CXXXIX is the Roman numeral representation for the number 139. Roman numerals are a numeral system originating from ancient Rome, using combinations of letters from the Latin alphabet. In this system, "C" stands for 100, "X" for 10, and "IX" represents 9, which together add up to 139. The number 139 can also be found in various contexts, such as in mathematics, where it is classified as a prime number. This means it is only divisible by 1 and itself. Additionally, 139 is often used in literature, history, and even in the identification of specific items, like bus routes or area codes.