Fatto matematico: 1851 is the number of inequivalent asymmetric Ferrers graphs with 28 points.
Trivia: 1851 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Data storica: January 24th is the day in 1918 that the Gregorian calendar is introduced in Russia by decree of the Council of People's Commissars effective February 14(NS).