Fatto generale: 28708 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 28708 is an unremarkable number.
Trivia: 28708 is a boring number.
Data storica: August 6th is the day in 1787 that Sixty proof sheets of the Constitution of the United States are delivered to the Constitutional Convention in Philadelphia.