Fatto matematico: 8641 is the number of ways to tile a 3×25 rectangle with 3×1 rectangles.
Trivia: 8641 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: August 28th is the day in 663 that Silla–Tang armies crush the Baekje restoration attempt and force Yamato Japan to withdraw from Korea in the Battle of Baekgang.