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, 396128

Offset: 1

Author

Thomas Gajdek, Dec 03 2017

Keywords

• nonn
• more

Comments

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

Examples

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

Crossrefs

Cf. A063791, A099439.

Programs

Mathematica

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

PARI

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

Formula

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

Extensions

Edited by Joerg Arndt, Apr 15 2018

a(15) from Michael S. Branicky, Apr 20 2025 using A099439