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 A168280 #23 Sep 08 2022 08:45:48
%S A168280 4,4,9,9,14,14,19,19,24,24,29,29,34,34,39,39,44,44,49,49,54,54,59,59,
%T A168280 64,64,69,69,74,74,79,79,84,84,89,89,94,94,99,99,104,104,109,109,114,
%U A168280 114,119,119,124,124,129,129,134,134,139,139,144,144,149,149,154,154,159
%N A168280 (1 - 5*(-1)^n + 10*n)/4.
%H A168280 Vincenzo Librandi, <a href="/A168280/b168280.txt">Table of n, a(n) for n = 1..1000</a>
%H A168280 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1).
%F A168280 a(n) = 5*n - a(n-1) - 2, with n>1, a(1)=4.
%F A168280 From _Colin Barker_, Jun 30 2012: (Start)
%F A168280 a(n) = a(n-1) +a(n-2) -a(n-3).
%F A168280 G.f.: x*(4 + x^2)/((1-x)^2*(1+x)). (End)
%F A168280 E.g.f.: (1/4)*(-5 + 4*exp(x) + (1 + 10*x)*exp(2*x))*exp(-x). - _G. C. Greubel_, Jul 16 2016
%t A168280 CoefficientList[Series[(4 + x^2) / ((1 - x)^2 (1 + x)), {x, 0, 80}], x] (* _Vincenzo Librandi_, Sep 16 2013 *)
%t A168280 LinearRecurrence[{1,1,-1},{4,4,9},80] (* _Harvey P. Dale_, Jul 29 2022 *)
%o A168280 (Magma) [(1-5*(-1)^n+10*n)/4: n in [1..70]]; // _Vincenzo Librandi_, Sep 16 2013
%K A168280 nonn,easy
%O A168280 1,1
%A A168280 _Vincenzo Librandi_, Nov 22 2009
%E A168280 New name from _Colin Barker_, Jun 30 2012