OFFSET
1,2
FORMULA
EXAMPLE
E.g.f.: x + 3*x^2 + 15*x^3/2! + 102*x^4/3! + 861*x^5/4! +...
PROG
(PARI) {a(n)=local(F=x, xEx=x*exp(x+x*O(x^n))); for(i=1, 3, F=subst(F, x, xEx)); (n-1)!*polcoeff(F, n)}
(PARI) {a(n)=sum(k=0, n-1, binomial(n-1, k)*sum(j=0, n-1-k, binomial(n-1-k, j)*(k+1)^j*(k+1+j)^(n-1-k-j)))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Apr 17 2010
STATUS
approved