general_fact: 21066 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 21066 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
trivia: 21066 is an unremarkable number.
historical_date: September 3rd is the day in 1954 that the German U-Boat U-505 begins its move from a specially constructed dock to its final site at Chicago's Museum of Science and Industry.