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A063757
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G.f.: (1+3*x+2*x^2)/((1-x)*(1-2*x^2)).
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3
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1, 4, 8, 14, 22, 34, 50, 74, 106, 154, 218, 314, 442, 634, 890, 1274, 1786, 2554, 3578, 5114, 7162, 10234, 14330, 20474, 28666, 40954, 57338, 81914, 114682, 163834, 229370, 327674, 458746, 655354, 917498, 1310714, 1835002, 2621434
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OFFSET
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0,2
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REFERENCES
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P. de la Harpe, Topics in Geometric Group Theory, Univ. Chicago Press, 2000, p. 158.
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LINKS
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FORMULA
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a(0)=1, a(1)=4, a(2)=8, a(n)=a(n-1)+2*a(n-2)-2*a(n-3) From Harvey P. Dale, Jun 05 2012
a(n)=2^((n-3)/2)*((5*Sqrt[2]-7)*(-1)^n+7+5*Sqrt[2])-6 From Harvey P. Dale, Jun 05 2012
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MATHEMATICA
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CoefficientList[Series[(1+3x+2x^2)/((1-x)(1-2x^2)), {x, 0, 40}], x] (* or *) LinearRecurrence[{1, 2, -2}, {1, 4, 8}, 41] (* Harvey P. Dale, Jun 05 2012 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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