general_fact: 1921 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 1921 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
trivia: 1921 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
historical_date: April 4th is the day in 1818 that the United States Congress adopts the flag of the United States with 13 red and white stripes and one star for each state (then 20).