9.103897(54)*10^-31 kg. Numbers in parentheses are approximations.
This is an obsolete version of A081801. The discrepancy is likely due to the fact that the accepted value for alpha, the fine structure constant (A005600), has changed significantly since the 1990's and this sequence uses a reference from that time period. - M. F. Hasler and Raphie Frank, Oct 27 2013
CRC Handbook for Chemistry and Physics, 75th edition, (1994-1995), Page 1-1.