A333160 Number of non-isomorphic n X n symmetric binary matrices with an equal number of ones in every row and column up to permutation of rows and columns.

1, 2, 3, 4, 6, 8, 17, 36, 146, 1066, 15419, 406684, 19284912, 1635874946, 249424764407, 68725494158824, 34418706513939926, 31487353344361957012, 52887877379630894268187, 163777247316556715401451972, 939121048579630147375554814224

Offset: 0

Author

Andrew Howroyd, Mar 10 2020

Keywords

• nonn

Comments

a(n) is the number of regular bicolored graphs on 2n unlabeled nodes which are invariant when the two color classes are interchanged.

Examples

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

Crossrefs

Row sums of A333159.

Cf. A122082, A322698, A333162.