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A091096
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Expansion of (1+5x-40x^2)/((1-5x)(1+5x)).
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0
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1, 5, -15, 125, -375, 3125, -9375, 78125, -234375, 1953125, -5859375, 48828125, -146484375, 1220703125, -3662109375, 30517578125, -91552734375, 762939453125, -2288818359375, 19073486328125, -57220458984375, 476837158203125, -1430511474609375
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OFFSET
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0,2
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COMMENTS
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a(0)=1, a(2n-1)=k^(2n-1), a(2n)=(2-k)k^(2n-1), k=5; G.f.: (1+kx+(2-2k)kx^2)/((1-kx)(1+kx)), k=5.
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LINKS
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FORMULA
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a(n)=5^n/5 +(-4)(-5)^n/5+8*0^n/5
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MATHEMATICA
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CoefficientList[Series[(1+5x-40x^2)/((1-5x)(1+5x)), {x, 0, 30}], x] (* or *) LinearRecurrence[{0, 25}, {1, 5, -15}, 30] (* Harvey P. Dale, Dec 26 2015 *)
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CROSSREFS
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KEYWORD
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easy,sign
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AUTHOR
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STATUS
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approved
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