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 A209008 Number of 4-bead necklaces labeled with numbers -n..n not allowing reversal, with sum zero and first and second differences in -n..n. 1
 1, 3, 5, 10, 16, 26, 38, 55, 75, 101, 131, 168, 210, 260, 316, 381, 453, 535, 625, 726, 836, 958, 1090, 1235, 1391, 1561, 1743, 1940, 2150, 2376, 2616, 2873, 3145, 3435, 3741, 4066, 4408, 4770, 5150, 5551, 5971, 6413, 6875, 7360, 7866, 8396, 8948, 9525, 10125 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Row 4 of A209007. LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 3*a(n-1) - 2*a(n-2) - 2*a(n-3) + 3*a(n-4) - a(n-5). Conjectures from Colin Barker, Jul 07 2018: (Start) G.f.: x*(1 - 2*x^2 + 3*x^3 - x^4) / ((1 - x)^4*(1 + x)). a(n) = (4*n^3 + 6*n^2 + 20*n + 48) / 48 for n even. a(n) = (4*n^3 + 6*n^2 + 20*n + 18) / 48 for n odd. (End) EXAMPLE Some solutions for n=6:   -2  0 -3 -3 -1 -3 -2 -3 -2 -3 -1 -2 -1 -2 -1 -2   -2  0  0 -2  1 -3  1 -1 -1  1 -1  1  0  0  0  2    2  0  3  3 -1  3  0  3  2  3  1  1 -1  0  0  0    2  0  0  2  1  3  1  1  1 -1  1  0  2  2  1  0 CROSSREFS Cf. A209007. Sequence in context: A287563 A184800 A267151 * A032279 A070558 A233758 Adjacent sequences:  A209005 A209006 A209007 * A209009 A209010 A209011 KEYWORD nonn AUTHOR R. H. Hardin, Mar 04 2012 STATUS approved

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Last modified October 15 05:43 EDT 2019. Contains 328026 sequences. (Running on oeis4.)