A185758 A diagonal of triangle A185755.

2, 15, 120, 1190, 14595, 215950, 3761310, 75550188, 1721103648, 43872089118, 1237592664451, 38282002057156, 1288537309627464, 46886217384094764, 1834003542264708444, 76744318019878844916, 3420833746251201921980

Offset: 1

Author

Paul D. Hanna, Feb 03 2011

Keywords

• nonn

Comments

A185755(n,k) equals the coefficient of x^n*y^k in the n-th iteration of x*(1+xy)/(1-x).

Crossrefs

Cf. A185755, A185756, A185757, A185759.

Programs

PARI

{a(n)=local(A=x, G=x*(1+x*y)/(1-x)); for(i=1, n+1, A=subst(G, x, A+O(x^(n+2))));polcoeff(polcoeff(A, n+1,x),n-1,y)}