  The note is aimed at giving a complete characterization of the following
equation: $$\displaystyle
p\frac{\Gamma(\frac{n}{2}-\frac{s}{p-1})\Gamma(s+\frac{s}{p-1})}{\Gamma(\frac{s}{p-1})\Gamma(\frac{n-2s}{2}-\frac{s}{p-1})}
=\frac{\Gamma(\frac{n+2s}{4})^2}{\Gamma(\frac{n-2s}{4})^2}.$$
  The method is based on some key transformation and the properties of the
Gamma function. Applications to fractional nonlinear Lane-Emden equations will
be given.
