A203955 Symmetric matrix based on (1,2,3,1,2,3,1,2,3...), by antidiagonals.

1, 2, 2, 3, 5, 3, 1, 8, 8, 1, 2, 5, 14, 5, 2, 3, 5, 11, 11, 5, 3, 1, 8, 11, 15, 11, 8, 1, 2, 5, 14, 13, 13, 14, 5, 2, 3, 5, 11, 14, 19, 14, 11, 5, 3, 1, 8, 11, 15, 19, 19, 15, 11, 8, 1, 2, 5, 14, 13, 16, 28, 16, 13, 14, 5, 2, 3, 5, 11, 14, 19, 22, 22, 19, 14, 11, 5, 3, 1, 8

Offset

1,2

Comments

Let s be the periodic sequence (1,2,3,1,2,3,...) 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 A203955 represents the matrix product M=T'*T. M is the self-fusion matrix of s, as defined at A193722. See A203956 for characteristic polynomials of principal submatrices of M, with interlacing zeros.

Links

Table of n, a(n) for n=1..80.

Example

Northwest corner:
1....2....3....1....2....3
2....5....8....5....5....8
3....8....14...11...11...14
1....5....11...15...13...14

Mathematica

t = {1, 2, 3}; t1 = Flatten[{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]  (* A203955 *)
m[i_, j_] := M[[i]][[j]];
Flatten[Table[m[i, n + 1 - i], {n, 1, 12}, {i, 1, n}]]

Crossrefs

Cf. A203956, A202453.

Sequence in context: A368255 A368256 A185688 * A039638 A090926 A023503

Adjacent sequences: A203952 A203953 A203954 * A203956 A203957 A203958

Keyword

nonn,tabl

Author

Clark Kimberling, Jan 08 2012

Status

approved