general_fact: 15968 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 15968 is an unremarkable number.
trivia: 15968 is an unremarkable number.
historical_date: September 19th is the day in 1961 that Betty and Barney Hill claim that they saw a mysterious craft in the sky and that it tried to abduct them.