A268645 - OEIS

%I #9 Jul 18 2022 09:58:53

%S 1,2,3,6,8,15,24,48,105,120,384,720,945,3840,5040,10395,40320,46080,

%T 135135,362880,645120,2027025,3628800,10321920,34459425,39916800,

%U 185794560,479001600,654729075,3715891200,6227020800,13749310575,81749606400,87178291200,316234143225,1307674368000

%N Union of the factorial numbers (A000142) and the double factorials numbers (A006882).

%D Douglas Hoftstadter, Keynote lecture, DIMACS Workshop on Recognition of Integer Sequences, Oct. 10, 2014.

%H <a href="http://dimacs.rutgers.edu/Workshops/OEIS/abstracts.html#hofstadter">Abstract of D. Hoftstadter in the Workshop's program</a>

%t max = 10^13;

%t A000142 = Reap[For[k = 0, k!  <= max, k++, Sow[k!]]][[2, 1]];

%t A006882 = Reap[For[k = 0, k!! <= max, k++, Sow[k!!]]][[2, 1]];

%t Union[A000142, A006882] (* _Jean-François Alcover_, Jul 18 2022 *)

%Y Cf. A000142, A006882.

%Y See A248652 for another version.

%K nonn

%O 1,2

%A _Olivier Gérard_, Oct 10 2014, revised by _N. J. A. Sloane_, Feb 09 2016