OFFSET
0,2
FORMULA
E.g.f.: B(x)^2, where B(x) is the e.g.f. of A375796.
a(n) = n! * Sum_{k=0..floor(n/3)} (n-3*k+1)! * Stirling2(n-2*k,n-3*k)/(n-2*k)!.
PROG
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(1/(1-(exp(x^3)-1)/x^2)^2))
(PARI) a(n) = n!*sum(k=0, n\3, (n-3*k+1)!*stirling(n-2*k, n-3*k, 2)/(n-2*k)!);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Aug 29 2024
STATUS
approved