OFFSET
1,3
COMMENTS
Primes found and proved by PrimeForm. No more terms up to 20000.
a(6) and a(7) proved prime by the primality proving program LLR. - Robert Price, Jan 06 2016
a(8) > 2*10^5. - Robert Price, Jan 06 2016
MATHEMATICA
Join[{0}, Select[Range[1, 261, 2], PrimeQ[2*23^# + 1] &]] (* Arkadiusz Wesolowski, Nov 06 2012 *)
PROG
(PARI) is(n)=ispseudoprime(2*23^n+1) \\ Charles R Greathouse IV, Feb 20 2017
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Rick L. Shepherd, Jul 05 2008
EXTENSIONS
a(6)-a(7) from Robert Price, Jan 06 2016
STATUS
approved