arccosh⁡z=(2⁢(z-1))1/2⁢(1+∑n=1∞(-1)n⁢1⋅3⋅5⁢⋯⁢(2⁢n-1)22⁢n⁢n!⁢(2⁢n+1)⁢(z-1)n),