A355988 a(n) = n! / floor(n/3)!.

1, 1, 2, 6, 24, 120, 360, 2520, 20160, 60480, 604800, 6652800, 19958400, 259459200, 3632428800, 10897286400, 174356582400, 2964061900800, 8892185702400, 168951528345600, 3379030566912000, 10137091700736000, 223016017416192000, 5129368400572416000

Offset

0,3

Links

Table of n, a(n) for n=0..23.

Formula

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

Mathematica

a[n_] := n!/Floor[n/3]!; Array[a, 24, 0] (* Amiram Eldar, Jul 22 2022 *)

Prog

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

Crossrefs

Cf. A081125, A355990.

Sequence in context: A364425 A178010 A366368 * A330043 A062348 A189856

Adjacent sequences: A355985 A355986 A355987 * A355989 A355990 A355991

Keyword

nonn,easy

Author

Seiichi Manyama, Jul 22 2022

Status

approved