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A168072
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Expansion of (1-27x^2-108x^3)/((1-3x)^2*(1+3x+9x^2)).
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3
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1, 3, -18, -135, -405, -1944, -8019, -24057, -91854, -334611, -1003833, -3542940, -12223143, -36669429, -124357194, -416118303, -1248354909, -4132485216, -13559717115, -40679151345, -132497807238, -428874481323, -1286623443969, -4142299868388
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OFFSET
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0,2
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COMMENTS
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LINKS
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FORMULA
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a(n) = 3^n*(sin(2*Pi*n/3)/sqrt(3) - cos(2*Pi*n/3) - 2*n + 2). - Ilya Gutkovskiy, Jul 10 2016
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MATHEMATICA
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LinearRecurrence[{3, 0, 27, -81}, {1, 3, -18, -135}, 50] (* G. C. Greubel, Jul 09 2016 *)
CoefficientList[Series[(1 - 27 x^2 - 108 x^3) / ((1 - 3 x)^2 (1 + 3 x + 9 x^2)), {x, 0, 30}], x] (* Vincenzo Librandi, Jul 10 2016 *)
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PROG
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(PARI) Vec((1-27*x^2-108*x^3)/((1-3*x)^2*(1+3*x+9*x^2)) + O(x^30)) \\ Michel Marcus, Dec 03 2014
(Magma) I:=[1, 3, -18, -135]; [n le 4 select I[n] else 3*Self(n-1)+27*Self(n-3)-81*Self(n-4): n in [1..30]]; // Vincenzo Librandi, Jul 10 2016
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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