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

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2001-10-29