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A189317 Expansion of 5*(1-6*x+x^2)/(1-10*x+5*x^2) 4

%I

%S 5,20,180,1700,16100,152500,1444500,13682500,129602500,1227612500,

%T 11628112500,110143062500,1043290062500,9882185312500,93605402812500,

%U 886643101562500,8398404001562500,79550824507812500,753516225070312500,7137408128164062500

%N Expansion of 5*(1-6*x+x^2)/(1-10*x+5*x^2)

%C (Start) Let A be the unit-primitive matrix (see [Jeffery])

%C A=A_(10,3)=

%C (0 0 0 1 0)

%C (0 0 1 0 1)

%C (0 1 0 2 0)

%C (1 0 2 0 1)

%C (0 2 0 2 0).

%C Then a(n)=Trace(A^(2*n)). (End)

%C Evidently one of a class of accelerator sequences for Catalan's constant based on traces of successive powers (here they are A^(2*n)) 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 L. E. Jeffery, <a href="/wiki/User:L._Edson_Jeffery/Unit-Primitive_Matrices">Unit-primitive matrices</a>.

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (10, -5).

%F G.f.: 5*(1-6*x+x^2)/(1-10*x+5*x^2).

%F a(n)=10*a(n-1)-5*a(n-2), n>2, a(0)=5, a(1)=20, a(2)=180.

%F a(n)=Sum_{k=1..5) ((w_k)^3-2*w_k)^(2*n), w_k=2*cos((2*k-1)*Pi/10).

%F a(n)=2*((5-2*Sqrt(5))^n+(5+2*Sqrt(5))^n), for n>0, with a(0)=5.

%t CoefficientList[Series[5*(1-6x+x^2)/(1-10x+5x^2),{x,0,30}],x] (* or *) Join[ {5},LinearRecurrence[{10,-5},{20,180},30]] (* _Harvey P. Dale_, Apr 02 2013 *)

%o (PARI) Vec(5*(1-6*x+x^2)/(1-10*x+5*x^2)+O(x^99)) \\ _Charles R Greathouse IV_, Sep 25 2012

%Y A189315, A189316, A189318.

%K nonn,easy

%O 0,1

%A _L. Edson Jeffery_, Apr 20 2011

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Last modified July 20 22:54 EDT 2019. Contains 325189 sequences. (Running on oeis4.)