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A168419 a(n) = 9*floor(n/2). 1

%I

%S 0,9,9,18,18,27,27,36,36,45,45,54,54,63,63,72,72,81,81,90,90,99,99,

%T 108,108,117,117,126,126,135,135,144,144,153,153,162,162,171,171,180,

%U 180,189,189,198,198,207,207,216,216,225,225,234,234,243,243,252,252,261

%N a(n) = 9*floor(n/2).

%H Vincenzo Librandi, <a href="/A168419/b168419.txt">Table of n, a(n) for n = 1..1000</a>

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

%F a(n) = 9*n - a(n-1) - 9, with n>1, a(1)=0.

%F a(n) = (9/4)*(-1 + (-1)^n + 2*n). - _Paolo P. Lava_, Nov 27 2009

%F G.f.: 9*x^2/((1+x)*(x-1)^2). - _Vincenzo Librandi_, Sep 19 2013

%F a(n) = a(n-1) +a(n-2) -a(n-3). - _Vincenzo Librandi_, Sep 19 2013

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

%t 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 *)

%t LinearRecurrence[{1,1,-1},{0,9,9},60] (* _Harvey P. Dale_, Apr 21 2019 *)

%o (MAGMA) [9*Floor(n/2): n in [1..70]]; // _Vincenzo Librandi_, Sep 19 2013

%Y Cf. A004526, A017377.

%K nonn,easy

%O 1,2

%A _Vincenzo Librandi_, Nov 25 2009

%E New definition by _Vincenzo Librandi_, Sep 19 2013

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Last modified August 13 05:41 EDT 2020. Contains 336442 sequences. (Running on oeis4.)