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A203290
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Number of arrays of 2n nondecreasing integers in -7..7 with sum zero and equal numbers greater than zero and less than zero
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1
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8, 80, 580, 3172, 13934, 51768, 168314, 491187, 1310474, 3241912, 7518232, 16487840, 34435060, 68887342, 132636714, 246789735, 445262312, 781274626, 1336560456, 2234216814, 3656356722, 5868037410, 9249277184, 14337411833
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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) -4*a(n-2) -2*a(n-3) +4*a(n-4) -2*a(n-5) +4*a(n-6) -4*a(n-7) +6*a(n-8) -6*a(n-9) -5*a(n-10) +4*a(n-11) +a(n-12) +2*a(n-13) +12*a(n-15) -17*a(n-16) +2*a(n-17) -2*a(n-18) +2*a(n-20) -2*a(n-21) +17*a(n-22) -12*a(n-23) -2*a(n-25) -a(n-26) -4*a(n-27) +5*a(n-28) +6*a(n-29) -6*a(n-30) +4*a(n-31) -4*a(n-32) +2*a(n-33) -4*a(n-34) +2*a(n-35) +4*a(n-36) -4*a(n-37) +a(n-38)
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EXAMPLE
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Some solutions for n=3
.-6...-5...-7...-7...-6...-7...-6...-7...-7...-6...-7...-7...-7...-7...-5...-7
.-4...-4...-7...-6...-1...-5...-6...-3...-6...-2...-6...-4...-2...-4...-5...-2
..0...-2...-1...-1...-1...-5...-3...-1...-3...-2...-2...-1...-1...-1...-3...-2
..0....1....5....4....1....5....3....3....3....2....4....1....3....3....4....3
..5....3....5....4....1....5....6....3....6....4....5....4....3....4....4....3
..5....7....5....6....6....7....6....5....7....4....6....7....4....5....5....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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