general_fact: 81881 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 81881 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
trivia: 81881 is an uninteresting number.
historical_date: March 7th is the day in 2009 that the Kepler space observatory, designed to discover Earth-like planets orbiting other stars, is launched.