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A168419
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a(n) = 9*floor(n/2).
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1
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0, 9, 9, 18, 18, 27, 27, 36, 36, 45, 45, 54, 54, 63, 63, 72, 72, 81, 81, 90, 90, 99, 99, 108, 108, 117, 117, 126, 126, 135, 135, 144, 144, 153, 153, 162, 162, 171, 171, 180, 180, 189, 189, 198, 198, 207, 207, 216, 216, 225, 225, 234, 234, 243, 243, 252, 252, 261
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OFFSET
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1,2
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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) - 9, with n>1, a(1)=0.
a(n) = (9/4)*(-1 + (-1)^n + 2*n). - Paolo P. Lava, Nov 27 2009
G.f.: 9*x^2/((1+x)*(x-1)^2). - Vincenzo Librandi, Sep 19 2013
a(n) = a(n-1) +a(n-2) -a(n-3). - Vincenzo Librandi, Sep 19 2013
E.g.f.: (9/4)*(1 + (2*x - 1)*exp(2*x))*exp(-x). - G. C. Greubel, Jul 22 2016
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MATHEMATICA
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Table[9 Floor[n/2], {n, 70}] (* or *) CoefficientList[Series[9 x/((1 + x) (x - 1)^2), {x, 0, 70}], x] (* Vincenzo Librandi, Sep 19 2013 *)
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PROG
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(MAGMA) [9*Floor(n/2): n in [1..70]]; // Vincenzo Librandi, Sep 19 2013
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CROSSREFS
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Cf. A004526, A017377.
Sequence in context: A040073 A003886 A065999 * A242892 A112440 A022092
Adjacent sequences: A168416 A168417 A168418 * A168420 A168421 A168422
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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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New definition by Vincenzo Librandi, Sep 19 2013
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STATUS
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approved
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