general_fact: 2131 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 2131 is the number of domino tilings of a 3×12 rectangle.
trivia: 2131 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
historical_date: October 31st is the day in 2003 that a bankruptcy court approves MCI's reorganization plans, essentially clearing the telecommunications company to exit bankruptcy.