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A146051
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Number of n X n binary arrays symmetric about the diagonal and under 90 degree rotation with all ones connected only in a 2X2 block with tail 1,1 1,2 1,3 2,2 2,3 in any orientation.
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0
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1, 1, 1, 1, 1, 1, 1, 1, 3, 3, 13, 13, 35, 35, 181, 181, 1303, 1303, 13131, 13131, 161693, 161693, 2592581, 2592581, 57377381, 57377381, 1720164275, 1720164275
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,9
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EXAMPLE
| Maximal 9 X 9 example
.0.0.1.1.0.1.1.0.0
.0.0.1.1.0.1.1.0.0
.1.1.0.1.0.1.0.1.1
.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
.1.1.0.1.0.1.0.1.1
.0.0.1.1.0.1.1.0.0
.0.0.1.1.0.1.1.0.0
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CROSSREFS
| Sequence in context: A146193 A146727 A146426 * A146229 A146020 A145948
Adjacent sequences: A146048 A146049 A146050 * A146052 A146053 A146054
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KEYWORD
| nonn
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AUTHOR
| R. H. Hardin (rhhardin(AT)att.net), Oct 26 2008
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