OFFSET
0,5
FORMULA
a(n)=n!*sum(m=1..n, sum(k=m..n, (stirling2(k,m)*binomial(k,n-2*k)*3^(2*k-n)*2^(-k))/k!)), n>0, a(0)=1.
PROG
(Maxima)
a(n):=n!*sum(sum((stirling2(k, m)*binomial(k, n-2*k)*3^(2*k-n)*2^(-k))/k!, k, m, n), m, 1, n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Kruchinin, Jun 05 2011
STATUS
approved