A248652 Union of the factorial numbers (A000142) and the double factorials of odd numbers (A001147).

1, 2, 3, 6, 15, 24, 105, 120, 720, 945, 5040, 10395, 40320, 135135, 362880, 2027025, 3628800, 34459425, 39916800, 479001600, 654729075, 6227020800, 13749310575, 87178291200, 316234143225, 1307674368000, 7905853580625, 20922789888000, 213458046676875, 355687428096000

Offset: 1

Author

Olivier Gérard, Oct 10 2014

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, A001147, A005214.

See A268645 for another version.

Programs

Mathematica

max = 10^15;
A000142 = Reap[For[k = 0, k!  <= max, k++, Sow[k!]]][[2, 1]];
A001147 = Reap[For[k = 1, k!! <= max, k = k+2, Sow[k!!]]][[2, 1]];
Union[A000142, A001147] (* Jean-François Alcover, Jul 18 2022 *)

Extensions

Revised by N. J. A. Sloane, Feb 09 2016