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 A252657 #31 Sep 08 2022 08:46:10 %S A252657 2,11,17,33,55,59,63,153,315 %N A252657 Numbers m such that 4^m - m is a semiprime. %C A252657 549, 721, and 755 are in the sequence, but not necessarily the next three terms. The other possibilities for a(9) are 483, 503, and 543. - _Robert Israel_, Feb 10 2019 %H A252657 factordb.com, <a href="http://factordb.com/index.php?query=4%5E483-483">Status of 4^483-483</a>. %e A252657 2 is in this sequence because 4^2-2 = 2*7 is semiprime. %e A252657 17 is in this sequence because 4^17-17 = 6971*2464477 and these two factors are prime. %t A252657 Select[Range[120], PrimeOmega[4^# - #]==2 &] %o A252657 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [2..120] | IsSemiprime(s) where s is 4^m-m]; %Y A252657 Cf. A024037 (4^n - n). %Y A252657 Cf. similar sequences listed in A252656. %K A252657 nonn,more %O A252657 1,1 %A A252657 _Vincenzo Librandi_, Dec 20 2014 %E A252657 a(8)-a(9) from _Luke March_, Jul 08 2015