Fait général: 21751 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 21751 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Culture générale: 21751 is an uninteresting number.
Date historique: July 20th is the day in 1960 that the Polaris missile is successfully launched from a submarine, the USS George Washington, for the first time.