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A050897 Numbers k such that 277*2^k-1 is prime. 0
5, 21, 101, 105, 333, 461, 933, 1041, 2157, 3321, 5177, 5513, 5781, 9737, 11505, 16457, 17357, 490805 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 27 13:40 EDT 2021. Contains 348276 sequences. (Running on oeis4.)