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A145940 Number of n X n binary arrays symmetric about the diagonal and 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, 3, 3, 7, 7, 23, 23, 131, 131, 971, 971, 9431, 9431, 139347, 139347, 2886057, 2886057, 82544813, 82544813, 3341873733, 3341873733, 191910369845, 191910369845, 15522222886741, 15522222886741, 1764362997792863 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

LINKS

Table of n, a(n) for n=1..29.

EXAMPLE

Maximal 8 X 8 example:

  1 1 0 0 0 0 1 1

  1 0 1 0 0 1 0 1

  0 1 1 0 0 1 1 0

  0 0 0 0 0 0 0 0

  0 0 0 0 0 0 0 0

  0 1 1 0 0 1 1 0

  1 0 1 0 0 1 0 1

  1 1 0 0 0 0 1 1

CROSSREFS

Sequence in context: A146599 A107222 A050613 * A147103 A003133 A021300

Adjacent sequences:  A145937 A145938 A145939 * A145941 A145942 A145943

KEYWORD

nonn

AUTHOR

R. H. Hardin, Oct 25 2008

STATUS

approved

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Last modified October 21 05:28 EDT 2021. Contains 348141 sequences. (Running on oeis4.)