Fatto matematico: 1521 is the smallest number that can be written as the sum of 4 distinct cubes in 3 ways.
Trivia: 1521 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: February 29th is the day in 1796 that the Jay Treaty between the United States and Great Britain comes into force, facilitating ten years of peaceful trade between the two nations.