OFFSET
1,1
COMMENTS
A185755(n,k) equals the coefficient of x^n*y^k in the n-th iteration of x*(1+xy)/(1-x).
PROG
(PARI) {a(n)=local(A=x, G=x*(1+x*y)/(1-x)); for(i=1, n+2, A=subst(G, x, A+O(x^(n+3)))); polcoeff(polcoeff(A, n+2, x), 2, y)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Feb 03 2011
STATUS
approved