Fatto generale: 66401 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 66401 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 66401 is an unremarkable number.
Data storica: October 18th is the day in 1945 that the USSR's nuclear program receives plans for the United States plutonium bomb from Klaus Fuchs at the Los Alamos National Laboratory.