A296031 Numbers k such that 2^(k-1) - k is prime.

5, 11, 15, 17, 27, 51, 57, 71, 117, 2073, 6251, 13671, 14217, 14627

Offset

1,1

Comments

a(15) > 200000. - Giovanni Resta, May 13 2018

Links

Table of n, a(n) for n=1..14.

Formula

a(n) = A099439(n) + 1 = A063791(n) + 2.

Example

5 is in the sequence, because 2^4 - 5 = 11 is prime.

Mathematica

Select[Range[6500], PrimeQ[2^(# - 1) - #] &] (* Michael De Vlieger, Apr 21 2018 *)

Prog

(PARI) forstep(n=1, 10^6, 2, if(ispseudoprime(2^(n-1)-n), print1(n, ", "))); \\ Joerg Arndt, Apr 15 2018

Crossrefs

Cf. A063791, A099439.

Sequence in context: A137003 A314003 A314004 * A344214 A314005 A164355

Adjacent sequences: A296028 A296029 A296030 * A296032 A296033 A296034

Keyword

nonn,more

Author

Thomas Gajdek, Dec 03 2017

Extensions

Edited by Joerg Arndt, Apr 15 2018

Status

approved