Physical Review A
Bethe logarithms accurate to 14 or 15 places to the right of the decimal are tabulated for all states of hydrogen up to n=20. Approximation methods for Rydberg states of two-electron atoms are discussed. © 1990 The American Physical Society.
Drake, Gordon W. F. and Swainson, R. A.. (1990). Bethe logarithms for hydrogen up to n=20, and approximations for two-electron atoms. Physical Review A, 41 (3), 1243-1246.