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 a boring number.
historical_date: July 25th is the day in 1909 that Louis Blériot makes the first flight across the English Channel in a heavier-than-air machine from (Calais to Dover) in 37 minutes.