OFFSET
0,2
COMMENTS
A001858 enumerates forests of labeled trees with n nodes and shifts 1 place left under the hyperbinomial transform.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..385
FORMULA
a(n) = Sum_{k=0..n} 3*(n-k+3)^(n-k-1)*C(n, k)*A001858(k).
a(n) = Sum_{m=0..(n+1)} ( Sum_{j=0..m} C(m, j)*C(n, n-m-j+1)*(n+3)^(n-m-j+1)*(m+j)!/(-2)^j )/m!.
a(n) ~ 3 * exp(7/2) * n^(n-1). - Vaclav Kotesovec, Oct 11 2020
MATHEMATICA
Table[Sum[Sum[Binomial[m, j]*Binomial[n, n - m - j + 1]*(n + 3)^(n - m - j + 1)*(m + j)!/(-2)^j, {j, 0, m}]/m!, {m, 0, n + 1}], {n, 0, 50}] (* G. C. Greubel, Nov 18 2017 *)
PROG
(PARI) a(n)=if(n<0, 0, sum(m=0, n+1, sum(j=0, m, binomial(m, j)*binomial(n, n-m-j+1)*(n+3)^(n-m-j+1)*(m+j)!/(-2)^j)/m!))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 05 2003
STATUS
approved