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 A252658 #26 Sep 08 2022 08:46:10 %S A252658 1,3,8,14,18,48,52,54,62,72,96,98,114,186,486,524,712 %N A252658 Numbers m such that 5^m - m is a semiprime. %C A252658 There are no other known terms under 1000 - the only possible terms are 812 and 908. - _Carl Schildkraut_, Aug 21 2015 %e A252658 1 is in this sequence because 5^1-1 = 2*2 is semiprime. %e A252658 18 is in this sequence because 5^18-18 = 199*19169332993 and these two factors are prime. %t A252658 Select[Range[100], PrimeOmega[5^# - #]==2 &] %o A252658 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..100] | IsSemiprime(s) where s is 5^m-m]; %o A252658 (PARI) isok(n)=bigomega(5^n - n)==2 \\ _Anders Hellström_, Aug 21 2015 %Y A252658 Cf. similar sequences listed in A252656. %K A252658 nonn,more %O A252658 1,2 %A A252658 _Vincenzo Librandi_, Dec 20 2014 %E A252658 a(13)-a(17) from _Carl Schildkraut_, Aug 21 2015