OFFSET
0,3
FORMULA
G.f.: A(x) = 1 + A(x/(1-x))^2*x/(1-x).
PROG
(PARI) {a(n)=local(A); if(n<0, 0, A=1+x+x*O(x^n); for(k=1, n, B=subst(A^2, x, x/(1-x))/(1-x)+x*O(x^n); A=1+x*B); polcoeff(A, n, x))}
(Maxima) a(n):=if n=0 then 1 else sum(binomial(n-1, k-1)*sum(a(k-1-i)*a(i), i, 0, k-1), k, 1, n); /* Vladimir Kruchinin, Jun 25 2011 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 26 2003
STATUS
approved