ArcSech[z] == I (2 UnitStep[Im[1/z]] - 1) (Pi - Sqrt[2] Sqrt[-z - 1] HypergeometricPFQ[{{3/2}, {1/2}, {1/2}}, {{}, {3/2}, {3/2}}, -1, z + 1]) /; !IntervalMemberQ[Interval[{0, 1}], z]

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2001-10-29