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 A205545 #6 Mar 30 2012 18:58:11
%S A205545 1,1,1,1,1,1,1,20,20,1,1,84,1,84,1,1,220,84,84,220,1,1,455,924,1,924,
%T A205545 455,1,1,816,5005,220,220,5005,816,1,1,1330,18564,5005,1,5005,18564,
%U A205545 1330,1,1,2024,54264,48620,455,455,48620,54264,2024,1,1,2925
%N A205545 Symmetric matrix by antidiagonals: C(max(3i,3j),min(3i,3j)), i>=0, j>=0.
%e A205545 Northwest corner:
%e A205545 1.....20....84....220
%e A205545 20....1.....84....924
%e A205545 84....84....1.....220
%e A205545 455...5005..5005..455
%t A205545 f[i_, j_] := Binomial[Max[3 i - 3, 3 j - 3], Min[3 i - 3, 3 j - 3]]
%t A205545 TableForm[Table[f[i, j], {i, 1, 10}, {j, 1, 10}]]
%t A205545 Flatten[Table[f[i, n + 1 - i], {n, 1, 14}, {i, 1, n}]]
%Y A205545 Cf. A205456.
%K A205545 nonn,tabl
%O A205545 1,8
%A A205545 _Clark Kimberling_, Jan 28 2012