A145948 Number of n X n binary arrays symmetric about the diagonal and under 90-degree rotation with all ones connected in a 3 X 2 elbow 1,1 1,2 1,3 2,3 in any orientation.

1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 13, 13, 41, 41, 227, 227, 1869, 1869, 21295, 21295, 308993, 308993, 6084845, 6084845, 167200773, 167200773, 6380227531, 6380227531, 331792369009, 331792369009

Offset

1,9

Links

Table of n, a(n) for n=1..30.

Example

Maximal 9 X 9 example:
  0 0 1 1 0 1 1 0 0
  0 0 0 1 0 1 0 0 0
  1 0 0 1 0 1 0 0 1
  1 1 1 0 0 0 1 1 1
  0 0 0 0 0 0 0 0 0
  1 1 1 0 0 0 1 1 1
  1 0 0 1 0 1 0 0 1
  0 0 0 1 0 1 0 0 0
  0 0 1 1 0 1 1 0 0

Crossrefs

Sequence in context: A146051 A146229 A146020 * A049768 A209390 A363630

Adjacent sequences: A145945 A145946 A145947 * A145949 A145950 A145951

Keyword

nonn

Author

R. H. Hardin, Oct 25 2008

Status

approved