A120917 Central terms of triangle A120914 (cascadence of (1+2x)^2).

1, 4, 32, 212, 1504, 10848, 79696, 596160, 4520000, 34673940, 268538048, 2096374656, 16475970896, 130234435648, 1034568731408, 8254368150320, 66112337392256, 531345216883584, 4283682906179728, 34632004320564416

Offset: 0

Author

Paul D. Hanna, Jul 17 2006

Keywords

• nonn

Crossrefs

Cf. A120914, A120915, A120916, A120918.

Programs

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)}