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A202964
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Number of arrays of 4 integers in -n..n with sum zero and adjacent elements differing in absolute value.
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1
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4, 28, 108, 268, 544, 972, 1576, 2392, 3456, 4792, 6436, 8424, 10780, 13540, 16740, 20404, 24568, 29268, 34528, 40384, 46872, 54016, 61852, 70416, 79732, 89836, 100764, 112540, 125200, 138780, 153304, 168808, 185328, 202888, 221524, 241272
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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.: 4*x*(1 + 4*x + 9*x^2 + 5*x^3 + 5*x^4) / ((1 - x)^4*(1 + x + x^2)). - Colin Barker, Jun 03 2018
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EXAMPLE
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Some solutions for n=5:
.-4....1...-1....0...-1....0....0....0....3...-2...-2...-5....0...-4....1...-5
..5...-4....2...-4....0...-3...-1...-2...-4...-1....5....4....3....1...-2....1
..2....1...-5....3....3....2....3....4...-2....5...-2....0....2....4....4....4
.-3....2....4....1...-2....1...-2...-2....3...-2...-1....1...-5...-1...-3....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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