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 A121420 #3 Mar 30 2012 18:36:58
%S A121420 1,3,1,12,3,1,76,15,3,1,711,118,18,3,1,9054,1317,169,21,3,1,147471,
%T A121420 19311,2190,229,24,3,1,2938176,352636,36360,3378,298,27,3,1,69328365,
%U A121420 7722840,737051,62655,4929,376,30,3,1,1891371807,197354133,17645187
%N A121420 Matrix cube of triangle A121412.
%C A121420 Row n of triangle T=A121412 equals row (n-1) of T^(n+1) with an appended '1'.
%e A121420 Triangle begins:
%e A121420 1;
%e A121420 3, 1;
%e A121420 12, 3, 1;
%e A121420 76, 15, 3, 1;
%e A121420 711, 118, 18, 3, 1;
%e A121420 9054, 1317, 169, 21, 3, 1;
%e A121420 147471, 19311, 2190, 229, 24, 3, 1;
%e A121420 2938176, 352636, 36360, 3378, 298, 27, 3, 1;
%e A121420 69328365, 7722840, 737051, 62655, 4929, 376, 30, 3, 1; ...
%o A121420 (PARI) {T(n, k)=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^3)[n+1, k+1])}
%Y A121420 Cf. A121412, A121416; A101479; columns: A121421, A121422, A121423.
%K A121420 nonn,tabl
%O A121420 0,2
%A A121420 _Paul D. Hanna_, Aug 23 2006