Fatto matematico: 1581 is the smallest number whose 8^{th} power contains exactly the same digits as another 8^{th} power.
Trivia: 1581 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: April 29th is the day in 1864 that Theta Xi fraternity is founded at Rensselaer Polytechnic Institute, the only fraternity to be founded during the Civil War.