general_fact: 15815 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 15815 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
trivia: 15815 is an unremarkable number.
historical_date: April 19th is the day in 1892 that Charles Duryea claims to have driven the first automobile in the United States, in Springfield, Massachusetts.