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A081920
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Expansion of exp(2x)/sqrt(1-x^2).
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4
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1, 2, 5, 14, 49, 202, 1069, 6470, 48353, 391058, 3767029, 37936318, 445650385, 5359634906, 74198053661, 1036667808758, 16516851030721, 262805595346210, 4735033850606437, 84510767762583662, 1698609728377283441
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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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E.g.f. exp(2x)/sqrt(1-x^2).
Conjecture: a(n) -2*a(n-1) -(n-1)^2*a(n-2) +2*(n-1)*(n-2)*a(n-3)=0. - R. J. Mathar, Nov 24 2012
Conjecture confirmed using d.e. (x^2-1)*y' + (-2*x^2+x+2)*y = 0 satisfied by the E.g.f. - Robert Israel, Feb 19 2018
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MAPLE
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f:= gfun:-rectoproc({a(n) -2*a(n-1) -(n-1)^2*a(n-2) +2*(n-1)*(n-2)*a(n-3)=0, a(0)=1, a(1)=2, a(2)=5}, a(n), remember):
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MATHEMATICA
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CoefficientList[Series[E^(2*x)/Sqrt[1-x^2], {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Feb 04 2014 *)
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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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