A145941 Number of n X n binary arrays symmetric under 90-degree rotation with all ones connected only in a 2 X 2 elbow 1,1 1,2 2,1 in any orientation.

1, 1, 1, 1, 9, 17, 39, 147, 697, 3223, 21385, 138955, 1236361, 11421757, 147405903, 1921739323, 34678828327, 635167573009, 16140984723163, 417732159981711, 14999420093273161, 546619996126234299, 27635699247921456049

Offset

1,5

Links

Table of n, a(n) for n=1..23.

Example

Maximal 8 X 8 example:
  1 1 0 1 1 0 1 1
  1 0 1 0 1 0 0 1
  0 0 1 1 0 1 1 0
  1 1 0 0 0 1 0 1
  1 0 1 0 0 0 1 1
  0 1 1 0 1 1 0 0
  1 0 0 1 0 1 0 1
  1 1 0 1 1 0 1 1

Crossrefs

Sequence in context: A147026 A055393 A147082 * A245542 A186298 A147245

Adjacent sequences: A145938 A145939 A145940 * A145942 A145943 A145944

Keyword

nonn

Author

R. H. Hardin, Oct 25 2008

Status

approved