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A168569
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a(n) = 9*(3^n - 1)/2.
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2
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0, 9, 36, 117, 360, 1089, 3276, 9837, 29520, 88569, 265716, 797157, 2391480, 7174449, 21523356, 64570077, 193710240, 581130729, 1743392196, 5230176597, 15690529800, 47071589409, 141214768236, 423644304717, 1270932914160
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: 9*x / ( (3*x-1)*(x-1) ). (End)
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MATHEMATICA
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CoefficientList[Series[9 x / ((1 - x) (1 - 3 x)), {x, 0, 30}], x] (* Vincenzo Librandi, Sep 24 2014 *)
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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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