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 A268645 #9 Jul 18 2022 09:58:53 %S A268645 1,2,3,6,8,15,24,48,105,120,384,720,945,3840,5040,10395,40320,46080, %T A268645 135135,362880,645120,2027025,3628800,10321920,34459425,39916800, %U A268645 185794560,479001600,654729075,3715891200,6227020800,13749310575,81749606400,87178291200,316234143225,1307674368000 %N A268645 Union of the factorial numbers (A000142) and the double factorials numbers (A006882). %D A268645 Douglas Hoftstadter, Keynote lecture, DIMACS Workshop on Recognition of Integer Sequences, Oct. 10, 2014. %H A268645 <a href="http://dimacs.rutgers.edu/Workshops/OEIS/abstracts.html#hofstadter">Abstract of D. Hoftstadter in the Workshop's program</a> %t A268645 max = 10^13; %t A268645 A000142 = Reap[For[k = 0, k! <= max, k++, Sow[k!]]][[2, 1]]; %t A268645 A006882 = Reap[For[k = 0, k!! <= max, k++, Sow[k!!]]][[2, 1]]; %t A268645 Union[A000142, A006882] (* _Jean-François Alcover_, Jul 18 2022 *) %Y A268645 Cf. A000142, A006882. %Y A268645 See A248652 for another version. %K A268645 nonn %O A268645 1,2 %A A268645 _Olivier Gérard_, Oct 10 2014, revised by _N. J. A. Sloane_, Feb 09 2016