Universal Effective Quantum Number for Centrally Symmetric Problems

An effective quantum number determining with high accuracy the levels ordering in arbitrary centrally symmetric potentials for any space dimensionality is introduced and calculated by means of certain universal methods based on the known estimates for the total number of the bound states in the same potential for various dimensionality. Coincidence with some known exact results is demonstrated. The effective number is used for constructing the periodical system of the atomic electron shells.