general_fact: 12721 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 12721 is an unremarkable number.
trivia: 12721 is an uninteresting number.
historical_date: October 29th is the day in 312 that Constantine the Great enters Rome after his victory at the Milvian Bridge, stages a grand adventus in the city, and is met with popular jubilation.