[en] Ground state energies of helium - isoelectric series: He, Li+, B++, B+3 and C+4 were calculated by considering that the repulsive Coulomb interaction energy between the two electrons is described by the form 1/r12 only to a closely resemblance distance 2 R, and a constant potential within this distance. The results of calculations are in good agreement with the exact results of Pekeris. (author)