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A193645
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Number of arrays of -5..5 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, 11, 31, 151, 561, 2361, 9361, 38171, 153591, 621911, 2510721, 10150321, 41008321, 165729931, 669676751, 2706201271, 10935546481, 44190379881, 178571332881, 721601251291, 2915963545511, 11783308434231, 47615926483841
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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) +8*a(n-2) +a(n-3).
Empirical g.f.: x*(1 + 9*x + x^2) / (1 - 2*x - 8*x^2 - x^3). - Colin Barker, May 04 2018
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EXAMPLE
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Some solutions for n=6:
-5 -5 0 4 -5 5 4 0 -4 -5 0 0 0 2 1 1
5 5 3 -4 5 -5 -4 5 4 5 0 -2 2 -2 -1 -1
2 -1 -3 4 5 -3 1 -5 -4 -5 -2 2 -2 5 1 3
-2 1 -4 1 -5 3 -1 5 1 5 2 -2 0 -5 -3 -3
-3 5 4 -1 4 0 -1 -2 -1 -4 3 -3 0 1 3 -1
3 -5 0 1 -4 0 1 2 0 4 -3 3 0 -1 -3 1
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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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