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 A121429 #3 Mar 30 2012 18:36:58
%S A121429 1,2,18,250,4520,99351,2556806,75190410,2483617140,90955908010,
%T A121429 3655774038653,159938142409890,7564604603286913,384576889110665055,
%U A121429 20912407157570989950,1211142337261176799610,74427504634177621877538
%N A121429 Main diagonal of rectangular table A121428.
%F A121429 a(n) = [A121412^(n+1)](n+2,2) for n>=0; i.e., the (n+1)-th term of column 2 in matrix power A121412^(n+1).
%o A121429 (PARI) {a(n)=local(H=Mat(1), B); for(m=1, n+3, B=matrix(m, m); for(i=1, m, for(j=1, i, if(j==i, B[i, j]=1, B[i, j]=(H^i)[i-1, j]); )); H=B); return((H^(n+1))[n+3, 3])}
%Y A121429 Cf. A121428, A121412.
%K A121429 nonn
%O A121429 0,2
%A A121429 _Paul D. Hanna_, Aug 26 2006