Fatto matematico: 993 is the number of paraffins with 8 carbon atoms.
Trivia: 993 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: September 19th is the day in 1971 that Montagnard troops of South Vietnam revolt against the rule of Nguyen Khanh, killing 70 ethnic Vietnamese soldiers.