%I #19 Jan 21 2024 09:25:30
%S 5,11,191,786431
%N Primes of the form p = 3*2^k - 1 such that p+2 is also prime.
%C Sequence A181490 lists the exponents k, sequences A181492 and A181493 the corresponding upper twin prime and their average.
%C a(5) > 3 * 2 ^ 3000 + 1. - _Max Z. Scialabba_, Dec 24 2023
%F A181491 = A007283 intersect A014574 = A181492 - 2 = A181493 - 1 = 3*2^A153890 - 1.
%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 bref,nonn
%O 1,1
%A _M. F. Hasler_, Oct 30 2010