Fatto generale: 21339 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 21339 is an unremarkable number.
Trivia: 21339 is a boring number.
Data storica: June 3rd is the day in 1973 that a Soviet supersonic Tupolev Tu-144 crashes near Goussainville, France, killing 14, the first crash of a supersonic passenger aircraft.