i'd learned from my norwegian relatives that you could tell if a person was swedish or norwegian by the way "son" was spelled on the end of their surname.
"sen" was norwegian, "son" was swedish.
Danes use "sen" as well. Swedes usually have an "s" in front of the "son". E.g., Danish: Larsen; Swedish: Larsson.
Just plain "son" is often English, e.g., Johnson, Peterson.