General fact: 631 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 631 is an unremarkable number.
Trivia: 631 is an unremarkable number.
Historical date: September 22nd is the day in 1994 that the Nordhordland Bridge was opened across the Salhusfjorden between Klauvaneset and Flatøy in Hordaland, Norway.