Fatto generale: 5773 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 5773 is the index of a triangular number containing only 3 different digits.
Trivia: 5773 is a boring number.
Data storica: October 21st is the day in 1931 that the Sakurakai, a secret society in the Imperial Japanese Army, launches an abortive coup d'état attempt.