A032502 Numbers k such that 251*2^k+1 is prime.

1, 11, 13, 17, 35, 77, 155, 325, 4097, 5471, 7151, 7561, 9211, 13535, 14627, 18361, 21815, 41945, 68255, 105947, 119915, 358777, 748745, 843367, 1171193, 2730917

Offset

1,2

Links

Table of n, a(n) for n=1..26.

Ray Ballinger, Proth Search Page

Ray Ballinger and Wilfrid Keller, List of primes k.2^n + 1 for k < 300

Wilfrid Keller, List of primes k.2^n - 1 for k < 300

Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

Mathematica

Select[Range[1000], PrimeQ[251*2^# + 1] & ] (* Robert Price, Dec 20 2018 *)

Prog

(PARI) is(n)=ispseudoprime(251*2^n+1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A090236 A240623 A240624 * A209871 A347702 A167794

Adjacent sequences: A032499 A032500 A032501 * A032503 A032504 A032505

Keyword

nonn,hard,more

Author

N. J. A. Sloane.

Extensions

a(21)-a(25) from the Ray Ballinger and Wilfrid Keller link by Robert Price, Dec 20 2018

a(26) from Jeppe Stig Nielsen, Feb 25 2020

Status

approved