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A198710
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Number of n X 3 0..3 arrays with values 0..3 introduced in row major order and no element equal to any horizontal or vertical neighbor.
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3
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2, 25, 401, 6548, 107042, 1749965, 28609241, 467717288, 7646461682, 125007943505, 2043688517681, 33411178843628, 546221629207922, 8929887496964645, 145989990956749721, 2386712874803449568, 39019101990629849762
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OFFSET
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1,1
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 19*a(n-1) - 45*a(n-2) + 27*a(n-3).
Empirical g.f.: x*(2 - 13*x + 16*x^2) / ((1 - x)*(1 - 18*x + 27*x^2)). - Colin Barker, Mar 02 2018
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EXAMPLE
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Some solutions with all values from 0 to 3 for n=4:
..0..1..2....0..1..2....0..1..0....0..1..2....0..1..0....0..1..2....0..1..0
..2..0..3....2..3..1....1..0..1....3..2..3....2..0..2....2..3..0....1..2..3
..0..1..0....0..1..2....0..2..3....2..3..0....0..3..1....0..2..1....3..0..1
..3..2..3....3..2..1....3..0..1....1..2..3....2..1..3....1..0..3....0..3..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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