A032481 Numbers k such that 209*2^k+1 is prime.

1, 5, 11, 13, 65, 113, 299, 335, 1235, 1991, 2861, 3295, 3343, 3901, 5545, 9125, 10769, 14303, 19433, 28535, 76855, 206821, 207223, 530729, 1172111, 1992071

Offset

1,2

Links

Table of n, a(n) for n=1..26.

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[209*2^# + 1] & ] (* Robert Price, Dec 19 2018 *)

Prog

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

Crossrefs

Sequence in context: A115091 A034924 A018607 * A365502 A348313 A352534

Adjacent sequences: A032478 A032479 A032480 * A032482 A032483 A032484

Keyword

nonn,hard,more

Author

N. J. A. Sloane.

Extensions

a(22)-a(26) from the Ray Ballinger and Wilfrid Keller link by Robert Price, Dec 19 2018

Status

approved