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%I #21 Jan 21 2024 09:20:11
%S 7,13,193,786433
%N Primes of the form p=3*2^k+1 such that p-2 is also a prime.
%C Sequence A181490 lists the exponents k, sequences A181491 and A181493 the corresponding lesser twin prime and their average.
%C a(5) > 3 * 2^3000 + 1. - _Max Z. Scialabba_, Dec 24 2023
%F A181492 = A181491 + 2 = A181493 + 1 = 3*2^A181490 + 1 = intersection of A004119 or A103204 or A181495 with A006512 or A001097.
%t Select[3 2^Range[100]+1,And@@PrimeQ[{#,#-2}]&] (* _Harvey P. Dale_, Jun 19 2013 *)
%o (PARI) for( k=1,999, ispseudoprime(3<<k-1)|next; ispseudoprime(3<<k+1)|next; print1(3<<k+1,", "))
%Y Cf. A001097, A001359, A006512, A014574.
%K nonn
%O 1,1
%A _M. F. Hasler_, Oct 30 2010
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