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A168413
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a(n) = 9*n - a(n-1) - 5, with a(1)=2.
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1
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2, 11, 11, 20, 20, 29, 29, 38, 38, 47, 47, 56, 56, 65, 65, 74, 74, 83, 83, 92, 92, 101, 101, 110, 110, 119, 119, 128, 128, 137, 137, 146, 146, 155, 155, 164, 164, 173, 173, 182, 182, 191, 191, 200, 200, 209, 209, 218, 218, 227, 227, 236, 236, 245, 245, 254, 254
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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..5000
Index entries for linear recurrences with constant coefficients, signature (1,1,-1).
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FORMULA
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a(n) = (18*n + 9*(-1)^n - 1)/4, with n>=1. - Paolo P. Lava, Nov 27 2009
G.f.: x*(2 + 9*x - 2*x^2) / ( (1+x)*(x-1)^2 ). - R. J. Mathar, Jul 10 2011
E.g.f.: (1/4)*(9 - 8*exp(x) + (18*x - 1)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 22 2016
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EXAMPLE
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For n=2, a(2)=9*2-2-5=11; n=3, a(3)=9*3-11-5=11; n=4, a(4)=9*4-11-5=20.
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MATHEMATICA
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LinearRecurrence[{1, 1, -1}, {2, 11, 11}, 50] (* G. C. Greubel, Jul 22 2016 *)
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PROG
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(MAGMA) [-(1/4)+(9/4)*(-1)^n+(9/2)*n: n in [1..60]]
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CROSSREFS
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Cf. A017186.
Sequence in context: A027828 A106371 A145523 * A265561 A265545 A153705
Adjacent sequences: A168410 A168411 A168412 * A168414 A168415 A168416
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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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STATUS
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approved
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