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A012152
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arctanh(tan(tan(x)))=x+6/3!*x^3+176/5!*x^5+12240/7!*x^7...
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0
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1, 6, 176, 12240, 1561088, 318007808, 94807748608, 38942692972544, 21088169713729536, 14558790290337431552, 12481351528273319821312, 13009249833253480856289280, 16200881782506627598590672896
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OFFSET
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0,2
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LINKS
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Table of n, a(n) for n=0..12.
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FORMULA
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a(n) ~ (2*n)! / (arctan(Pi/4))^(2*n+1). - Vaclav Kotesovec, Feb 05 2015
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MATHEMATICA
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nn = 20; Table[(CoefficientList[Series[ArcTanh[Tan[Tan[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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Sequence in context: A024277 A012177 A012227 * A165928 A024278 A062240
Adjacent sequences: A012149 A012150 A012151 * A012153 A012154 A012155
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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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