A050856 Numbers k such that 209*2^k-1 is prime.

4, 8, 16, 28, 40, 52, 80, 148, 328, 8464, 11704, 52372, 60172, 675232, 692692, 921484

Offset

1,1

Links

Table of n, a(n) for n=1..16.

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[209*2^# - 1] & ] (* Robert Price, Dec 29 2018 *)

Prog

(PARI) is(n)=ispseudoprime(209*2^n-1) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Sequence in context: A273080 A020193 A176817 * A271649 A128441 A009861

Adjacent sequences: A050853 A050854 A050855 * A050857 A050858 A050859

Keyword

hard,nonn,more

Author

N. J. A. Sloane, Dec 29 1999

Extensions

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

a(16) from the Wilfrid Keller link by Robert Price, Dec 29 2018

Status

approved