Fatto generale: 6991 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 6991 is a value of n for which reverse(f(n)) = f(reverse(n)).
Trivia: 6991 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: February 20th is the day in 1933 that the Congress of the United States proposes the Twenty-first Amendment to the United States Constitution that will end Prohibition in the United States.