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A012181
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arctanh(tan(arctanh(x))) = x + (6/3!)*x^3 + (184/5!)*x^5 + 13360/7!*x^7 + ...
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0
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1, 6, 184, 13360, 1770880, 373587200, 115086003200, 48784879769600, 27245388132352000, 19392357120188416000, 17137521906875269120000, 18411376349575875461120000, 23632217190341837269237760000, 35718167409293109428879360000000
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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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MAPLE
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a:= n-> (t-> t!*coeff(series(arctanh(tan(arctanh(x))), x, t+1), x, t))(2*n+1):
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MATHEMATICA
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nn = 20; Table[(CoefficientList[Series[ArcTanh[Tan[ArcTanh[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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