A196303 Primes p such that (p-1)*2^p+1 is also prime.

2, 3, 7, 1471, 1483, 61627, 88651

Offset: 1

Author

Juri-Stepan Gerasimov, Oct 02 2011

Keywords

• nonn

Examples

			a(1) = 2 because 2 and (2-1)*2^2 + 1 = 5 are both prime.
a(2) = 3 because 3 and (3-1)*2^3 + 1 = 17 are both prime.
a(3) = 7 because 7 and (7-1)*2^7 + 1 = 769 are both prime.
		

Crossrefs

Prime terms of A128001.

Cf. A029544, A196421, A196446.

Programs

Mathematica

Select[Prime[Range[9000]],PrimeQ[(#-1)2^#+1]&] (* Harvey P. Dale, Jan 19 2012 *)

PARI

forprime(n=1,1e4,if(ispseudoprime((n-1)<Charles R Greathouse IV, Oct 09 2011

Extensions

a(7) corrected by Michael S. Branicky, May 14 2025