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 A168273 a(n) = 2*n + (-1)^n - 1. 8
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 Index entries for linear recurrences with constant coefficients, signature (1,1,-1). FORMULA From  R. J. Mathar, Jan 05 2011: (Start) G.f.: 4*x^2/( (1+x)*(1-x)^2). a(n) = 2*A052928(n). a(n) = A008586(floor(n/2)). (End) a(n) = 2*n - 2*(n mod 2). - Wesley Ivan Hurt, Jun 30 2013 E.g.f.: (1 + (2*x - 1)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 16 2016 MATHEMATICA 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 *) PROG (MAGMA) [2*n-1 + (-1)^n: n in [1..70]] // Vincenzo Librandi, May 14 2013 (PARI) a(n)=2*n-1+(-1)^n \\ Charles R Greathouse IV, Oct 07 2015 CROSSREFS Cf. A052928, A008586. Sequence in context: A053249 A071339 A146890 * A278933 A328527 A145447 Adjacent sequences:  A168270 A168271 A168272 * A168274 A168275 A168276 KEYWORD nonn,easy AUTHOR Vincenzo Librandi, Nov 22 2009 STATUS approved

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Last modified November 30 04:01 EST 2020. Contains 338781 sequences. (Running on oeis4.)