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 A363837 #18 Feb 16 2025 08:34:05 %S A363837 6,8,10,14,26,29,34,37,38,41,47,49,53,62,67,71,73,103,107,109,122,139, %T A363837 151,179,223,229,251,254,269,277,311,349,353,433,457,487,503,599,601, %U A363837 613,619,643,739,757,827,839,1031,1061,1117 %N A363837 Numbers k such that k-th Jacobsthal number A001045(k) is a semiprime. %H A363837 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/JacobsthalNumber.html">Jacobsthal Number</a>. %H A363837 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Semiprime.html">Semiprime</a>. %e A363837 10 is a term because Jacobsthal(10) = A001045(10) = 341 = 11*31 is a semiprime. %o A363837 (PARI) isok(k) = bigomega((2^k - (-1)^k)/3) == 2; \\ _Michel Marcus_, Oct 19 2023 %Y A363837 Cf. A001045, A001358, A277356 (the actual semiprimes), A250292, A085726, A072381, A101757, A286567, A271314. %K A363837 nonn,more %O A363837 1,1 %A A363837 _Sean A. Irvine_, Oct 19 2023 %E A363837 a(47)-a(49) from _Amiram Eldar_, Feb 25 2024