Fatto matematico: 4311 is the largest number n known with the property that n-2^{k} is a pseudoprime for all k>0.
Trivia: 4311 is an unremarkable number.
Data storica: October 20th is the day in 1991 that the Oakland Hills firestorm kills 25 and destroys 3,469 homes and apartments, causing more than $2 billion in damage.