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A193643
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Number of arrays of -3..3 integers x(1..n) with every x(i) in a subsequence of length 1 or 2 with sum zero
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1
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1, 7, 19, 67, 217, 721, 2377, 7855, 25939, 85675, 282961, 934561, 3086641, 10194487, 33670099, 111204787, 367284457, 1213058161, 4006458937, 13232434975, 43703763859, 144343726555, 476734943521, 1574548557121, 5200380614881
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OFFSET
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1,2
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COMMENTS
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Column 3 of A193648
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LINKS
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R. H. Hardin, Table of n, a(n) for n = 1..200
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FORMULA
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Empirical: a(n) = 2*a(n-1) +4*a(n-2) +a(n-3)
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EXAMPLE
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Some solutions for n=6
..2....1...-1....0....0....0....1....0....2...-2....2....1...-3....0....0....0
.-2...-1....1...-1...-3....0...-1....3...-2....2...-2...-1....3...-2....0....0
.-1....1....2....1....3....0....1...-3....2...-3...-2...-3....1....2....2....0
..1....0...-2...-3...-1...-2....1....3....0....3....2....3...-1....0...-2...-3
.-1...-3....0....3....1....2...-1...-3...-2....0....1...-2....2....2....2....3
..0....3....0...-3....0....0....1....0....2....0...-1....2...-2...-2...-2....0
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CROSSREFS
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Sequence in context: A155384 A155218 A046137 * A122484 A155242 A155333
Adjacent sequences: A193640 A193641 A193642 * A193644 A193645 A193646
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KEYWORD
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nonn
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AUTHOR
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R. H. Hardin Aug 02 2011
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STATUS
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approved
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