A356012 a(n) = n! / (6 * floor(n/3)).

1, 4, 20, 60, 420, 3360, 20160, 201600, 2217600, 19958400, 259459200, 3632428800, 43589145600, 697426329600, 11856247603200, 177843714048000, 3379030566912000, 67580611338240000, 1216451004088320000, 26761922089943040000, 615524208068689920000

Offset

3,2

Links

Table of n, a(n) for n=3..23.

Formula

E.g.f.: -(1 - x^3) * log(1 - x^3)/(6 * (1 - x)).

Mathematica

Table[n!/(6 Floor[n/3]), {n, 3, 30}] (* Harvey P. Dale, Jul 25 2024 *)

Prog

(PARI) a(n) = n!/(6*(n\3));
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(-(1-x^3)*log(1-x^3)/(6*(1-x))))

Crossrefs

Column 3 of A356013.

Cf. A355990.

Sequence in context: A197404 A355990 A169637 * A169638 A226424 A225260

Adjacent sequences: A356009 A356010 A356011 * A356013 A356014 A356015

Keyword

nonn,easy

Author

Seiichi Manyama, Jul 23 2022

Status

approved