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A209944
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Half the number of (n+1) X 2 0..2 arrays with every 2 X 2 subblock having at most one duplicate clockwise edge difference.
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1
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34, 258, 1956, 14832, 112464, 852768, 6466176, 49030272, 371775744, 2819017728, 21375415296, 162080704512, 1228989210624, 9318903717888, 70661292834816, 535794601623552, 4062703123759104, 30805753962037248, 233586961257332736
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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) = 6*a(n-1) + 12*a(n-2).
G.f.: 2*x*(17 + 27*x) / (1 - 6*x - 12*x^2).
a(n) = ((3-sqrt(21))^n*(-41+9*sqrt(21)) + (3+ sqrt(21))^n*(41+9*sqrt(21))) / (4*sqrt(21)).
(End)
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EXAMPLE
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Some solutions for n=4:
..2..0....0..1....1..1....2..1....2..1....2..1....2..1....2..2....1..2....2..0
..2..2....2..0....2..0....0..0....0..2....2..2....0..2....1..2....0..2....1..2
..0..1....1..2....0..1....1..1....1..1....1..2....1..2....2..2....0..2....0..2
..2..1....2..0....2..2....1..0....1..2....0..2....2..2....1..2....2..2....1..0
..2..1....0..1....2..1....2..2....1..1....2..2....1..0....1..1....0..2....2..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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