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A233637
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Number of (n+1) X (1+1) 0..2 arrays with every 2 X 2 subblock having the sum of the squares of the edge differences equal to 2.
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1
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24, 90, 324, 1188, 4320, 15768, 57456, 209520, 763776, 2784672, 10152000, 37012032, 134936064, 491944320, 1793505024, 6538675968, 23838382080, 86908819968, 316847932416, 1155148784640, 4211385163776, 15353663035392, 55975637053440
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OFFSET
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1,1
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LINKS
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FORMULA
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Empirical: a(n) = 2*a(n-1) + 6*a(n-2).
G.f.: 6*x*(4 + 7*x) / (1 - 2*x - 6*x^2).
a(n) = ((1-sqrt(7))^n*(-17+7*sqrt(7)) + (1+sqrt(7))^n*(17+7*sqrt(7))) / (2*sqrt(7)).
(End)
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EXAMPLE
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Some solutions for n=5:
..1..1....1..2....0..1....0..0....1..1....1..0....0..1....1..0....2..2....0..1
..1..2....1..2....0..1....1..0....2..1....1..1....1..1....1..0....2..1....0..1
..1..2....1..2....1..1....1..0....2..1....0..1....0..0....1..1....1..1....0..1
..2..2....2..2....0..1....1..0....2..1....1..1....1..0....2..1....0..1....1..1
..1..1....1..1....1..1....1..0....1..1....0..1....1..1....1..1....1..1....1..0
..2..1....0..0....0..1....1..1....0..0....0..0....0..1....2..2....1..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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