OFFSET
0,3
FORMULA
a(n)=(sum(m=1..n, sum(k=m..n, (binomial(k,n-k)*stirling1(k-m,m))/(k-m)!)))*n!, n>0, a(0)=1.
MATHEMATICA
With[{nn=20}, CoefficientList[Series[(1+x+x^2)^(x+x^2), {x, 0, nn}], x] Range[0, nn]!] (* Harvey P. Dale, Aug 21 2017 *)
PROG
(Maxima)
a(n):=(sum(sum((binomial(k, n-k)*stirling1(k-m, m))/(k-m)!, k, m, n), m, 1, n))*n!;
CROSSREFS
KEYWORD
sign
AUTHOR
Vladimir Kruchinin, May 31 2011
STATUS
approved