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A188128 Expansion of (4-6*x-6*x^2+x^3)/((1+x)*(1-3*x+x^3)). 1
4, 2, 10, 23, 70, 197, 571, 1640, 4726, 13604, 39175, 112796, 324787, 935183, 2692756, 7753478, 22325254, 64283003, 185095534, 532961345, 1534601035, 4418707568, 12723161362, 36634883048, 105485941579, 303734663372, 874569107071 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

COMMENTS

Let A_{9,3} = [0,0,0,1; 0,0,1,1; 0,1,1,1; 1,1,1,1], a unit-primitive matrix (see [Jeffery]). Then a(n) = Trace([A_{9,3}]^n).

LINKS

Table of n, a(n) for n=0..26.

L. E. Jeffery, Unit-primitive matrices

Index entries for linear recurrences with constant coefficients, signature (2, 3, -1, -1).

FORMULA

G.f.: (4-6*x-6*x^2+x^3)/((1+x)*(1-3*x+x^3)).

a(n) = 2*a(n-1)+3*a(n-2)-a(n-3)-a(n-4), {a(m)}={4,2,10,23}, m=0,1,2,3.

a(n) = Sum_{k=1..4} ((x_k)^3-2*(x_k))^n, x_k=2*(-1)^(k-1)*cos(k*Pi/9).

a(n) = (-1)^n+(1+2*cos(Pi/9))^n+(1-cos(Pi/9)+sqrt(3)*sin(Pi/9))^n + (1-cos(Pi/9)-sqrt(3)*sin(Pi/9))^n. - L. Edson Jeffery, Dec 15 2011

a(n) = (-1)^n + 3*A147704(n). - R. J. Mathar, Oct 08 2016

MATHEMATICA

CoefficientList[Series[(4-6x-6x^2+x^3)/((1+x)(1-3x+x^3)), {x, 0, 30}], x] (* or *) LinearRecurrence[{2, 3, -1, -1}, {4, 2, 10, 23}, 30] (* Harvey P. Dale, Apr 22 2011 *)

CROSSREFS

Sequence in context: A128781 A135440 A215500 * A336914 A091484 A163544

Adjacent sequences:  A188125 A188126 A188127 * A188129 A188130 A188131

KEYWORD

nonn,easy

AUTHOR

L. Edson Jeffery, Apr 05 2011

STATUS

approved

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Last modified June 19 05:18 EDT 2021. Contains 345125 sequences. (Running on oeis4.)