Fatto generale: 21628 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21628 is an uninteresting number.
Trivia: 21628 is an unremarkable number.
Data storica: March 19th is the day in 1916 that Eight American planes take off in pursuit of Pancho Villa, the first United States air-combat mission in history.