A123214 Primes q such that (2^p + 1)/3 is prime, where p = Prime[q]; or primes in A123176[n].

2, 3, 5, 7, 11, 31, 43, 1697, 12923, 13103, 77509

Offset: 1

Author

Alexander Adamchuk, Oct 05 2006

Keywords

• hard
• more
• nonn

Comments

A123176[n] are the numbers n such that (2^p + 1)/3 is prime, where p = Prime[n]. A123176[n] = PrimePi[A000978[n]]. PrimePi[a(n)] = {1,2,3,4,5,11,14,265,1540,1559,...}.

Examples

			A123176[n] begin {2, 3, 4, 5, 6, 7, 8, 9, 11, 14, 18, 22, 26, 31, 39, 43, ...}.
Thus
a(1) = 2, a(2) = 3, a(3) = 5, a(4) = 7, a(5) = 11, a(6) = 31, a(7) = 43.
		

Crossrefs

Cf. A123176, A000978, A000979, A001045, A049883, A107036.

Extensions

One more term from Max Alekseyev, Feb 06 2010