login
Central terms of triangle A120914 (cascadence of (1+2x)^2).
3

%I #3 Mar 30 2012 18:36:58

%S 1,4,32,212,1504,10848,79696,596160,4520000,34673940,268538048,

%T 2096374656,16475970896,130234435648,1034568731408,8254368150320,

%U 66112337392256,531345216883584,4283682906179728,34632004320564416

%N Central terms of triangle A120914 (cascadence of (1+2x)^2).

%o (PARI) {a(n)=local(A,F=1+4*x+4*x^2,d=2,G=x,H=1+x,S=ceil(log(n+1)/log(d+1))); for(i=0,n,G=x*subst(F,x,G+x*O(x^n)));for(i=0,S,H=subst(H,x,x*G^d+x*O(x^n))*G/x); A=(x*H-y*subst(H,x,x*y^d +x*O(x^n)))/(x*subst(F,x,y)-y); polcoeff(polcoeff(A,n,x),n,y)}

%Y Cf. A120914, A120915, A120916, A120918.

%K nonn

%O 0,2

%A _Paul D. Hanna_, Jul 17 2006