A128001 Numbers k such that (k-1)*2^k + 1 is prime.

2, 3, 7, 27, 51, 55, 81, 1471, 1483, 8668, 10885, 20803, 32605, 36391, 57004, 61627, 88651, 89731, 133928, 153428

Offset: 1

Author

N. J. A. Sloane, Jan 25 2008

Keywords

• nonn
• more

Crossrefs

Cf. A029544, A002064, A196303.

Programs

Mathematica

Select[Range[200], PrimeQ[(# - 1)*2^# + 1] &]  (* G. C. Greubel, May 08 2018 *)

PARI

is(n)=ispseudoprime((n-1)<Charles R Greathouse IV, Jun 06 2017

Extensions

a(8)-a(14) from Jason Earls, Jan 29 2008

a(15)-a(18) from Charles R Greathouse IV, Oct 09 2011

a(19)-a(20) from Michael S. Branicky, May 14 2025