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 A121413 #3 Mar 30 2012 18:36:58
%S A121413 1,1,4,30,335,4984,92652,2065146,53636520,1589752230,52926799310,
%T A121413 1954793723688,79297921097850,3504206787532290,167533486104374420,
%U A121413 8615231103973721610,474145710046504872894,27806642356199323970739
%N A121413 Column 1 of triangle A121412, in which row n of T equals row (n-1) of T^(n+1) with an appended '1'.
%C A121413 Also equals column 3 of triangle A101479.
%o A121413 (PARI) {a(n)=local(A=Mat(1), B); for(m=1, n+2, 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^1)[n+2, 2])}
%Y A121413 Cf. A121412 (triangle); other columns: A101483, A121414, A121415; A101479 (triangle).
%K A121413 nonn
%O A121413 0,3
%A A121413 _Paul D. Hanna_, Aug 22 2006