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 A360994 #39 Mar 03 2023 06:01:27
%S A360994 0,1,2,4,5,6,13,14,18,27,43,45,63,76,85,108,115,119,123,187,211,215,
%T A360994 283,312
%N A360994 Numbers k such that (2^k + 1)^3 - 2 is a semiprime.
%C A360994 a(25) >= 355.
%C A360994 623, 674, 711, 766, 767 are also in this sequence, but their position cannot be established before finding any factor for the values corresponding to the following "blockers": 355, 511, 587, 707, 731.
%C A360994 1424, 1470, 1580, 1946, 2117, 2693, 3000, 3540, 4164, 7043, 9475, 10632, 15018, 19064, 27130, 28266, 28532, 46434, 58768, 103536 are some larger members of this sequence, but their position cannot be established. These produce "trivial" semiprimes where one prime is small (e.g., 3 or 5).
%H A360994 factordb.com, <a href="http://factordb.com/index.php?query=%282%5E355%2B1%29%5E3-2">Status of (2^355+1)^3-2</a>.
%F A360994 { k >= 0 : A099359(k) in { A001358 } }.
%t A360994 Select[Range[70], PrimeOmega[(2^# + 1)^3 - 2] == 2 &]
%o A360994 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [1..70]| IsSemiprime(s) where s is (2^n+1)^3-2];
%o A360994 (PARI) isok(n) = bigomega((2^n+1)^3-2) == 2;
%Y A360994 Cf. A001358, A091513, A091514, A093069, A099359, A100899, A100900, A269264, A360993.
%K A360994 nonn,more,hard
%O A360994 1,3
%A A360994 _Serge Batalov_, Feb 27 2023