Fatto matematico: 657 is the number of ways to tile a 4×22 rectangle with 4×1 rectangles.
Trivia: 657 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: October 18th is the day in 1860 that the Second Opium War finally ends at the Convention of Peking with the ratification of the Treaty of Tientsin, an unequal treaty.