Mathematical fact: 9748 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 14 stamps.
Trivia: 9748 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Historical date: September 8th is the day in 1966 that the Severn Bridge is officially opened by Queen Elizabeth II.