Area code 521 is not assigned to any specific region in North America. The North American Numbering Plan (NANP) includes area codes from 200 to 999, but 521 is not in use for any specific area.
It is possible that it could be a special-purpose or temporary code, or it might be reserved for future use. If you’re seeing an area code 521 in a phone number, it might be worth verifying whether it’s legitimate or if it could be part of an international dialing scheme.
