Hecho general: 84 is the atomic number of polonium.
Hecho matemático: 84 is also the lim sup of the largest finite subgroup of the mapping class group of a genus g surface divided by g.
Trivia: 84 is the code for international direct dial phone calls to Vietnam.
Fecha histórica: March 24th is the day in 1900 that Mayor of New York City Robert Anderson Van Wyck breaks ground for a new underground "Rapid Transit Railroad" that would link Manhattan and Brooklyn.