Fatto matematico: 5739 is a value of n for which 5n and 7n together use each digit exactly once.
Trivia: 5739 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: September 17th is the day in 1462 that the Battle of Świecino (also known as the Battle of Żarnowiec) is fought during Thirteen Years' War.