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The oscillator strength sums S (2), S (1), and S (−1) calculated using analytical Hartree–Fock wavefunctions and the sums S (−2) and S (−3) from an approximate uncoupled Hartree–Fock calculation are given for the atoms He to Kr. Trends are discussed as well as the accuracy of the Hartree–Fock calculations. An extensive compilation of accurate sums is used to assess the relative usefulness and accuracy of recently proposed bounds and approximations to the spherically averaged dispersion coefficient C6. Values of C6 for the first three rows are presented.