A333890 - OEIS

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

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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