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 A252663 #22 Sep 08 2022 08:46:10 %S A252663 1,7,9,11,15,33,77,93,107,117,143,149,177,209,221 %N A252663 Numbers m such that 10^m - m is a semiprime. %C A252663 a(16) >= 269. - _Hugo Pfoertner_, Aug 04 2019 %H A252663 factorbd.com, <a href="http://factordb.com/index.php?query=10%5E269-269">Status of 10^269-269</a>. %e A252663 1 is in this sequence because 10^1-1 = 3*3 is semiprime. %e A252663 9 is in this sequence because 10^9-9 = 67*14925373 and these two factors are prime. %t A252663 Select[Range[80], PrimeOmega[10^# - #]==2 &] %o A252663 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..80] | IsSemiprime(s) where s is 10^m-m]; %o A252663 (PARI) is(m) = bigomega(10^m - m) == 2; \\ _Jinyuan Wang_, Jul 09 2019 %Y A252663 Cf. similar sequences listed in A252656. %K A252663 nonn,more,hard %O A252663 1,2 %A A252663 _Vincenzo Librandi_, Dec 22 2014 %E A252663 a(8) from _Luke March_, Jul 08 2015 %E A252663 a(9)-a(13) from _Daniel Suteu_, Jul 09 2019 %E A252663 a(14), a(15) from _Hugo Pfoertner_, Aug 04 2019