A032500 Numbers k such that 247*2^k+1 is prime.

6, 14, 18, 26, 34, 42, 56, 74, 78, 94, 132, 146, 186, 284, 302, 1758, 1816, 2336, 3374, 3466, 4522, 8058, 11114, 12456, 22172, 26208, 39794, 61512, 81576, 238734, 270794, 348972, 420034, 680694, 682974, 964444, 1076024, 1124806, 1158186, 1786968, 2082202

Offset

1,1

Links

Jeppe Stig Nielsen, Table of n, a(n) for n = 1..42

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[247*2^# + 1] & ] (* Robert Price, Dec 20 2018 *)

Prog

(PARI) is(n)=ispseudoprime(247*2^n+1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A260114 A340634 A156858 * A053474 A072204 A037177

Adjacent sequences: A032497 A032498 A032499 * A032501 A032502 A032503

Keyword

nonn,hard

Author

N. J. A. Sloane.

Extensions

a(30)-a(40) from the Ray Ballinger and Wilfrid Keller link by Robert Price, Dec 20 2018

a(41) from Jeppe Stig Nielsen, Jan 19 2020

Status

approved