general_fact: 21907 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 21907 is an unremarkable number.
trivia: 21907 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
historical_date: December 23rd is the day in 2003 that PetroChina Chuandongbei natural gas field explosion, Guoqiao, Kai County, Chongqing, China, killing at least 234.