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A225314
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Number of 7Xn -1,1 arrays such that the sum over i=1..7,j=1..n of i*x(i,j) is zero and rows are nondecreasing (ways to put n thrusters pointing east or west at each of 7 positions 1..n distance from the hinge of a south-pointing gate without turning the gate)
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1
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8, 87, 474, 1787, 5304, 13333, 29638, 60007, 112790, 199669, 336342, 543465, 847456, 1281681, 1887330, 2714817, 3824812, 5289809, 7195252, 9641399, 12744472, 16638757, 21477906, 27437211, 34714980, 43535143, 54148610, 66836145, 81909858
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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) = 3*a(n-2) +2*a(n-3) -3*a(n-4) -5*a(n-5) +4*a(n-7) +a(n-8) -2*a(n-9) +a(n-10) +3*a(n-11) -3*a(n-13) -a(n-14) +2*a(n-15) -a(n-16) -4*a(n-17) +5*a(n-19) +3*a(n-20) -2*a(n-21) -3*a(n-22) +a(n-24)
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EXAMPLE
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Some solutions for n=4
..1..1..1..1...-1..1..1..1...-1.-1..1..1...-1.-1.-1.-1...-1.-1.-1.-1
.-1.-1.-1..1...-1.-1.-1..1...-1.-1.-1.-1....1..1..1..1...-1.-1.-1.-1
.-1.-1.-1..1...-1.-1..1..1...-1.-1.-1..1...-1.-1.-1..1...-1.-1.-1.-1
..1..1..1..1...-1.-1.-1..1....1..1..1..1...-1.-1..1..1...-1..1..1..1
.-1.-1.-1.-1...-1..1..1..1...-1.-1..1..1...-1.-1.-1..1....1..1..1..1
..1..1..1..1...-1.-1..1..1...-1..1..1..1...-1..1..1..1....1..1..1..1
.-1.-1.-1..1...-1.-1..1..1...-1.-1.-1..1...-1.-1..1..1...-1.-1.-1.-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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