Based on successive correction method, we have solved LSS equation numerically and calculated the range statistic parameters Rp,△Rp and R⊥ for ions implanted in GaAs. We propose simple formulas for initial values in calculating Rp,△Rp and R⊥; by using these formulas, the zero-energy divergence can be avoided and sufficient accuracy achieved. The expressions for β-integration are given to save computation time. Our numerical method and computer program can also be used to other ion-target systems.