A141798 Numbers n such that 2*23^n + 1 is prime.

0, 1, 5, 21, 261, 47589, 93337

Offset: 1

Author

Rick L. Shepherd, Jul 05 2008

Keywords

• hard
• nonn

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

Crossrefs

Cf. A141774, A141797, A141802, A190942, A068231.

Programs

Mathematica

Join[{0}, Select[Range[1, 261, 2], PrimeQ[2*23^# + 1] &]] (* Arkadiusz Wesolowski, Nov 06 2012 *)

PARI

is(n)=ispseudoprime(2*23^n+1) \\ Charles R Greathouse IV, Feb 20 2017

Extensions

a(6)-a(7) from Robert Price, Jan 06 2016