Fait général: 2535 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 2535 is the number of ways to 13-color the faces of a tetrahedron.
Culture générale: 2535 is a boring number.
Date historique: December 9th is the day in 1979 that the eradication of the smallpox virus is certified, making smallpox the first and to date only human disease driven to extinction.