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A204295
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Number of n X 2 0..3 arrays with every element neighboring horizontally or vertically both a 0 and a 1, and 2 introduced before 3 in row major order.
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1
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0, 4, 4, 16, 68, 212, 776, 3076, 11540, 44944, 177748, 700292, 2779272, 11069140, 44107780, 176038288, 703199588, 2809956020, 11232774920, 44913243940, 179603461748, 718287355024, 2872823053300, 11490415637348, 45959392743048
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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) = 4*a(n-1) +2*a(n-2) +4*a(n-3) -42*a(n-4) -30*a(n-5) +13*a(n-6) +38*a(n-7) +28*a(n-8) -16*a(n-9).
Empirical g.f.: 4*x^2*(1 - 3*x - 2*x^2 - 5*x^3 + 15*x^4 + 4*x^5 + 4*x^6 - 8*x^7) / ((1 - x)*(1 + x)*(1 - 4*x)*(1 - 3*x + x^2)*(1 + x + x^2)*(1 + 2*x + 4*x^2)). - Colin Barker, Jun 07 2018
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EXAMPLE
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Some solutions for n=5:
..0..0....0..1....0..1....1..1....0..0....1..0....0..1....0..1....1..0....0..0
..1..1....0..1....0..1....0..0....1..1....1..0....0..1....0..1....1..0....1..1
..0..0....2..1....1..1....2..1....0..1....0..1....2..0....0..1....1..0....0..2
..1..1....1..0....0..0....1..1....0..0....0..1....1..0....1..0....1..0....0..1
..0..0....1..0....1..1....0..0....1..1....0..1....1..0....1..0....1..0....0..1
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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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