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 A052904 #18 Jul 02 2025 16:01:58
%S A052904 1,1,6,12,44,112,352,976,2912,8320,24384,70400,205056,594176,1726976,
%T A052904 5010432,14552064,42237952,122642432,356028416,1033674752,3000893440,
%U A052904 8712372224,25293619200,73433153536,213191294976,618940727296
%N A052904 Expansion of (1-x)/(1-2x-4x^2+4x^3).
%H A052904 INRIA Algorithms Project, <a href="http://ecs.inria.fr/services/structure?nbr=882">Encyclopedia of Combinatorial Structures 882</a>
%H A052904 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (2,4,-4).
%F A052904 G.f.: -(-1+x)/(1-2*x-4*x^2+4*x^3)
%F A052904 Recurrence: {a(1)=1, a(0)=1, a(2)=6, 4*a(n)-4*a(n+1)-2*a(n+2)+a(n+3)=0}
%F A052904 Sum(-1/37*(-4-14*_alpha+13*_alpha^2)*_alpha^(-1-n), _alpha=RootOf(1-2*_Z-4*_Z^2+4*_Z^3))
%p A052904 spec := [S,{S=Sequence(Prod(Z,Union(Sequence(Z),Z,Z,Z,Z)))},unlabeled]: seq(combstruct[count](spec,size=n), n=0..20);
%t A052904 CoefficientList[Series[(1-x)/(1-2x-4x^2+4x^3),{x,0,30}],x] (* or *) LinearRecurrence[{2,4,-4},{1,1,6},30] (* _Harvey P. Dale_, Jan 17 2013 *)
%K A052904 easy,nonn
%O A052904 0,3
%A A052904 encyclopedia(AT)pommard.inria.fr, Jan 25 2000
%E A052904 More terms from _James Sellers_, Jun 08 2000