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A251328
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Number of (n+1) X (1+1) 0..2 arrays with every 2 X 2 subblock summing to 2 4 or 6.
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1
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39, 171, 753, 3333, 14823, 66219, 297057, 1337733, 6045495, 27408747, 124625745, 568146309, 2596130823, 11887635627, 54533628609, 250576195845, 1153020767319, 5312272049259, 24501992068785, 113120150702085, 522688044131367
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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) = 8*a(n-1) - 13*a(n-2) - 12*a(n-3).
G.f.: 3*x*(13 - 47*x - 36*x^2) / ((1 - 4*x)*(1 - 4*x - 3*x^2)).
a(n) = (7*2^(3+2*n) + (35-13*sqrt(7))*(2-sqrt(7))^n + (2+sqrt(7))^n*(35+13*sqrt(7))) / 14.
(End)
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EXAMPLE
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Some solutions for n=4:
..2..0....2..0....2..1....0..1....1..2....1..1....2..0....2..2....2..0....0..0
..1..1....0..2....2..1....2..1....0..1....1..1....1..1....0..2....1..1....2..0
..1..1....0..0....1..0....0..1....1..0....1..1....0..2....2..0....1..1....2..2
..0..0....1..1....1..2....1..2....2..1....0..2....0..2....0..2....0..0....1..1
..2..2....0..2....1..2....1..2....1..2....0..2....2..2....2..0....1..1....0..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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