OFFSET
0,3
FORMULA
E.g.f.: (1/x) * Series_Reversion( x*exp(-x * (1 + x^2)) ).
a(n) = n! * Sum_{k=0..floor(n/3)} (n+1)^(n-2*k-1) * binomial(n-2*k,k)/(n-2*k)!.
PROG
(PARI) a(n) = n!*sum(k=0, n\3, (n+1)^(n-2*k-1)*binomial(n-2*k, k)/(n-2*k)!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Sep 28 2024
STATUS
approved