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 A259026 #46 Sep 08 2022 08:46:13 %S A259026 1,2,6,8,18,21,24,26,28,30,33,230 %N A259026 Numbers n such that n*23^n-1 is semiprime. %C A259026 After 290, which may or may not be in the sequence, 420 and 450 are definitely in the sequence. %H A259026 K. O'Bryant, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL18/OBryant/obr3.html">Sets of Natural Numbers with Proscribed Subsets</a>, J. Int. Seq. 18 (2015) # 15.7.7 %t A259026 Select[Range[200], PrimeOmega[# 23^# - 1]==2&] %o A259026 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..200] | IsSemiprime(s) where s is n*23^n-1]; %o A259026 (PARI) isok(n)=bigomega(n*23^n-1)==2 \\ _Anders Hellström_, Aug 20 2015 %Y A259026 Similar sequences listed in A242273. %K A259026 nonn,more %O A259026 1,2 %A A259026 _Luke March_, Aug 06 2015