Upon arrival in Norway

In Norway, you must have a National ID number. You can read more about this on the below link.

https://www.skatteetaten.no/en/International-pages/Felles-innhold-benyttes-i-flere-malgrupper/Articles/Norwegian-national-ID-numbers/

Key things to highlight is:
If you intend to stay in Norway for more than six months, you must apply for a National ID number. First a D-number will be allocated as a temporarily ID number. Then after 6 months in Norway, you can apply for the Norwegian National ID (person nummer). It is important to know that you must report the move to Norway as soon as possible upon arrival, as it is this date that determines when 6 months has been reached and you can apply for the National ID. It is also important to be aware of that the D- number does not give you the same rights/opportunities as a National ID number as for example; signing a mobile contract, applying for a mortgage, register a car in your name amongst other things. Consequently this is good to consider when you are planning the move and deciding on things like; housing (whether to buy or rent) and where to live (far from work, in close proximity to public transport) etc.