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 A242335 #25 Sep 08 2022 08:46:08 %S A242335 10,12,18,24,27,44,47,65,71,82,84,131,134,138,143,155,164,168,197,212, %T A242335 227,243,248,293,302,384,401 %N A242335 Numbers k such that k*4^k-1 is semiprime. %C A242335 The semiprimes of this form are: 10485759, 201326591, 1236950581247, 6755399441055743, 486388759756013567, 13617340432139183023890366463, ... %t A242335 Select[Range[100], PrimeOmega[# 4^# - 1]==2&] %o A242335 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..100] | IsSemiprime(s) where s is n*4^n-1]; %o A242335 (PARI) isok(n)=bigomega(n*4^n-1)==2 \\ _Anders Hellström_, Aug 18 2015 %Y A242335 Cf. similar sequences listed in A242273. %Y A242335 Cf. A060416, A086661. %K A242335 nonn %O A242335 1,1 %A A242335 _Vincenzo Librandi_, May 12 2014 %E A242335 a(12)-a(16) from _Carl Schildkraut_, Aug 18 2015 %E A242335 a(17)-a(27) from _Charles R Greathouse IV_, Aug 18 2015