A203953 Symmetric matrix based on (1,2,1,2,1,2,...), by antidiagonals.

1, 2, 2, 1, 5, 1, 2, 4, 4, 2, 1, 5, 6, 5, 1, 2, 4, 6, 6, 4, 2, 1, 5, 6, 10, 6, 5, 1, 2, 4, 6, 8, 8, 6, 4, 2, 1, 5, 6, 10, 11, 10, 6, 5, 1, 2, 4, 6, 8, 10, 10, 8, 6, 4, 2, 1, 5, 6, 10, 11, 15, 11, 10, 6, 5, 1, 2, 4, 6, 8, 10, 12, 12, 10, 8, 6, 4, 2, 1, 5, 6, 10, 11, 15, 16, 15, 11, 10

Offset: 1

Author

Clark Kimberling, Jan 08 2012

Keywords

• nonn
• tabl

Comments

Let s be the periodic sequence (1,2,1,2,1,2,...) 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 A203951 represents the matrix product M=T'*T. M is the self-fusion matrix of s, as defined at A193722. See A203954 for characteristic polynomials of principal submatrices of M, with interlacing zeros.

Examples

			Northwest corner:
1 2 1 2 1 2 1
2 5 4 5 4 5 4
1 3 6 6 6 6 6
		

Crossrefs

Cf. A203954, A202453.

Programs

Mathematica

t = {1, 2}; t1 = Flatten[{t, t, t, t, t, t, t, t, t, t}];
s[k_] := t1[[k]];
U = NestList[Most[Prepend[#, 0]] &, #, Length[#] - 1] &[
   Table[s[k], {k, 1, 15}]];
L = Transpose[U]; M = L.U; TableForm[M]  (* A203953 *)
m[i_, j_] := M[[i]][[j]];
Flatten[Table[m[i, n + 1 - i], {n, 1, 12}, {i, 1, n}]]