

A181492


Primes of the form p=3*2^k+1 such that p2 is also a prime.


7




OFFSET

1,1


COMMENTS

Sequence A181490 lists the exponents k, sequences A181491 and A181493 the corresponding lesser twin prime and their average.


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<<k1)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

more,nonn


AUTHOR

M. F. Hasler, Oct 30 2010


STATUS

approved



