general_fact: 21141 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 21141 is an uninteresting number.
trivia: 21141 is an uninteresting number.
historical_date: November 17th is the day in 1855 that David Livingstone becomes the first European to see the Victoria Falls in what is now present-day Zambia-Zimbabwe.