Fatto generale: 21855 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21855 is an uninteresting number.
Trivia: 21855 is an unremarkable number.
Data storica: November 1st is the day in 1765 that the British Parliament enacts the Stamp Act on the 13 colonies in order to help pay for British military operations in North America.