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A198662
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Number of n X 1 0..4 arrays with values 0..4 introduced in row major order and each element equal to one or two horizontal and vertical neighbors.
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2
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0, 1, 1, 2, 3, 6, 11, 23, 47, 103, 226, 517, 1194, 2830, 6778, 16498, 40501, 100420, 250513, 628749, 1584525, 4007957, 10164528, 25835883, 65777232, 167694004, 427960360, 1093068944, 2793604179, 7143313914, 18272673575, 46755936515
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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) = 4*a(n-1) + a(n-2) - 17*a(n-3) + 6*a(n-4) + 21*a(n-5) - 6*a(n-6) - 8*a(n-7) for n>8.
Empirical g.f.: x^2*(1 - 3*x^2 - x^3)*(1 - 3*x + 3*x^3) / ((1 - x)*(1 + x)*(1 - 2*x)*(1 - x - x^2)*(1 - x - 4*x^2)). - Colin Barker, Mar 02 2018
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EXAMPLE
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All solutions for n=5:
..0....0....0
..0....0....0
..1....0....0
..1....0....1
..1....0....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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