A204030 Symmetric matrix based on f(i,j) = gcd(i+1, j+1), by antidiagonals.

2, 1, 1, 2, 3, 2, 1, 1, 1, 1, 2, 1, 4, 1, 2, 1, 3, 1, 1, 3, 1, 2, 1, 2, 5, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 2, 3, 4, 1, 6, 1, 4, 3, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 7, 2, 1, 2, 1, 2, 1, 3, 1, 5, 3, 1, 1, 3, 5, 1, 3, 1, 2, 1, 4, 1, 2, 1, 8, 1, 2, 1, 4, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1

Offset

1,1

Comments

A204030 represents the matrix M given by f(i,j) = gcd(i+1, j+1) for i >= 1 and j >= 1. See A204031 for characteristic polynomials of principal submatrices of M, with interlacing zeros. See A204016 for a guide to other choices of M.

Links

Table of n, a(n) for n=1..99.

Example

Northwest corner:
  2 1 2 1 2 1 2 1
  1 3 1 1 3 1 1 3
  2 1 4 1 2 1 4 1
  1 1 1 5 1 1 1 1
  2 3 2 1 6 1 2 3
  1 1 1 1 1 7 1 1

Mathematica

f[i_, j_] := GCD[i + 1, j + 1];
m[n_] := Table[f[i, j], {i, 1, n}, {j, 1, n}]
TableForm[m[8]] (* 8 X 8 principal submatrix *)
Flatten[Table[f[i, n + 1 - i],
  {n, 1, 15}, {i, 1, n}]]  (* A204030 *)
p[n_] := CharacteristicPolynomial[m[n], x];
c[n_] := CoefficientList[p[n], x]
TableForm[Flatten[Table[p[n], {n, 1, 10}]]]
Table[c[n], {n, 1, 12}]
Flatten[%]                 (* A204111 *)
TableForm[Table[c[n], {n, 1, 10}]]

Crossrefs

Cf. A204111, A204016, A202453.

Sequence in context: A072782 A337014 A122563 * A234503 A333267 A236325

Adjacent sequences: A204027 A204028 A204029 * A204031 A204032 A204033

Keyword

nonn,tabl

Author

Clark Kimberling, Jan 11 2012

Status

approved