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 A168269 #27 Sep 08 2022 08:45:48
%S A168269 3,3,7,7,11,11,15,15,19,19,23,23,27,27,31,31,35,35,39,39,43,43,47,47,
%T A168269 51,51,55,55,59,59,63,63,67,67,71,71,75,75,79,79,83,83,87,87,91,91,95,
%U A168269 95,99,99,103,103,107,107,111,111,115,115,119,119,123,123,127,127,131,131
%N A168269 a(n) = 2*n - (-1)^n.
%H A168269 Vincenzo Librandi, <a href="/A168269/b168269.txt">Table of n, a(n) for n = 1..1000</a>
%H A168269 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1).
%F A168269 G.f.: x*(3 + x^2)/( (1+x)*(x-1)^2 ). - _R. J. Mathar_, Jan 05 2011
%F A168269 a(n) = a(n-1) +a(n-2) -a(n-3). - _Vincenzo Librandi_, Sep 16 2013
%F A168269 E.g.f.: (-1 + exp(x) + 2*x*exp(2*x))*exp(-x). - _G. C. Greubel_, Jul 16 2016
%t A168269 CoefficientList[Series[(3 + x^2)/((1 + x) (x - 1)^2), {x, 0, 70}], x] (* _Vincenzo Librandi_, Sep 16 2013 *)
%t A168269 LinearRecurrence[{1,1,-1},{3,3,7},50] (* _G. C. Greubel_, Jul 16 2016 *)
%o A168269 (Magma) [2*n-(-1)^n: n in [1..70]]; // _Vincenzo Librandi_, Sep 16 2013
%o A168269 (PARI) a(n)=2*n-(-1)^n \\ _Charles R Greathouse IV_, Jul 16 2016
%Y A168269 Cf. A004767.
%K A168269 nonn,easy
%O A168269 1,1
%A A168269 _Vincenzo Librandi_, Nov 22 2009
%E A168269 New definition by _R. J. Mathar_, Jan 05 2011