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 A121419 #3 Mar 30 2012 18:36:58
%S A121419 1,2,11,101,1305,21745,443329,10679494,296547736,9319259500,
%T A121419 326788327650,12643827604842,534889691765631,24555735428777265,
%U A121419 1215611513578215355,64542477563559758310,3658333757447085090365
%N A121419 Column 2 of triangle A121416.
%C A121419 A121416 is the matrix square of triangle A121412; row n of triangle T=A121412 equals row (n-1) of T^(n+1) with an appended '1'.
%o A121419 (PARI) {a(n)=local(A=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]=(A^i)[i-1, j]); )); A=B); return((A^2)[n+3, 3])}
%Y A121419 Cf. A121416 (triangle); other columns: A121417, A121418.
%K A121419 nonn
%O A121419 0,2
%A A121419 _Paul D. Hanna_, Aug 22 2006