Fait général: 8991 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 8991 is the smallest number so that it and its successor are both the product of a prime and the 5^{th} power of a prime.
Culture générale: 8991 is an unremarkable number.
Date historique: August 12th is the day in 1944 that Alençon is liberated by General Leclerc, the first city in France to be liberated from the Nazis by French forces.