Can I register a domain name with special Norwegian characters?
Yes, you can.
Can I register domain names with only one character?
The .no domain name policy does not allow domain names with only one character. There are several reasons for this. The likelihood of typing errors is higher when there is only one character (this is why the top level domain in Norway is .no and not .n). Another reason is that these names are a limited resource and are therefore held back in case it is necessary to expand the name space at a later point in time.