Calculate the analytic core part of N-th moment of PSD without location parameter.
The analytic form uses Lihn function. The core part does not include the the beta polynomial
LihnBetaPoly) since it does not have a general analytic form.
A fully specified PSD S3 object
The N-th moment
Numeric value of the core part of the N-th moment
See Section "General Form of the N-th Moment" in the PSD paper