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A355990 revision #16

A355990

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

1, 4, 20, 60, 420, 3360, 10080, 100800, 1108800, 3326400, 43243200, 605404800, 1816214400, 29059430400, 494010316800, 1482030950400, 28158588057600, 563171761152000, 1689515283456000, 37169336236032000, 854894733428736000, 2564684200286208000

(list; graph; refs; listen; history; text; internal format)

OFFSET

3,2

LINKS

Table of n, a(n) for n=3..24.

FORMULA

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

a(n) = A355988(n)/6.

MATHEMATICA

a[n_] := n!/(6 * Floor[n/3]!); Array[a, 22, 3] (* Amiram Eldar, Jul 22 2022 *)

PROG

(PARI) a(n) = n!/(6*(n\3)!);