general_fact: 2017 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 2017 is a value of n for which f(n) = f(n-1) + f(n-2).
trivia: 2017 is an uninteresting number.
historical_date: July 9th is the day in 1776 that George Washington ordered the Declaration of Independence to be read out loud to members of the Continental Army in New York City for the first time.