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

0,2

Comments

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

Links

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

Example

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.

Sequence in context: A111023 A261751 A294679 * A345250 A008324 A333732

Adjacent sequences: A333157 A333158 A333159 * A333161 A333162 A333163

Keyword

nonn

Author

Andrew Howroyd, Mar 10 2020

Status

approved