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A168273
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a(n) = 2*n + (-1)^n - 1.
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8
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0, 4, 4, 8, 8, 12, 12, 16, 16, 20, 20, 24, 24, 28, 28, 32, 32, 36, 36, 40, 40, 44, 44, 48, 48, 52, 52, 56, 56, 60, 60, 64, 64, 68, 68, 72, 72, 76, 76, 80, 80, 84, 84, 88, 88, 92, 92, 96, 96, 100, 100, 104, 104, 108, 108, 112, 112, 116, 116, 120, 120, 124, 124, 128, 128, 132
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OFFSET
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1,2
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LINKS
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FORMULA
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G.f.: 4*x^2/( (1+x)*(1-x)^2).
E.g.f.: (1 + (2*x - 1)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 16 2016
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MATHEMATICA
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CoefficientList[Series[4 x / ((1+x) (1-x)^2), {x, 0, 70}], x] (* Vincenzo Librandi, May 14 2013 *)
LinearRecurrence[{1, 1, -1}, {0, 4, 4}, 50] (* G. C. Greubel, Jul 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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