Fatto matematico: 8669 is the maximum value of n so that there exist 5 denominations of stamps so that every postage from 1 to n can be paid for with at most 18 stamps.
Trivia: 8669 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: September 25th is the day in 2008 that China launches the spacecraft Shenzhou 7.