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 A140322 #16 Sep 08 2022 08:45:34
%S A140322 1,2,11,42,171,682,2731,10922,43691,174762,699051,2796202,11184811,
%T A140322 44739242,178956971,715827882,2863311531,11453246122,45812984491,
%U A140322 183251937962,733007751851,2932031007402,11728124029611,46912496118442,187649984473771,750599937895082
%N A140322 a(n) = -1/6 + (-1)^n/2 + 2*4^n/3.
%C A140322 a(n+1) - 4a(n)= period 2: repeat -2, 3.
%H A140322 Vincenzo Librandi, <a href="/A140322/b140322.txt">Table of n, a(n) for n = 0..1000</a>
%H A140322 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (4,1,-4)
%F A140322 a(n) = 4*a(n-1) + a(n-2) - 4*a(n-3).
%F A140322 G.f.: ( 1 - 2*x + 2*x^2 ) / ( (x-1)*(4*x-1)*(1+x) ). - _R. J. Mathar_, Nov 21 2011
%t A140322 LinearRecurrence[{4,1,-4},{1,2,11},30] (* _Harvey P. Dale_, Sep 17 2013 *)
%o A140322 (Magma) [-1/6+(1/2)*(-1)^n+(2/3)*4^n: n in [0..25]]; // _Vincenzo Librandi_, Aug 09 2011
%K A140322 nonn,easy
%O A140322 0,2
%A A140322 _Paul Curtz_, May 26 2008