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 A138083 #9 Jul 09 2025 23:32:17 %S A138083 0,1,2,4,5,6 %N A138083 Numbers k such that (3^(2^k) + 1)/2 is prime. %C A138083 See A171381, which is the main entry for this sequence. %o A138083 (PARI) is(n)=ispseudoprime((3^(2^n)+1)/2) \\ _Charles R Greathouse IV_, Jun 06 2017 %Y A138083 Cf. A093625, A171381. %K A138083 nonn,more,hard %O A138083 1,3 %A A138083 _N. J. A. Sloane_, Dec 09 2009