A268645 Union of the factorial numbers (A000142) and the double factorials numbers (A006882).

1, 2, 3, 6, 8, 15, 24, 48, 105, 120, 384, 720, 945, 3840, 5040, 10395, 40320, 46080, 135135, 362880, 645120, 2027025, 3628800, 10321920, 34459425, 39916800, 185794560, 479001600, 654729075, 3715891200, 6227020800, 13749310575, 81749606400, 87178291200, 316234143225, 1307674368000

Offset: 1

Author

Olivier Gérard, Oct 10 2014, revised by N. J. A. Sloane, Feb 09 2016

Keywords

• nonn

References

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

Links

• Abstract of D. Hoftstadter in the Workshop's program

Crossrefs

Cf. A000142, A006882.

See A248652 for another version.

Programs

Mathematica

max = 10^13;
A000142 = Reap[For[k = 0, k!  <= max, k++, Sow[k!]]][[2, 1]];
A006882 = Reap[For[k = 0, k!! <= max, k++, Sow[k!!]]][[2, 1]];
Union[A000142, A006882] (* Jean-François Alcover, Jul 18 2022 *)