Mathematical fact: 2120 is the number of ways to stack 16 pennies in a line so that each penny lies on the table or on two pennies.
Trivia: 2120 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Historical date: October 20th is the day in 1976 that the ferry George Prince is struck by a ship while crossing the Mississippi River between Destrehan and Luling, Louisiana.