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 A189318 #24 Jun 02 2025 04:01:57
%S A189318 5,5,25,65,225,705,2305,7425,24065,77825,251905,815105,2637825,
%T A189318 8536065,27623425,89391105,289275905,936116225,3029336065,9803137025,
%U A189318 31723618305,102659784705,332214042625,1075067224065,3478990618625,11258250133505
%N A189318 Expansion of 5*(1-2*x)/(1-3*x-2*x^2+4*x^3).
%C A189318 (Start) Let A be the unit-primitive matrix (see [Jeffery])
%C A189318 A=A_(10,4)=
%C A189318 (0 0 0 0 1)
%C A189318 (0 0 0 2 0)
%C A189318 (0 0 2 0 1)
%C A189318 (0 2 0 2 0)
%C A189318 (2 0 2 0 1).
%C A189318 Then a(n)=Trace(A^n). (End)
%C A189318 Evidently one of a class of accelerator sequences for Catalan's constant based on traces of successive powers of a unit-primitive matrix A_(N,r) (0<r<floor(N/2)) and for which the closed-form expression for a(n) is derived from the eigenvalues of A_(N,r).
%H A189318 L. E. Jeffery, <a href="/wiki/User:L._Edson_Jeffery/Unit-Primitive_Matrices">Unit-primitive matrices</a>.
%H A189318 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3, 2, -4).
%F A189318 G.f.: 5*(1-2*x)/(1-3*x-2*x^2+4*x^3).
%F A189318 a(n)=3*a(n-1)+2*a(n-2)-4*a(n-3), n>3, a(0)=5, a(1)=5, a(2)=25, a(3)=65.
%F A189318 a(n)=Sum_{k=1..5} ((w_k)^4-3*(w_k)^2+1)^n, w_k=2*cos((2*k-1)*Pi/10).
%F A189318 a(n)=1+2*(1-Sqrt(5))^n+2*(1+Sqrt(5))^n.
%F A189318 a(n)=5*A052899(n).
%t A189318 CoefficientList[Series[5(1-2x)/(1-3x-2x^2+4x^3),{x,0,30}],x] (* or *) LinearRecurrence[{3,2,-4},{5,5,25},30] (* _Harvey P. Dale_, Jun 02 2014 *)
%o A189318 (PARI) Vec(5*(1-2*x)/(1-3*x-2*x^2+4*x^3)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 25 2012
%Y A189318 Cf. A052899.
%Y A189318 A189315, A189316, A189317.
%K A189318 nonn,easy
%O A189318 0,1
%A A189318 _L. Edson Jeffery_, Apr 20 2011