A181491 Primes of the form p = 3*2^k - 1 such that p+2 is also prime.

5, 11, 191, 786431

Offset

1,1

Comments

Sequence A181490 lists the exponents k, sequences A181492 and A181493 the corresponding upper twin prime and their average.

a(5) > 3 * 2 ^ 3000 + 1. - Max Z. Scialabba, Dec 24 2023

Links

Table of n, a(n) for n=1..4.

Formula

A181491 = A007283 intersect A014574 = A181492 - 2 = A181493 - 1 = 3*2^A153890 - 1.

Prog

(PARI) for( k=1, 999, ispseudoprime(3<<k-1)|next; ispseudoprime(3<<k+1)|next; print1(3<<k-1, ", "))

Crossrefs

Cf. A001097, A001359, A006512, A014574.

Sequence in context: A179388 A336623 A229907 * A006572 A184934 A159009

Adjacent sequences: A181488 A181489 A181490 * A181492 A181493 A181494

Keyword

bref,nonn

Author

M. F. Hasler, Oct 30 2010

Status

approved