A050541 Numbers k such that 31*2^k-1 is prime.

1, 5, 7, 11, 13, 23, 33, 35, 37, 47, 115, 205, 235, 271, 409, 739, 837, 887, 2189, 3465, 4653, 5073, 8011, 8061, 21957, 24589, 25657, 44653, 50321, 57647, 62083, 78179, 80021, 81655, 111667, 150265, 177089, 196433, 274115, 306751, 311389, 315523, 406105, 421129

Offset

1,2

Comments

773227 is also in the sequence. - Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

Links

Table of n, a(n) for n=1..44.

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

Kosmaj, Riesel list 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[31*2^# - 1] & ] (* Robert Price, Dec 22 2018 *)

Prog

(PARI) is(n)=ispseudoprime(31*2^n-1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A032365 = 31*2^n+1 is prime.

Sequence in context: A349459 A216770 A216736 * A098865 A022885 A176831

Adjacent sequences: A050538 A050539 A050540 * A050542 A050543 A050544

Keyword

nonn

Author

N. J. A. Sloane, Dec 29 1999

Extensions

More terms from Hugo Pfoertner, Aug 29 2004

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(43)-a(44) from the Wilfrid Keller link by Robert Price, Dec 22 2018

Status

approved