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 A168413 a(n) = 9*n - a(n-1) - 5, with a(1)=2. 1

%I

%S 2,11,11,20,20,29,29,38,38,47,47,56,56,65,65,74,74,83,83,92,92,101,

%T 101,110,110,119,119,128,128,137,137,146,146,155,155,164,164,173,173,

%U 182,182,191,191,200,200,209,209,218,218,227,227,236,236,245,245,254,254

%N a(n) = 9*n - a(n-1) - 5, with a(1)=2.

%H Vincenzo Librandi, <a href="/A168413/b168413.txt">Table of n, a(n) for n = 1..5000</a>

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1).

%F a(n) = (18*n + 9*(-1)^n - 1)/4, with n>=1. - _Paolo P. Lava_, Nov 27 2009

%F G.f.: x*(2 + 9*x - 2*x^2) / ( (1+x)*(x-1)^2 ). - _R. J. Mathar_, Jul 10 2011

%F E.g.f.: (1/4)*(9 - 8*exp(x) + (18*x - 1)*exp(2*x))*exp(-x). - _G. C. Greubel_, Jul 22 2016

%e 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.

%t LinearRecurrence[{1,1,-1}, {2, 11, 11}, 50] (* _G. C. Greubel_, Jul 22 2016 *)

%o (MAGMA) [-(1/4)+(9/4)*(-1)^n+(9/2)*n: n in [1..60]]

%Y Cf. A017186.

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Nov 25 2009

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Last modified May 16 19:46 EDT 2021. Contains 343951 sequences. (Running on oeis4.)