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A120922
Main diagonal of triangle A120919 (cascadence of (1+x)^3); a(n) = A120919(n,n) for n>=0.
3
1, 3, 18, 128, 876, 6138, 43373, 307857, 2194731, 15698743, 112614054, 809905638, 5838361138, 42178611879, 305340946455, 2214760026120, 16094665727934, 117171115942752, 854506665035841, 6242259681316251, 45674776431331398
OFFSET
0,2
PROG
(PARI) {a(n)=local(A, F=(1+x)^3, d=3, 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)}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Jul 17 2006
STATUS
approved