Where to find it:

NodeGraph / Right Mouse Click / Add Nodes / Math / Extension Pack / A /

atanh returns the arc hyperbolic tangent of x; the inverse of tanh. The result is undefined if |x|>1.

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/atanh.xhtml

•X

Specify the value whose arc hyperbolic tangent to return.

•Output RGB

Separate computation for Input Channels Red, Green, Blue with an Alpha Channel of 1.0

•R

Computation for Input Red channel only, saved into R, G and B channel with an Alpha of 1.0

•G

Computation for Input Green channel only, saved into R, G and B channel with an Alpha of 1.0

•B

Computation for Input Blue channel only, saved into R, G and B channel with an Alpha of 1.0

•A

Computation for Input Alpha channel only, saved into R, G and B channel with an Alpha of 1.0