general_fact: 1640 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
math_fact: 1640 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
trivia: 1640 is an uninteresting number.
historical_date: June 27th is the day in 1991 that Slovenia, after declaring independence two days before is invaded by Yugoslav troops, tanks, and aircraft starting the Ten-Day War.