Coulomb Energy Averaged over the nell^N-Atomic States with a Definite Spin

A purely group-theoretical approach (for which the symmetric group plays a central r\^ole), based upon the use of properties of fractional-parentage coefficients and isoscalar factors, is developed for the derivation of the Coulomb energy averaged over the states, with a definite spin, arising from an atomic configuration $n \ell^N$.