This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A120922 #3 Mar 30 2012 18:36:58
%S A120922 1,3,18,128,876,6138,43373,307857,2194731,15698743,112614054,
%T A120922 809905638,5838361138,42178611879,305340946455,2214760026120,
%U A120922 16094665727934,117171115942752,854506665035841,6242259681316251,45674776431331398
%N A120922 Main diagonal of triangle A120919 (cascadence of (1+x)^3); a(n) = A120919(n,n) for n>=0.
%o A120922 (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)}
%Y A120922 Cf. A120919, A120920, A120921, A120923.
%K A120922 nonn
%O A120922 0,2
%A A120922 _Paul D. Hanna_, Jul 17 2006