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A098456
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Expansion of 1/sqrt(1-4x-64x^2).
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0
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1, 2, 38, 212, 2566, 20092, 210524, 1884136, 18854854, 178415852, 1764019828, 17115907096, 169100140444, 1661540282456, 16458178007288, 162887627833552, 1618680238292294, 16095872154638156, 160435286115927044
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| Define Q(n,x)=sum{k=0..floor(n/2), binomial(n,k)binomial(2(n-k),n)x^(n-2k)}. Then a(n)=4^n*Q(n,1/4). Central coefficients of (1+2x+17x^2)^n.
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FORMULA
| E.g.f.: exp(2x)BesselI(0, 2sqrt(17)x); a(n)=sum{k=0..floor(n/2), binomial(n, k)binomial(2(n-k), n)16^k}.
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MATHEMATICA
| CoefficientList[Series[1/Sqrt[1-4x-64x^2], {x, 0, 30}], x] (* From Harvey P. Dale, Dec 27 2011 *)
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CROSSREFS
| Cf. A084770, A098455.
Sequence in context: A075459 A050248 A105645 * A179503 A126731 A046845
Adjacent sequences: A098453 A098454 A098455 * A098457 A098458 A098459
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Sep 08 2004
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