This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A168419 #27 Mar 04 2024 01:12:54
%S A168419 0,9,9,18,18,27,27,36,36,45,45,54,54,63,63,72,72,81,81,90,90,99,99,
%T A168419 108,108,117,117,126,126,135,135,144,144,153,153,162,162,171,171,180,
%U A168419 180,189,189,198,198,207,207,216,216,225,225,234,234,243,243,252,252,261
%N A168419 a(n) = 9*floor(n/2).
%H A168419 Vincenzo Librandi, <a href="/A168419/b168419.txt">Table of n, a(n) for n = 1..1000</a>
%H A168419 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1).
%F A168419 a(n) = 9*n - a(n-1) - 9, with n>1, a(1)=0.
%F A168419 G.f.: 9*x^2/((1+x)*(x-1)^2). - _Vincenzo Librandi_, Sep 19 2013
%F A168419 a(n) = a(n-1) +a(n-2) -a(n-3). - _Vincenzo Librandi_, Sep 19 2013
%F A168419 E.g.f.: (9/4)*(1 + (2*x - 1)*exp(2*x))*exp(-x). - _G. C. Greubel_, Jul 22 2016
%t A168419 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 A168419 LinearRecurrence[{1,1,-1},{0,9,9},60] (* _Harvey P. Dale_, Apr 21 2019 *)
%o A168419 (Magma) [9*Floor(n/2): n in [1..70]]; // _Vincenzo Librandi_, Sep 19 2013
%Y A168419 Cf. A004526, A017377.
%K A168419 nonn,easy
%O A168419 1,2
%A A168419 _Vincenzo Librandi_, Nov 25 2009
%E A168419 New definition by _Vincenzo Librandi_, Sep 19 2013