nObs we use direct results from Monte-Carlo simulation.
For higher nObs we use an approximation (based on Wilson-Hilferty transformation).Note that in R there is the numeric routine stats::qgamma which could also be used
as in stats::qgamma(p=.5, shape = 10, rate = 10) for n=10.
w1Fint(nObs)numeric. W1-value corrsponding to nObs. Same length as nObs
numeric. number of observations (vectorized)