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A188212
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Number of nondecreasing arrangements of 4 numbers in -(n+2)..(n+2) with sum zero.
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1
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18, 33, 55, 86, 126, 177, 241, 318, 410, 519, 645, 790, 956, 1143, 1353, 1588, 1848, 2135, 2451, 2796, 3172, 3581, 4023, 4500, 5014, 5565, 6155, 6786, 7458, 8173, 8933, 9738, 10590, 11491, 12441, 13442, 14496, 15603, 16765, 17984, 19260, 20595, 21991
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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*(18 - 21*x + 10*x^2 - 16*x^3 + 21*x^4 - 8*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=3:
.-4...-5...-4...-5...-3...-1...-2...-2....0...-4...-3...-4...-2...-5...-4...-4
..1...-1...-1....1...-2...-1...-2...-1....0...-1...-3...-3...-2...-3...-4...-2
..1....2....1....2....0...-1....2....1....0....0....1....3....1....4....4....2
..2....4....4....2....5....3....2....2....0....5....5....4....3....4....4....4
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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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