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 A121418 #6 Mar 30 2012 18:36:58
%S A121418 1,2,7,43,403,5188,85569,1725291,41145705,1133047596,35377360292,
%T A121418 1234796503280,47636225803285,2012509471127885,92398547122062997,
%U A121418 4580472438441602301,243822925502110419105,13870297863425823346284
%N A121418 Column 0 of triangle A121416.
%C A121418 Also column 1 of square array A136733.
%C A121418 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 A121418 (PARI) {a(n)=local(A=Mat(1), B); for(m=1, n+1, 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+1, 1])}
%Y A121418 Cf. A121416 (triangle); other columns: A121418, A121419.
%Y A121418 Cf. A136733; A101483, A121421; A121425.
%K A121418 nonn
%O A121418 0,2
%A A121418 _Paul D. Hanna_, Aug 22 2006, Jan 19 2008
%E A121418 Edited by _N. J. A. Sloane_, Oct 30 2008 at the suggestion of R. J. Mathar