General fact: 24 is the number of letters in both the modern and classical Greek alphabet.
Mathematical fact: 24 is the largest integer that is evenly divisible by all natural numbers no larger than its square root.
Trivia: 24 is the number of hours in a day.
Historical date: 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).