general_fact: 21457 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 21457 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
trivia: 21457 is a boring number.
historical_date: September 29th is the day in 522 BC that Darius I of Persia kills the Magian usurper Gaumâta, securing his hold as king of the Persian Empire.