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 A242340 #13 Sep 08 2022 08:46:08 %S A242340 2,3,6,8,11,18,28,38,48,168,254,274,310,430 %N A242340 Numbers k such that k*9^k-1 is semiprime. %C A242340 The semiprimes of this form are: 161, 2186, 3188645, 344373767, 345191655698, 2701703435345984177, 14653733724766095041978322587, ... %C A242340 a(15) >= 512. - _Daniel Suteu_, Aug 05 2019 %t A242340 Select[Range[70], PrimeOmega[# 9^# - 1]==2&] %o A242340 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..70] | IsSemiprime(s) where s is n*9^n-1]; %Y A242340 Cf. similar sequences listed in A242273. %Y A242340 Cf. A064755, A242202. %K A242340 nonn,more %O A242340 1,1 %A A242340 _Vincenzo Librandi_, May 12 2014 %E A242340 a(10)-a(14) from _Daniel Suteu_, Aug 05 2019