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A168414
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a(n) = (18*n - 9*(-1)^n - 3)/4.
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1
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6, 6, 15, 15, 24, 24, 33, 33, 42, 42, 51, 51, 60, 60, 69, 69, 78, 78, 87, 87, 96, 96, 105, 105, 114, 114, 123, 123, 132, 132, 141, 141, 150, 150, 159, 159, 168, 168, 177, 177, 186, 186, 195, 195, 204, 204, 213, 213, 222, 222, 231, 231, 240, 240, 249, 249, 258
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OFFSET
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1,1
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (1,1,-1).
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FORMULA
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a(n) = 9*n - a(n-1) - 6, n>1.
a(n) = 3*A168236(n). - R. J. Mathar, Jul 10 2011
G.f. 3*x*(2 + x^2) / ( (1+x)*(x-1)^2 ). - R. J. Mathar, Jul 10 2011
a(n) = 6 + 9*Floor((n-1)/2). - Vincenzo Librandi, Sep 19 2013
From G. C. Greubel, Jul 22 2016: (Start)
a(n) = a(n-1) + a(n-2) - a(n-3).
E.g.f.: (3/4)*(-3 + 4*exp(x) +(6*x - 1)*exp(2*x))*exp(-x). (End)
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MATHEMATICA
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Table[6 + 9 Floor[(n - 1)/2], {n, 70}] (* or *) CoefficientList[Series[3 (2 + x^2)/((1 + x) (x - 1)^2), {x, 0, 70}], x] (* Vincenzo Librandi, Sep 19 2013 *)
LinearRecurrence[{1, 1, -1}, {6, 6, 15}, 60] (* Harvey P. Dale, May 17 2017 *)
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PROG
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(MAGMA) [6+9*Floor((n-1)/2): n in [1..70]]; // Vincenzo Librandi, Set 19 2013
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CROSSREFS
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Sequence in context: A072695 A085596 A107620 * A266223 A256675 A290931
Adjacent sequences: A168411 A168412 A168413 * A168415 A168416 A168417
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KEYWORD
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nonn,easy
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AUTHOR
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Vincenzo Librandi, Nov 25 2009
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EXTENSIONS
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Definition replaced by Lava formula of Nov 2009. - R. J. Mathar, Jul 10 2011
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STATUS
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approved
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