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 A248652 #19 Jul 18 2022 09:49:51 %S A248652 1,2,3,6,15,24,105,120,720,945,5040,10395,40320,135135,362880,2027025, %T A248652 3628800,34459425,39916800,479001600,654729075,6227020800,13749310575, %U A248652 87178291200,316234143225,1307674368000,7905853580625,20922789888000,213458046676875,355687428096000 %N A248652 Union of the factorial numbers (A000142) and the double factorials of odd numbers (A001147). %D A248652 Douglas Hoftstadter, Keynote lecture, DIMACS Workshop on Recognition of Integer Sequences, Oct. 10, 2014. %H A248652 <a href="http://dimacs.rutgers.edu/Workshops/OEIS/abstracts.html#hofstadter">Abstract of D. Hoftstadter in the Workshop's program</a> %t A248652 max = 10^15; %t A248652 A000142 = Reap[For[k = 0, k! <= max, k++, Sow[k!]]][[2, 1]]; %t A248652 A001147 = Reap[For[k = 1, k!! <= max, k = k+2, Sow[k!!]]][[2, 1]]; %t A248652 Union[A000142, A001147] (* _Jean-François Alcover_, Jul 18 2022 *) %Y A248652 Cf. A000142, A001147, A005214. %Y A248652 See A268645 for another version. %K A248652 nonn %O A248652 1,2 %A A248652 _Olivier Gérard_, Oct 10 2014 %E A248652 Revised by _N. J. A. Sloane_, Feb 09 2016