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 A242337 #27 Mar 22 2023 08:13:59 %S A242337 4,5,6,7,9,10,11,12,13,14,15,18,22,23,25,32,35,38,45,51,54,57,68,72, %T A242337 82,97,110,138,155,234,254 %N A242337 Numbers k such that k*6^k - 1 is semiprime. %C A242337 The semiprimes of this form are 5183, 38879, 279935, 1959551, 90699263, 604661759, 3990767615, 26121388031, 169789022207, 1097098297343, ... %C A242337 a(32) >= 423. - _Tyler Busby_, Mar 19 2023 %H A242337 factordb.com, <a href="http://factordb.com/index.php?query=6%5E423*423-1">Status of 423*6^423-1</a>. %t A242337 Select[Range[352], PrimeOmega[# 6^# - 1]==2&] %o A242337 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..352] | IsSemiprime(s) where s is n*6^n-1]; %Y A242337 Cf. similar sequences listed in A242273. %Y A242337 Cf. A059675, A064752. %K A242337 nonn,more %O A242337 1,1 %A A242337 _Vincenzo Librandi_, May 12 2014 %E A242337 a(26)-a(31) from _Carl Schildkraut_, Aug 17 2015