Fatto generale: 811 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Fatto matematico: 811 is the smallest prime factor of 24!.
Trivia: 811 is an uninteresting number.
Data storica: March 21st is the day in 1921 that the New Economic Policy is implemented by the Bolshevik Party in response to the economic failure as a result of War Communism.