General fact: 91931 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 91931 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Trivia: 91931 is a boring number.
Historical date: September 12th is the day in 1940 that an explosion at the Hercules Powder Company plant in Kenvil, New Jersey kills 51 people and injures over 200.