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A198717
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Number of n X 2 0..6 arrays with values 0..6 introduced in row major order and no element equal to any horizontal or vertical neighbor.
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3
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1, 4, 34, 499, 10507, 272410, 7817980, 234638905, 7176366133, 221220625936, 6841771033846, 211886983790431, 6565800345745279, 203504808219690982, 6308194354577750032, 195548116214389189477, 6061914804816147034345
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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) = 55*a(n-1) - 918*a(n-2) + 5818*a(n-3) - 13417*a(n-4) + 8463*a(n-5).
G.f.: x*(1 - 51*x + 732*x^2 - 3517*x^3 + 4419*x^4) / ((1 - x)*(1 - 3*x)*(1 - 7*x)*(1 - 13*x)*(1 - 31*x)).
a(n) = 11/30 + 3^n/8 + 7^(n-1)/6 + 13^(n-1)/12 + 31^(n-1)/120.
(End)
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EXAMPLE
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Some solutions with all values 0 to 6 for n=4:
..0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1....0..1
..2..3....2..3....2..3....2..3....2..3....2..3....2..0....2..3....2..3....2..3
..4..5....4..5....4..5....4..5....4..1....4..5....3..4....4..5....4..0....1..4
..6..1....6..0....2..6....6..2....5..6....6..4....5..6....0..6....5..6....5..6
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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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