309

309 is a natural number that comes after 308 and before 310. In arithmetic terms, it is an odd composite number with the prime factorization 3 × 103, so it is classified as a semiprime. Its positive divisors are 1, 3, 103, and 309.

In various numeral systems, 309 has distinct representations. In binary it is 100110101, in hexadecimal it is 0x135, and in base 3 it is 102110. In Roman numerals, 309 is written as CCCIX. The sum of its decimal digits is 12, which makes 309 divisible by 3.

The number 309 appears in several practical contexts. In North American telephone numbering, 309 is an area code used for parts of central Illinois. The number is also used in road and highway designations in different countries, where a route simply carries the number 309.

From a mathematical standpoint, 309 is the product of two primes, 3 and 103, which gives it a relatively simple factor structure compared with many larger integers. It is not a square or a cube, and it does not belong to several common special-number sequences. As a member of the integers, 309 participates in standard arithmetic operations and serves as a representative example of a small semiprime.