A333738 Number of non-isomorphic n X n nonnegative integer symmetric matrices with all row and column sums equal to n up to permutations of rows and columns.

1, 1, 2, 5, 33, 556, 31781, 5882230, 3589936407, 7347418294141, 51304793433150418, 1240428029662246026001, 105148289475978338858008298, 31582581551955332317665959184087

Offset

0,3

Links

Table of n, a(n) for n=0..13.

Example

The a(3) = 5 matrices are:
  [0, 0, 3]  [0, 1, 2]  [0, 1, 2]  [1, 0, 2]  [1, 1, 1]
  [0, 3, 0]  [1, 1, 1]  [1, 2, 0]  [0, 3, 0]  [1, 1, 1]
  [3, 0, 0]  [2, 1, 0]  [2, 0, 1]  [2, 0, 1]  [1, 1, 1]

Crossrefs

Main diagonal of A333737.

Sequence in context: A366327 A197974 A208985 * A114793 A254429 A298945

Adjacent sequences: A333735 A333736 A333737 * A333739 A333740 A333741

Keyword

nonn,more

Author

Andrew Howroyd, Apr 08 2020

Status

approved