321

321 is a natural number that comes after 320 and before 322. It is an odd composite number whose prime factorization is 3 × 107. The digits sum to 6, so the number is divisible by 3. It is not a prime, square, or cube. As the product of two primes, it is a semiprime.

In various numeral systems, 321 is represented as CCCXXI in Roman numerals, 101000001 in binary, 0x141 in hexadecimal, and 0o501 in octal.

Common uses include the association with countdowns such as 3-2-1; area code 321 serves parts of Florida, including the Space Coast region surrounding Cape Canaveral and the Kennedy Space Center. In 321 CE, the Roman Emperor Constantine the Great issued an edict that Sunday be observed as a day of rest in the cities of the Empire.

Overall, 321 is a relatively simple integer with straightforward factorization and familiar representations in multiple bases, while also appearing in cultural references such as countdowns and regional dialing codes.