general_fact: 1668 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 1668 is the maximum number of regions space can be divided into by 18 spheres.
trivia: 1668 is an uninteresting number.
historical_date: July 25th is the day in 1965 that Bob Dylan goes electric as he plugs in at the Newport Folk Festival, signaling a major change in folk and rock music.