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 A242269 #24 Sep 08 2022 08:46:08 %S A242269 3,5,11,12,18,20,21,24,25,35,43,45,53,58,61,71,73,75,123,124,140,147, %T A242269 157,205,208,233,243,245,293,301 %N A242269 Numbers n such that n*6^n+1 is semiprime. %C A242269 The semiprimes of this form are: 649, 38881, 3990767617, 26121388033, 1828079220031489, 73123168801259521, 460675963447934977,... %C A242269 464 is definitely in this sequence, however 436 may or may not be. - _Carl Schildkraut_, Aug 28 2015 %C A242269 A continuation in the range 302 ... 1000 would use all terms without "?" and potentially ?-marked terms corresponding to composites with unknown factorization: 436?, 464, 511?, 512, 613, 662?, 720, 730, 802?, 865?, 943. - _Hugo Pfoertner_, Aug 05 2019 %H A242269 factordb.com, <a href="http://factordb.com/index.php?query=436*6%5E436%2B1">Status of 436*6^436+1</a>. %t A242269 Select[Range[435], PrimeOmega[# 6^# + 1] == 2 &] %o A242269 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [1..435] | IsSemiprime(s) where s is n*6^n+1]; %o A242269 (PARI) is(n)=bigomega(n*6^n+1)==2 \\ _Anders Hellström_, Aug 28 2015 %Y A242269 Cf. similar sequences listed in A242203. %Y A242269 Cf. A050917, A242176. %K A242269 nonn,more,hard %O A242269 1,1 %A A242269 _Vincenzo Librandi_, May 10 2014 %E A242269 a(19)-a(30) from _Carl Schildkraut_, Aug 28 2015