A333890 Number of non-isomorphic n X n nonnegative integer symmetric matrices with all row and column sums equal to 5 up to permutations of rows and columns.

1, 1, 3, 13, 74, 556, 5369, 64000, 917235, 15450781, 300882997, 6682784998, 167423745058, 4687321410460, 145487540598936, 4972006889998672, 185965612590706251, 7572297055379416985, 334097417273761302271, 15905277840810391655517, 813931037149014145154401

Offset: 0

Author

Andrew Howroyd, Apr 08 2020

Keywords

• nonn

Crossrefs

Column k=5 of A333737.

Formula

The a(2) = 3 matrices are:

[0 5] [1 4] [2 3]

[5 0] [4 1] [3 2]