OFFSET
0,2
COMMENTS
EXAMPLE
G.f.: A(x) = 1 + 2*x + 15*x^2 + 234*x^3 + 6019*x^4 + 226656*x^5 +...
Note that the square-root of the g.f., A(x)^(1/2), is an integer series:
A(x)^(1/2) = 1 + x + 7*x^2 + 110*x^3 + 2875*x^4 + 109683*x^5 +...+ A212371(n)*x^n +...
PROG
(PARI) {a(n)=if(n==0, 1, -polcoeff(sum(m=0, n-1, a(m)*x^m*sum(k=0, m+1, binomial(m+1, k)^2*(-x)^k)^2+x*O(x^n)), n))}
for(n=0, 20, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, May 10 2012
STATUS
approved