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 A268139 #7 Sep 08 2022 08:46:15
%S A268139 6,35,341,2159,6160337,27787211,191126044583,412745898649251217229,
%T A268139 162789115166027506149234835193,51436190754860636195130229261336259
%N A268139 Semiprimes of the form 3*n*2^n - 3*n - 2^(2+n) + 4.
%H A268139 Ben Green and Terence Tao, <a href="http://arXiv.org/abs/math/0404188">The primes contain arbitrarily long arithmetic progressions</a>, Annals of Mathematics, 167 (2008), pp. 481-547. arXiv:math/0404188 [math.NT], 2004-2007.
%t A268139 Select[Table[3 n 2^n - 3 n - 2^(2 + n) + 4, {n, 250}], PrimeOmega[#] == 2 &]
%o A268139 (Magma) IsSemiprime:= func<n | &+[d[2]: d in Factorization(n)] eq 2>; [s: n in [2..240] | IsSemiprime(s) where s is 3*n*2^n-3*n-2^(2+n)+4];
%Y A268139 Cf. A000043, A001348, A228121, A247147.
%K A268139 nonn
%O A268139 1,1
%A A268139 _Vincenzo Librandi_, Jan 27 2016