Fatto generale: 6663 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 6663 is a value of n for which s(n) is a repdigit.
Trivia: 6663 is an unremarkable number.
Data storica: March 29th is the day in 1971 that a Los Angeles, California jury recommends the death penalty for Charles Manson and three female followers.