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A204032
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Number of (n+1) X 2 0..1 arrays with the sums of 2 X 2 subblocks nondecreasing rightwards and downwards.
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4
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16, 44, 121, 286, 676, 1482, 3249, 6840, 14400, 29640, 61009, 123994, 252004, 508526, 1026169, 2062468, 4145296, 8312988, 16670889, 33390774, 66879684, 133865682, 267944161, 536117488, 1072693504, 2145878288, 4292739361, 8586527026
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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) = 4*a(n-1) -18*a(n-3) +17*a(n-4) +22*a(n-5) -36*a(n-6) +20*a(n-8) -8*a(n-9).
Empirical g.f.: x*(16 - 20*x - 55*x^2 + 90*x^3 + 52*x^4 - 144*x^5 + 20*x^6 + 72*x^7 - 32*x^8) / ((1 - x)^3*(1 + x)*(1 - 2*x)*(1 - 2*x^2)^2). - Colin Barker, Feb 20 2018
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EXAMPLE
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Some solutions for n=4:
..1..0....1..1....1..1....0..1....1..1....0..0....0..0....1..0....1..1....0..0
..0..0....1..1....0..1....0..0....1..0....1..1....0..0....0..0....0..1....0..1
..0..1....1..1....1..1....1..0....1..1....0..1....1..1....0..1....1..1....1..0
..0..1....1..1....0..1....0..1....1..1....1..1....0..1....0..1....1..0....0..1
..0..1....1..1....1..1....1..1....1..1....1..1....1..1....0..1....1..1....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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