809

809 is a natural number that follows 808 and precedes 810. In mathematics, 809 is a prime number. It is odd and not divisible by any number other than 1 and itself; its square root is about 28.5, so a quick check against primes up to 23 confirms its primality. In Roman numerals, 809 is written as DCCCIX.

In telecommunication, 809 is known as an area code used in the Dominican Republic within the North American Numbering Plan. It originally covered the country and, with overlays, now exists alongside 829 and 849. When dialing from outside the NANP, Dominican Republic numbers with area code 809 are accessed as +1 809 xxx xxxx, with the remaining digits forming the local number.

Historically, 809 also designates the year 809 CE in the Gregorian calendar, a point in the early medieval period. As a numeral, 809 appears in various systems and contexts, but its primary contemporary associations are as a prime number and as an area code within the Dominican Republic.