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A202982
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Number of n X 2 0..2 arrays with every nonzero element less than or equal to some NW, E or S neighbor.
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1
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1, 9, 63, 323, 1629, 8534, 44885, 234728, 1226239, 6410598, 33519355, 175245104, 916179060, 4789827101, 25041566175, 130918895222, 684451568104, 3578352893257, 18707840821315, 97805696796991, 511333945789384
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 9*a(n-1) -28*a(n-2) +60*a(n-3) -102*a(n-4) +84*a(n-5) -44*a(n-6) +25*a(n-7).
Empirical g.f.: x*(1 + 10*x^2 - 52*x^3 + 48*x^4 - 29*x^5 + 25*x^6) / (1 - 9*x + 28*x^2 - 60*x^3 + 102*x^4 - 84*x^5 + 44*x^6 - 25*x^7). - Colin Barker, Jun 03 2018
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EXAMPLE
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Some solutions for n=5:
..1..1....1..0....2..0....0..0....2..0....1..0....0..1....0..1....0..1....1..0
..1..1....1..1....2..0....0..2....2..2....2..1....2..1....2..2....2..1....1..2
..1..1....0..0....2..0....2..2....1..1....2..1....2..2....1..2....2..2....2..2
..2..0....1..1....2..2....2..2....2..1....2..0....1..1....1..1....2..1....0..2
..2..2....0..1....1..1....1..1....2..2....2..2....0..0....1..1....2..2....0..0
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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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