A172461 Primes p such that 2*p-1 and 2^p-1 are both primes.

2, 3, 7, 19, 31, 607, 1279, 2281, 44497, 1257787, 13466917

Offset: 1

Author

Juri-Stepan Gerasimov, Feb 03 2010, Feb 06 2010

Keywords

• nonn
• more

Examples

			a(1) = 2 is a term since it is a prime and 2^2 - 1 = 3 and 2*2 - 1 = 3 are primes.
a(2) = 3 is a term since it is a prime and 2^3 - 1 = 7 and 2*3 - 1 = 5 are primes.
		

Crossrefs

Intersection of A000043 and A005382.

Cf. A000668.

Programs

Mathematica

Select[MersennePrimeExponent[Range[47]], PrimeQ[2# -1] &] (* Amiram Eldar, Jul 29 2020 *)

Extensions

a(9)-a(11) from Robert G. Wilson v, Feb 26 2010