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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. 0
1, 1, 1, 1, 9, 17, 39, 147, 697, 3223, 21385, 138955, 1236361, 11421757, 147405903, 1921739323, 34678828327, 635167573009, 16140984723163, 417732159981711, 14999420093273161, 546619996126234299, 27635699247921456049 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 25 11:16 EDT 2021. Contains 348249 sequences. (Running on oeis4.)