Fatto generale: 6537 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 6537 is the smallest value of n for which the numbers n-6 through n+6 can not be written as the sum of 2 squares.
Trivia: 6537 is an unremarkable number.
Data storica: November 23rd is the day in 1976 that Apneist Jacques Mayol is the first man to reach a depth of 100 m undersea without breathing equipment.