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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
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
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
KEYWORD
nonn
AUTHOR
M. F. Hasler, Oct 30 2010
STATUS
approved