ArcTanh[z] == z/(1 - z^2 + ContinueFraction[ {2 z^2 Floor[(1 + k)/2] (2 Floor[(1 + k)/2] - 1), (1 + 2 k) (1 - (1/2) (1 + (-1)^k) z^2)}, {k, 1, Infinity}]) /; !IntervalMemberQ[Interval[{-Infinity, -1}], z] && !IntervalMemberQ[Interval[{1, Infinity}], z]

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2001-10-29