Fait général: 4991 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 4991 is a Lucas-Carmichael number.
Culture générale: 4991 is an unremarkable number.
Date historique: August 30th is the day in 1800 that Gabriel Prosser postpones a planned slave rebellion in Richmond, Virginia, but is arrested before he can make it happen.