Fatto generale: 21724 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21724 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 21724 is a boring number.
Data storica: June 23rd is the day in 1757 that Battle of Plassey – 3,000 British troops under Robert Clive defeat a 50,000 strong Indian army under Siraj Ud Daulah at Plassey.