General fact: 84 is the code for international direct dial phone calls to Vietnam.
Mathematical fact: 84 is the sum of the first seven triangular numbers (making it a tetrahedral number), as well as the sum of a twin prime (41 + 43).
Trivia: 84 is the atomic number of polonium.
Historical date: March 24th is the day in 1973 that Kenyan athlete Kip Keino defeats Jim Ryun at the first-ever professional track meet in Los Angeles, California.