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A251122
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Number of (n+1) X (2+1) 0..1 arrays with no 2 X 2 subblock having the sum of its diagonal elements greater than the maximum of its antidiagonal elements.
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1
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21, 40, 69, 117, 193, 315, 510, 823, 1326, 2136, 3442, 5550, 8955, 14458, 23355, 37743, 61015, 98661, 159564, 258097, 417516, 675450, 1092784, 1768032, 2860593, 4628380, 7488705, 12116793, 19605181, 31721631, 51326442, 83047675, 134373690
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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) = 4*a(n-1) - 5*a(n-2) + a(n-3) + 2*a(n-4) - a(n-5).
Empirical g.f.: x*(21 - 44*x + 14*x^2 + 20*x^3 - 12*x^4) / ((1 - x)^3*(1 - x - x^2)). - Colin Barker, Nov 25 2018
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EXAMPLE
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Some solutions for n=4:
..0..0..1....0..0..0....0..0..0....1..1..1....0..0..0....0..0..0....0..1..1
..0..0..1....1..1..1....0..0..0....0..0..0....1..1..1....1..1..1....0..0..0
..0..0..1....1..0..0....0..0..0....1..1..1....0..0..0....0..0..0....0..0..0
..1..0..1....1..0..0....0..0..0....0..0..0....0..0..0....0..0..0....1..1..1
..1..0..0....1..0..0....1..1..1....1..1..1....0..0..0....1..1..1....0..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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