general_fact: 16943 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 16943 is an unremarkable number.
trivia: 16943 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
historical_date: May 21st is the day in 2010 that JAXA, the Japan Aerospace Exploration Agency, launches the solar-sail spacecraft IKAROS aboard an H-IIA rocket.