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 A133405 #23 Feb 03 2025 18:54:02
%S A133405 0,0,0,1,3,9,26,78,234,703,2109,6327,18980,56940,170820,512461,
%T A133405 1537383,4612149,13836446,41509338,124528014,373584043,1120752129,
%U A133405 3362256387,10086769160,30260307480,90780922440,272342767321,817028301963,2451084905889,7353254717666
%N A133405 a(n) = 3*a(n-1) - a(n-3) + 3*a(n-4), with initial values 0,0,0,1.
%H A133405 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3,0,-1,3).
%F A133405 O.g.f.: -x^3/((3*x-1)*(x+1)*(x^2-x+1)) = -(1/28)/(3*x-1)-(1/12)/(x+1)+(1/21)*(-5*x+1)/(x^2-x+1). - _R. J. Mathar_, Nov 28 2007
%t A133405 LinearRecurrence[{3, 0, -1, 3}, {0, 0, 0, 1}, 60] (* _Vladimir Joseph Stephan Orlovsky_, Jun 20 2011 *)
%K A133405 nonn
%O A133405 0,5
%A A133405 _Paul Curtz_, Nov 24 2007