Fatto generale: 11573 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 11573 is an uninteresting number.
Trivia: 11573 is a boring number.
Data storica: September 7th is the day in 1988 that Abdul Ahad Mohmand, the first Afghan in space, returns aboard the Soviet spacecraft Soyuz TM-5 after 9 days on the Mir space station.