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A145794
Number of n X n binary arrays symmetric about the diagonal and under 90-degree rotation with all ones connected only either four adjacent vertically or four adjacent horizontally.
0
1, 1, 1, 1, 1, 2, 1, 3, 2, 5, 6, 12, 20, 34, 68, 154, 265, 709, 1281, 3847, 8603, 25073, 71217, 206107, 695670, 2185029, 7989257, 27851353, 111404338, 424685942
OFFSET
1,6
CROSSREFS
Sequence in context: A102517 A062951 A263150 * A176741 A266138 A014000
KEYWORD
nonn
AUTHOR
R. H. Hardin, Oct 19 2008
STATUS
approved