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 A242272 #14 Sep 08 2022 08:46:08 %S A242272 1,8,12,16,20,50,208,254,282,342,350,386 %N A242272 Numbers n such that n*9^n+1 is semiprime. %C A242272 The semiprimes of this form are: 10, 344373769, 3389154437773, 29648323021629457, 243153309181138576021, ... %C A242272 a(13) >= 512. - _Hugo Pfoertner_, Aug 05 2019 %H A242272 factordb.com, <a href="http://factordb.com/index.php?query=9%5E512*512%2B1">Status of 512*9^512+1</a>. %t A242272 Select[Range[70], PrimeOmega[# 9^# + 1] == 2 &] %o A242272 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [1..70] | IsSemiprime(s) where s is n*9^n+1]; %Y A242272 Cf. similar sequences listed in A242203. %Y A242272 Cf. A064747. %K A242272 nonn,more,hard %O A242272 1,2 %A A242272 _Vincenzo Librandi_, May 10 2014 %E A242272 a(7)-a(12) from _Hugo Pfoertner_, Aug 05 2019