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 A242205 #17 Sep 08 2022 08:46:08 %S A242205 1,2,4,16,21,40,76,113,153,288 %N A242205 Numbers n such that n*5^n+1 is semiprime. %C A242205 The semiprimes of this form are 6, 51, 2501, 2441406250001, 10013580322265626, 363797880709171295166015625001, ... %C A242205 a(11) >= 1006. - _Hugo Pfoertner_, Aug 05 2019 %H A242205 factordb.com, <a href="http://factordb.com/index.php?query=5%5E1006*1006%2B1">Status of 1006*5^1006+1</a>. %t A242205 Select[Range[90], PrimeOmega[# 5^# + 1] == 2 &] %o A242205 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [1..90] | IsSemiprime(s) where s is n*5^n+1]; %Y A242205 Cf. similar sequences listed in A242203. %Y A242205 Cf. A050916. %K A242205 nonn,more,hard %O A242205 1,2 %A A242205 _Vincenzo Librandi_, May 10 2014 %E A242205 a(8)-a(10) from _Luke March_, Aug 13 2015