Fatto matematico: 7880 is the maximum value of n so that there exist 4 denominations of stamps so that every postage from 1 to n can be paid for with at most 26 stamps.
Trivia: 7880 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: July 28th is the day in 1957 that Heavy rain and a mudslide in Isahaya, western Kyūshū, Japan, kill 992.