Fatto generale: 1581 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 1581 is the smallest number whose 8^{th} power contains exactly the same digits as another 8^{th} power.
Trivia: 1581 is an unremarkable number.
Data storica: April 29th is the day in 2004 that Dick Cheney and George W. Bush testify before the 9/11 Commission in a closed, unrecorded hearing in the Oval Office.