A352258 Number of symmetric binary n X n matrices with no 2 X 2 submatrix of all 1s.

2, 7, 42, 399, 5614, 112221, 3102020, 116076057, 5774524092, 376068483351, 31643635513816, 3401292647423655, 462391295351625128, 78801283167350942685, 1775935516860530625139, 230933325874558862792569

Offset

1,1

Comments

Equivalently, the number of labeled graphs (loops but not multiple edges allowed) with none of these subgraphs: 4-cycle, edge with a loop on each end, triangle with at least one loop.

Links

Table of n, a(n) for n=1..16.

Crossrefs

Row sums of A350189.

Cf. A345249 (traceless matrices).

Sequence in context: A066383 A011802 A007065 * A005130 A091669 A108042

Adjacent sequences: A352255 A352256 A352257 * A352259 A352260 A352261

Keyword

nonn,hard

Author

Brendan McKay, Mar 09 2022

Status

approved