General fact: 21073 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 21073 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 21073 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Historical date: September 10th is the day in 1932 that the New York City Subway's third competing subway system, the municipally-owned IND, is opened.