A375226 Expansion of e.g.f. exp( (x / (1-x))^3 ) / (1-x)^2.
1, 2, 6, 30, 240, 2520, 30600, 413280, 6168960, 101666880, 1842825600, 36483955200, 782548905600, 18048500870400, 444816333561600, 11656620213638400, 323500679915212800, 9475966585948262400, 292101319958063616000, 9450373008137757696000
Offset: 0
Keywords
Programs
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PARI
my(N=20, x='x+O('x^N)); Vec(serlaplace(exp((x/(1-x))^3)/(1-x)^2)) -
PARI
a(n) = n!*sum(k=0, n\3, binomial(n+1, n-3*k)/k!);
Formula
a(n) = n! * Sum_{k=0..floor(n/3)} binomial(n+1,n-3*k)/k!.