Fatto generale: 21064 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21064 is an uninteresting number.
Trivia: 21064 is a boring number.
Data storica: September 1st is the day in 1878 that Emma Nutt becomes the world's first female telephone operator when she is recruited by Alexander Graham Bell to the Boston Telephone Dispatch Company.