Fatto generale: 21853 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21853 is an uninteresting number.
Trivia: 21853 is an unremarkable number.
Data storica: October 30th is the day in 1918 that the Ottoman Empire signs an armistice with the Allies, ending the First World War in the Middle East.