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A191344
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Number of n X n symmetric binary matrices with each 1 adjacent to exactly 2 horizontally, vertically or diagonally neighboring 1s
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0
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1, 1, 3, 11, 47, 294, 2274, 23217, 346865, 7054923, 194307949, 7369451741, 380583130482, 26850075718493, 2600396553939968, 344812336151621752, 62585126371789861439, 15557855832828751119291
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OFFSET
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1,3
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LINKS
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EXAMPLE
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Some solutions for n=4
..0..1..1..0....0..0..0..0....0..0..0..0....1..1..0..0....1..1..1..0
..1..1..0..1....0..0..1..1....0..1..1..0....1..0..1..0....1..0..0..1
..1..0..0..1....0..1..0..1....0..1..0..1....0..1..0..1....1..0..0..1
..0..1..1..1....0..1..1..0....0..0..1..1....0..0..1..1....0..1..1..1
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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