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A181492 Primes of the form p=3*2^k+1 such that p-2 is also a prime. 7
7, 13, 193, 786433 (list; graph; refs; listen; history; text; internal format)
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<<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

more,nonn

AUTHOR

M. F. Hasler, Oct 30 2010

STATUS

approved

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Last modified January 21 05:39 EST 2020. Contains 331104 sequences. (Running on oeis4.)