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A012818
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arctanh(sec(x)*sinh(x))=x+6/3!*x^3+140/5!*x^5+8456/7!*x^7...
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0
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1, 6, 140, 8456, 957840, 174293856, 46514037440, 17115342333056, 8304761365213440, 5137820023434733056, 3947233200665413667840, 3686931444647916864505856, 4114664615209642258282352640
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) ~ (2*n)! / r^(2*n+1), where r = 0.7032906588639654058999212003816567397131... is the root of the equation sec(r)*sinh(r) = 1. - Vaclav Kotesovec, Feb 05 2015
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MATHEMATICA
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nn = 20; Table[(CoefficientList[Series[ArcTanh[Sec[x]*Sinh[x]], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* Vaclav Kotesovec, Feb 05 2015 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Patrick Demichel (patrick.demichel(AT)hp.com)
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STATUS
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approved
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