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A087944
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Expansion of (1-4*x+3*x^2)/((1-2*x)*(1-4*x+x^2)).
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6
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1, 2, 6, 20, 70, 252, 922, 3404, 12630, 46988, 175066, 652764, 2434966, 9085052, 33901146, 126511340, 472127830, 1761967212, 6575675482, 24540603644, 91586476950, 341804779868, 1275631593946, 4760719498764, 17767242206806
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OFFSET
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0,2
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COMMENTS
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LINKS
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FORMULA
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a(0)=1, a(2)=2, a(2)=6, a(n) = 6*a(n-1)-9*a(n-2)+2*a(n-3), n>2.
a(n) = (2^n+(2+sqrt(3))^n+(2-sqrt(3))^n)/3.
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MATHEMATICA
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CoefficientList[Series[(1-4x+3x^2)/((1-2x)(1-4x+x^2)), {x, 0, 30}], x] (* or *) LinearRecurrence[{6, -9, 2}, {1, 2, 6}, 30] (* Harvey P. Dale, Feb 09 2013 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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