313

313 is a natural number that follows 312 and precedes 314. In decimal notation it is a three-digit palindrome, consisting of the digits 3–1–3. It is a prime number, having no positive divisors other than 1 and itself. In Roman numerals it is written as CCCXIII. In binary it is 100111001, and in hexadecimal it is 0x139. As a prime congruent to 1 modulo 4, 313 can be expressed as a sum of two squares: 12^2 + 13^2.

In historical chronology, the year 313 CE is notable for the Edict of Milan, issued by Emperor Constantine I and Licinius, which proclaimed religious tolerance for Christians within the Roman Empire and marked a turning point in the history of early Christianity.

In contemporary usage, 313 is the area code for Detroit, Michigan, and the surrounding region in the United States. The code is closely associated with the city and is frequently used in popular culture and local branding to refer to Detroit. The number appears in various contexts as a shorthand reference to the area.

Beyond these uses, 313 can be found in mathematical discussions as an example of a prime that is the sum of two squares, as well as in numeral representation exercises related to conversions between bases and numeral systems.