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

0,3

Links

Table of n, a(n) for n=0..20.

Formula

The a(2) = 3 matrices are:

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

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

Crossrefs

Column k=5 of A333737.

Sequence in context: A020094 A189886 A343787 * A009382 A110193 A038762

Adjacent sequences: A333887 A333888 A333889 * A333891 A333892 A333893

Keyword

nonn

Author

Andrew Howroyd, Apr 08 2020

Status

approved