A175172 Primes p such that 3*2^p+1 is also prime.

2, 5, 41, 353

Offset: 1

Author

Vincenzo Librandi, Mar 09 2010

Keywords

• nonn
• hard
• more

Comments

If it exists, a(5) > 250000. - Hugo Pfoertner, Apr 12 2025

Examples

			For p=2, 3*2^2+1=13; p=5. 3*2^5+1=97; p=41, 3*2^41+1=6597069766657.
		

Crossrefs

Cf. A000040, A002253.

Programs

Magma

[p: p in PrimesUpTo(4000) | IsPrime(3*2^p+1)];

Maple

select(p->isprime(p) and isprime(3*2^p+1),[$0..5000]); # Muniru A Asiru, Dec 19 2018

Mathematica

Select[Prime[Range[1000]], PrimeQ[3 2^# + 1] &] (* Vincenzo Librandi, Dec 19 2018 *)

Formula

A000040 INTERSECT A002253. - R. J. Mathar, Jan 04 2011