815

815 is a natural number that follows 814 and precedes 816. In mathematics, it is an odd composite number with prime factorization 5 × 163, making it a semiprime. It is not prime and not a square. The digit sum is 14, so it is not divisible by 3 or 9, and it is divisible by 5. In different bases, 815 is 1100101111 in binary and 0x32F in hexadecimal; in Roman numerals it is DCCCXV.

In historical terms, 815 can denote the year 815 CE, a point in the early medieval period within the broader context of the Carolingian Empire and its contemporaries.

As a geographic reference, 815 is an area code in northern Illinois, United States, used as part of the North American Numbering Plan. It originally covered a large portion of northern Illinois outside the Chicago area; an overlay code, 779, was introduced to expand number availability and is now used alongside 815 to serve the region, which includes cities such as Rockford and Joliet.