A181492 Primes of the form p=3*2^k+1 such that p-2 is also a prime.

7, 13, 193, 786433

Offset

1,1

Comments

Sequence A181490 lists the exponents k, sequences A181491 and A181493 the corresponding lesser 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

A181492 = A181491 + 2 = A181493 + 1 = 3*2^A181490 + 1 = intersection of A004119 or A103204 or A181495 with A006512 or A001097.

Mathematica

Select[3 2^Range[100]+1, And@@PrimeQ[{#, #-2}]&] (* Harvey P. Dale, Jun 19 2013 *)

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: A319612 A247946 A210465 * A243368 A317209 A084963

Adjacent sequences: A181489 A181490 A181491 * A181493 A181494 A181495

Keyword

nonn

Author

M. F. Hasler, Oct 30 2010

Status

approved