Fait mathématique: 9888 is the number of connected graphs with 8 vertices whose complements are also connected.
Culture générale: 9888 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Date historique: January 26th is the day in 1564 that the Council of Trent issues its conclusions in the Tridentinum, establishing a distinction between Roman Catholicism and Protestantism.