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A012464
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arctanh(arctan(x)*arctan(x))=2/2!*x^2-16/4!*x^4+608/6!*x^6-43776/8!*x^8...
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0
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0, 2, -16, 608, -43776, 5490432, -1043742720, 281302333440, -101944270848000, 47833801306275840, -28212954337286553600, 20432760600063600230400, -17826780360146975037849600, 18441699370235590444905922560
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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) ~ (-1)^(n+1) * (2*n-1)! * ((exp(2)+1)/(exp(2)-1))^(2*n). - Vaclav Kotesovec, Feb 08 2015
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MATHEMATICA
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nn = 20; Table[(CoefficientList[Series[ArcTanh[ArcTan[x]^2], {x, 0, 2*nn}], x] * Range[0, 2*nn]!)[[n]], {n, 1, 2*nn+1, 2}] (* Vaclav Kotesovec, Feb 08 2015 *)
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CROSSREFS
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KEYWORD
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sign
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AUTHOR
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Patrick Demichel (patrick.demichel(AT)hp.com)
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EXTENSIONS
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STATUS
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approved
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