Only organizations with a local presence in Norway and with registration in the Brønnøysund Register Centre are allowed to register domains under . Each organization can register 100 directly under the .no domain, but can register further domains under geographical domains or category second-level domains. Domain names must consist of 2 to 63 characters. Permitted characters are the lower-case English letters a through z, digits (0 through 9), the three Norwegian letter æ, ø and å, and 20 special Sami letters. Norid also maintains a series of second-level domains for geographic locations and special institutions. There is also a series of domain names that cannot be registered.