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A199142
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Number of n X 1 0..3 arrays with values 0..3 introduced in row major order and each element equal to one or two horizontal and vertical neighbors.
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3
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0, 1, 1, 2, 3, 6, 11, 23, 47, 102, 221, 492, 1099, 2485, 5637, 12858, 29391, 67354, 154539, 355003, 816035, 1876862, 4318201, 9937840, 22874731, 52659593, 121237417, 279141170, 642732027, 1479959118, 3407837387, 7847200511
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OFFSET
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1,4
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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) + a(n-2) - 7*a(n-3) + a(n-4) + 3*a(n-5) for n>6.
Empirical g.f.: x^2*(1 - 2*x - 2*x^2 + 3*x^3 + x^4) / ((1 - x)*(1 - x - x^2)*(1 - x - 3*x^2)). - Colin Barker, Feb 22 2018
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EXAMPLE
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Some solutions for n=8:
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..1....0....0....1....1....1....0....1....1....0....1....0....0....0....1....0
..1....1....0....1....1....1....1....1....1....0....1....0....0....0....1....0
..2....1....1....1....1....0....1....2....1....0....2....1....0....1....1....0
..2....1....1....0....2....0....0....2....1....1....2....1....0....1....1....0
..2....0....0....0....2....1....0....1....0....1....3....1....0....2....2....1
..2....0....0....0....2....1....0....1....0....1....3....1....0....2....2....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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