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
Programs
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Mathematica
a[n_] := n!/Floor[n/3]!; Array[a, 24, 0] (* Amiram Eldar, Jul 22 2022 *)
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PARI
a(n) = n!/(n\3)!;
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PARI
my(N=30, x='x+O('x^N)); Vec(serlaplace((1-x^3)*exp(x^3)/(1-x)))
Formula
E.g.f.: (1 - x^3) * exp(x^3)/(1 - x).