAPLE
select(n -> not isprime(n) and (2^n-1) &^ (2^n) mod n = 1, [seq(i, i=9..10000, 2)]); # Robert Israel, Jul 06 2017
MATHEMATICA
Do[f=PowerMod[(2^n-1), (2^n), n]-1; If[ !PrimeQ[n]&&IntegerQ[(n+1)/2]&&IntegerQ[f/n], Print[n]], {n, 2, 10000}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Jan 22 2007
STATUS
approved