Fait général: 9421 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fait mathématique: 9421 is a value of n for which n and 8n together use each digit 1-9 exactly once.
Culture générale: 9421 is an uninteresting number.
Date historique: October 16th is the day in 1846 that William TG Morton first demonstrated ether anesthesia at the Massachusetts General Hospital in the Ether Dome.