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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
OFFSET
1,5
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
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 25 2008
STATUS
approved