A050897 Numbers k such that 277*2^k-1 is prime.

5, 21, 101, 105, 333, 461, 933, 1041, 2157, 3321, 5177, 5513, 5781, 9737, 11505, 16457, 17357, 490805

Offset

1,1

Links

Table of n, a(n) for n=1..18.

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

Prog

(PARI) is(n)=ispseudoprime(277*2^n-1) \\ Charles R Greathouse IV, Jun 13 2017
(Python)
from sympy import isprime
def afind(limit, startat=0):
  pow2 = 2**startat
  for k in range(startat, limit+1):
    if isprime(277*pow2-1): print(k, end=", ")
    pow2 *= 2
afind(3333) # Michael S. Branicky, May 21 2021

Crossrefs

Sequence in context: A201869 A017968 A017969 * A338673 A199215 A204061

Adjacent sequences: A050894 A050895 A050896 * A050898 A050899 A050900

Keyword

hard,nonn

Author

N. J. A. Sloane, Dec 29 1999

Extensions

490805 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

Status

approved