general_fact: 13537 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 13537 is a boring number.
trivia: 13537 is a boring number.
historical_date: January 22nd is the day in 1971 that the Singapore Declaration, one of the two most important documents to the uncodified constitution of the Commonwealth of Nations, is issued.