Fatto generale: 641 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 641 is the smallest prime factor of 2^{2^{5}}+1.
Trivia: 641 is an uninteresting number.
Data storica: October 2nd is the day in 1970 that a plane carrying the Wichita State University football team, administrators, and supporters crashes in Colorado killing 31 people.