This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A181491 #22 Aug 06 2025 22:36:27 %S A181491 5,11,191,786431 %N A181491 Primes of the form p = 3*2^k - 1 such that p+2 is also prime. %C A181491 Sequence A181490 lists the exponents k, sequences A181492 and A181493 the corresponding upper twin prime and their average. %C A181491 a(5) > 3 * 2 ^ 3000 + 1. - _Max Z. Scialabba_, Dec 24 2023 %F A181491 A181491 = A007283 intersect A014574 = A181492 - 2 = A181493 - 1 = 3*2^A153890 - 1. %o A181491 (PARI) for( k=1,999, ispseudoprime(3<<k-1)||next; ispseudoprime(3<<k+1)||next; print1(3<<k-1,", ")) %Y A181491 Cf. A001097, A001359, A006512, A014574. %K A181491 bref,nonn %O A181491 1,1 %A A181491 _M. F. Hasler_, Oct 30 2010