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A231280
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Number of n X 3 0..3 arrays x(i,j) with each element horizontally or antidiagonally next to at least one element with value (x(i,j)+1) mod 4, and upper left element zero.
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1
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0, 2, 8, 66, 400, 2722, 17688, 117026, 768800, 5064642, 33328168, 219411586, 1444225200, 9506897762, 62579419448, 411934939746, 2711589889600, 17849253534082, 117494042259528, 773413479117506, 5091052634882000
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OFFSET
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1,2
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LINKS
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FORMULA
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Empirical: a(n) = 4*a(n-1) + 17*a(n-2).
G.f.: 2*x^2 / (1 - 4*x - 17*x^2).
a(n) = ((2-sqrt(21))^n*(2+sqrt(21)) + (-2+sqrt(21))*(2+sqrt(21))^n)/(17*sqrt(21)).
(End)
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EXAMPLE
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Some solutions for n=3:
..0..1..0....0..1..2....0..1..0....0..1..2....0..1..2....0..1..2....0..1..0
..2..3..2....0..3..0....2..3..0....2..3..0....0..3..2....2..3..2....2..3..2
..0..1..0....2..1..0....2..1..0....2..1..0....2..1..0....0..1..0....2..1..0
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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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