  We have constructed a sequence of solutions of the Helmholtz equation forming
an orthogonal sequence on a given surface. Coefficients of these functions
depend on an explicit algebraic formulae from the coefficient of the surface.
Moreover, for exterior Helmholtz equation we have constructed an explicit
normal derivative of the Dirichlet Green function. In the same way the
Dirichlet-to-Neumann operator is constructed. We proved that normalized
coefficients are uniformly bounded from zero.
