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A168381
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a(n) = 4*n + 2*(-1)^n.
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3
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2, 10, 10, 18, 18, 26, 26, 34, 34, 42, 42, 50, 50, 58, 58, 66, 66, 74, 74, 82, 82, 90, 90, 98, 98, 106, 106, 114, 114, 122, 122, 130, 130, 138, 138, 146, 146, 154, 154, 162, 162, 170, 170, 178, 178, 186, 186, 194, 194, 202, 202, 210, 210, 218, 218, 226, 226, 234, 234
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = 8*n - a(n-1) - 4, with n>1, a(1)=2.
a(n) = 2 + 8*floor(n/2). (End)
E.g.f.: 2*(1 - exp(x) + 2*x*exp(2*x))*exp(-x). - G. C. Greubel, Jul 19 2016
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MATHEMATICA
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CoefficientList[Series[(2 + 8 x - 2 x^2)/((1 + x) (x -1)^2), {x, 0, 70}], x] (* Vincenzo Librandi, Sep 18 2013 *)
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy,less
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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