Fait général: 4121 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 4121 is a number whose product of digits is equal to its sum of digits.
Culture générale: 4121 is a boring number.
Date historique: April 13th is the day in 1987 that Portugal and the People's Republic of China sign an agreement in which Macau would be returned to China in 1999.