Fatto generale: 1617 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 1617 is the maximum value of n so that there exist 6 denominations of stamps so that every postage from 1 to n can be paid for with at most 9 stamps.
Trivia: 1617 is an unremarkable number.
Data storica: June 4th is the day in 1996 that the first flight of Ariane 5 explodes after roughly 20 seconds.