general_fact: 7820 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 7820 is the Stirling number of the second kind S(17,15).
trivia: 7820 is an uninteresting number.
historical_date: May 29th is the day in 1919 that Albert Einstein's theory of general relativity is tested (later confirmed) by Arthur Eddington and Andrew Crommelin.