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A198279
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Number of 2n X 4 0..2 arrays with values 0..2 introduced in row major order and each element equal to exactly two horizontal and vertical neighbors.
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1
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1, 4, 14, 52, 190, 700, 2574, 9476, 34878, 128396, 472654, 1739988, 6405438, 23580508, 86807566, 319567268, 1176432574, 4330837036, 15943242574, 58692346740, 216065933246, 795410139132, 2928167715854, 10779553536580
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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) = 4*a(n-1) +a(n-2) -8*a(n-3).
Empirical g.f.: x*(1 - 3*x^2) / (1 - 4*x - x^2 + 8*x^3). - Colin Barker, May 14 2018
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EXAMPLE
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Some solutions for n=3:
..0..0..1..1....0..0..1..1....0..0..0..0....0..0..1..1....0..0..1..1
..0..0..1..1....0..0..1..1....0..1..1..0....0..0..1..1....0..0..1..1
..1..1..2..2....2..2..2..2....0..1..1..0....2..2..0..0....2..2..2..2
..1..1..2..2....2..0..0..2....0..0..0..0....2..2..0..0....2..1..1..2
..0..0..1..1....2..0..0..2....2..2..1..1....0..0..2..2....2..1..1..2
..0..0..1..1....2..2..2..2....2..2..1..1....0..0..2..2....2..2..2..2
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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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