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A202973
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Number of n X 2 0..1 arrays with every nonzero element less than or equal to at least two horizontal and vertical neighbors.
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5
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1, 2, 4, 7, 14, 31, 69, 155, 354, 814, 1875, 4326, 9993, 23095, 53387, 123430, 285394, 659913, 1525942, 3528541, 8159347, 18867623, 43629460, 100888804, 233295503, 539473228, 1247479743, 2884676711, 6670537293, 15424975984, 35668774074
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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) = 3*a(n-1) - 2*a(n-2) + 2*a(n-3) - 2*a(n-4) - a(n-5).
Empirical g.f.: x*(1 - x - 3*x^3 - x^4) / (1 - 3*x + 2*x^2 - 2*x^3 + 2*x^4 + x^5). - Colin Barker, Feb 19 2018
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EXAMPLE
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Some solutions for n=5:
..0..0....0..0....1..1....0..0....1..1....0..0....1..1....1..1....1..1....1..1
..0..0....1..1....1..1....1..1....1..1....0..0....1..1....1..1....1..1....1..1
..0..0....1..1....0..0....1..1....0..0....0..0....1..1....1..1....1..0....0..1
..1..1....0..0....1..1....1..1....0..0....0..0....0..0....1..1....1..1....1..1
..1..1....0..0....1..1....0..0....0..0....0..0....0..0....1..1....1..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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