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A188237
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Number of nondecreasing arrangements of 4 numbers in -(n+2)..(n+2) with sum zero and not more than two numbers equal.
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1
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15, 30, 52, 81, 121, 172, 234, 311, 403, 510, 636, 781, 945, 1132, 1342, 1575, 1835, 2122, 2436, 2781, 3157, 3564, 4006, 4483, 4995, 5546, 6136, 6765, 7437, 8152, 8910, 9715, 10567, 11466, 12416, 13417, 14469, 15576, 16738, 17955, 19231, 20566, 21960
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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-1) - 3*a(n-2) + 2*a(n-3) - 3*a(n-4) + 3*a(n-5) - a(n-6).
Empirical g.f.: x*(15 - 15*x + 7*x^2 - 15*x^3 + 19*x^4 - 7*x^5) / ((1 - x)^4*(1 + x + x^2)). - Colin Barker, Apr 27 2018
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EXAMPLE
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Some solutions for n=4:
.-5...-4...-6...-3...-2...-5...-4...-4...-4...-4...-1...-6...-3...-2...-5...-4
.-3....1...-6...-1...-2....0...-1...-1....0...-4....0...-3...-2...-1...-1...-3
..2....1....6....1....0....0....1...-1....0....4....0....3....2....0....3....2
..6....2....6....3....4....5....4....6....4....4....1....6....3....3....3....5
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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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