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A209789
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Half the number of (n+1) X 2 0..2 arrays with every 2 X 2 subblock having exactly one duplicate clockwise edge difference.
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1
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30, 204, 1380, 9348, 63300, 428676, 2902980, 19659012, 133130820, 901562244, 6105381060, 41345652228, 279992833860, 1896111996036, 12840473986500, 86955713884932, 588864257262660, 3987789852932484, 27005320351814340
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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) = 5*a(n-1) + 12*a(n-2).
G.f.: 6*x*(5 + 9*x) / (1 - 5*x - 12*x^2).
a(n) = (2^(-2-n)*(3*(5+sqrt(73))^n*(25+3*sqrt(73)) + (5-sqrt(73))^n*(-75+9*sqrt(73)))) / sqrt(73).
(End)
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EXAMPLE
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Some solutions for n=4:
..2..0....1..2....0..1....1..1....2..1....2..1....2..1....0..0....0..2....1..2
..1..0....0..2....2..1....2..0....1..1....0..0....0..0....2..1....2..2....0..2
..0..0....2..2....1..1....0..0....0..1....2..0....1..1....2..0....0..1....0..2
..1..0....2..0....2..0....2..2....2..2....0..0....1..0....1..0....0..1....2..2
..2..2....0..0....0..0....2..1....1..2....1..0....2..2....0..0....1..1....0..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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