Fait général: 9855 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 9855 is a rhombic dodecahedral number.
Culture générale: 9855 is an unremarkable number.
Date historique: December 24th is the day in 563 that the Byzantine church Hagia Sophia in Constantinople is dedicated for the second time after being destroyed by earthquakes.