Fait général: 1521 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 1521 is the smallest number that can be written as the sum of 4 distinct cubes in 3 ways.
Culture générale: 1521 is an uninteresting number.
Date historique: February 29th is the day in 1504 that Christopher Columbus uses his knowledge of a lunar eclipse that night to convince Native Americans to provide him with supplies.