OFFSET
0,4
FORMULA
a(n)=n!+(n!)^2*(sum(m=1..n-1, sum(k=1..n-m, (k!*stirling1(m+k,m)*stirling2(n-m,k))/(m+k)!)/(n-m)!)), n>0, a(0)=1.
PROG
(Maxima)
a(n):=(n)!+(n!)^2*(sum(sum((k!*stirling1(m+k, m)*stirling2(n-m, k))/(m+k)!, k, 1, n-m)/(n-m)!, m, 1, n-1));
CROSSREFS
KEYWORD
sign
AUTHOR
Vladimir Kruchinin, Jun 06 2011
STATUS
approved