A Norwegian company has two numbers that are often confused: the organisation number and the VAT number. They are closely related, but they do not mean the same thing, and only one of them is held by everyone.
The organisation number
Nine digits, assigned by the Central Coordinating Register on registration. It never changes, and it is not given to anyone else after the entity is deleted. Every registered entity has one: limited companies, sole proprietorships, associations, foundations, municipalities.
The last digit is a check digit computed with modulus 11. That means a mistyped number can be rejected without any lookup at all — roughly nine in ten random nine-digit numbers are invalid.
The VAT number
The VAT number is not a new number. It is the organisation number with the letters MVA after it: 999 999 999 MVA. Written internationally, NO goes in front.
The difference is who has one. Registration becomes compulsory only once VAT-liable turnover passes NOK 50,000 in a twelve-month period. Below that threshold the company exists in the main register but not the VAT Register — and must not invoice with VAT.
Why VIES will not help you here
If you are coming from the EU, the reflex is to check the number in VIES. It does not work. VIES validates VAT numbers issued by EU member states, and Norway is not one. A Norwegian VAT number simply is not in that service — a negative answer there does not mean the company is unregistered.
The right source is the Central Coordinating Register, which states both whether the entity is in the VAT Register and from what date.
The practical check
Look up the organisation number. Confirm the name matches what is on the invoice, that the company is active, and — if the invoice charges VAT — that it is actually VAT-registered. Three facts, one lookup.