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A193642
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Number of arrays of -2..2 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, 5, 13, 37, 105, 297, 841, 2381, 6741, 19085, 54033, 152977, 433105, 1226197, 3471581, 9828661, 27826681, 78782265, 223046553, 631484317, 1787844005, 5061703197, 14330578721, 40572407841, 114867676321, 325210747045
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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Empirical: a(n) = 2*a(n-1) +2*a(n-2) +a(n-3).
Empirical: G.f.: -x*(1+3*x+x^2) / ( -1+2*x+2*x^2+x^3 ). - R. J. Mathar, Feb 19 2015
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EXAMPLE
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Some solutions for n=6
..1....0...-1....0...-1...-2...-2....1....1...-2...-1....2...-1....1....2....0
.-1....0....1...-1....1....2....2...-1...-1....2....1...-2....1...-1...-2....1
..2...-1...-1....1...-2...-2...-1....2....1...-2....2....1....0...-1....2...-1
.-2....1...-2....0....2....0....1...-2...-1....0...-2...-1....1....1...-2....2
.-1...-1....2....1....1....0...-1....0...-2....2....0...-2...-1...-1....2...-2
..1....1....0...-1...-1....0....1....0....2...-2....0....2....0....0...-2....2
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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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