OFFSET
0,5
FORMULA
E.g.f.: ( (1/x) * Series_Reversion( x / (exp(-x) + x)^3 ) )^(1/3).
a(n) = -n! * Sum_{k=0..n} (-3*n+k-1)^(n-k-1) * binomial(3*n,k)/(n-k)!.
PROG
(PARI) a(n) = -n!*sum(k=0, n, (-3*n+k-1)^(n-k-1)*binomial(3*n, k)/(n-k)!);
CROSSREFS
KEYWORD
sign,new
AUTHOR
Seiichi Manyama, Jan 05 2025
STATUS
approved