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A011797
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a(n) = floor(C(n,6)/7).
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7
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0, 0, 0, 0, 0, 0, 0, 1, 4, 12, 30, 66, 132, 245, 429, 715, 1144, 1768, 2652, 3876, 5537, 7752, 10659, 14421, 19228, 25300, 32890, 42287, 53820, 67860, 84825, 105183, 129456, 158224, 192129, 231880, 278256
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OFFSET
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0,9
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COMMENTS
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a(n-1) is the number of aperiodic necklaces (Lyndon words) with 7 black beads and n-7 white beads.
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LINKS
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FORMULA
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G.f.: (1+x^3)^2/((1-x)^4(1-x^2)^2(1-x^7))*x^7.
a(n) = floor(binomial(n+1,7)/(n+1)). [Gary Detlefs, Nov 23 2011]
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MATHEMATICA
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CoefficientList[Series[x^6/7 (1/(1-x)^7-1/(1- x^7)), {x, 0, 40}], x]; (* Herbert Kociemba, Oct 16 2016 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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