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 A203945 #7 Jul 12 2012 00:39:54
%S A203945 1,0,0,0,1,0,1,0,0,1,0,0,1,0,0,0,1,0,0,1,0,1,0,0,2,0,0,1,0,0,1,0,0,1,
%T A203945 0,0,0,1,0,0,2,0,0,1,0,1,0,0,2,0,0,2,0,0,1,0,0,1,0,0,2,0,0,1,0,0,0,1,
%U A203945 0,0,2,0,0,2,0,0,1,0,1,0,0,2,0,0,3,0,0,2,0,0,1,0,0,1,0,0,2,0,0
%N A203945 Symmetric matrix based on (1,0,0,1,0,0,1,0,0,...), by antidiagonals.
%C A203945 Let s be the periodic sequence (1,0,0,1,0,0,...) and let T be the infinite square matrix whose n-th row is formed by putting n-1 zeros before the terms of s. Let T' be the transpose of T. Then A203945 represents the matrix product M=T'*T. M is the self-fusion matrix of s, as defined at A193722. See A203946 for characteristic polynomials of principal submatrices of M, with interlacing zeros.
%e A203945 Northwest corner:
%e A203945 1...0...0...1...0...0...1
%e A203945 0...1...0...0...1...0...0
%e A203945 0...0...1...0...0...1...0
%e A203945 1...0...0...2...0...0...2
%e A203945 0...1...0...0...2...0...0
%t A203945 t = {1, 0, 0}; t1 = Flatten[{t, t, t, t, t, t, t, t}];
%t A203945 s[k_] := t1[[k]];
%t A203945 U = NestList[Most[Prepend[#, 0]] &, #, Length[#] - 1] &[
%t A203945 Table[s[k], {k, 1, 15}]];
%t A203945 L = Transpose[U]; M = L.U; TableForm[M]
%t A203945 m[i_, j_] := M[[i]][[j]];
%t A203945 Flatten[Table[m[i, n + 1 - i], {n, 1, 12}, {i, 1, n}]]
%Y A203945 Cf. A203946, A202453.
%K A203945 nonn,tabl
%O A203945 1,25
%A A203945 _Clark Kimberling_, Jan 08 2012