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A098575
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a(n) = Sum_{k=0..floor(n/4)} C(n-2*k,2*k)*2^k.
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4
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1, 1, 1, 1, 3, 7, 13, 21, 35, 63, 117, 213, 379, 671, 1197, 2149, 3859, 6911, 12357, 22101, 39563, 70847, 126845, 227045, 406371, 727391, 1302101, 2330901, 4172443, 7468767, 13369293, 23931621, 42838835, 76683583, 137266917, 245713493
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OFFSET
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0,5
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LINKS
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FORMULA
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G.f.: (1-x)/((1-x)^2-2*x^4).
a(n) = 2*a(n-1) - a(n-2) + 2*a(n-4).
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MATHEMATICA
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CoefficientList[Series[(1-x)/((1-x)^2-2x^4), {x, 0, 40}], x] (* Vincenzo Librandi, Jun 17 2012 *)
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PROG
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(Magma) I:=[1, 1, 1, 1]; [n le 4 select I[n] else 2*Self(n-1)-Self(n-2)+2*Self(n-4): n in [1..40]]; // Vincenzo Librandi, Jun 17 2012
(PARI) x='x+O('x^30); Vec((1-x)/((1-x)^2-2*x^4)) \\ G. C. Greubel, Feb 03 2018
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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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