\[\operatorname{arccosh}z=\ln\left(2z\right)-\frac{1}{2}\frac{1}{2z^{2}}-\frac{1%
\cdot 3}{2\cdot 4}\frac{1}{4z^{4}}-\frac{1\cdot 3\cdot 5}{2\cdot 4\cdot 6}%
\frac{1}{6z^{6}}-\cdots,\]