Double <i>SO</i>(2,1)-integrals and formulas for Whittaker functions
With the help of some double integral bilinear functionals with homogeneous kernels defined on a pair of representation spaces of the group <i>SO</i>(2,1) we obtain some functional relations for Whittaker functions and calculate the sum of one series of Gauss hypergeometric functions converging to a Whittaker function.