A common mistake popped up in the original writeup:
Swedish and Icelandic patronymics end with -son, Danish and Norwegian are the ones ending with -sen.
Nordic surnames of this kind used to be "real" patronymics, so if a man named "Johan Eriksson" had a son named "Lars", the son's full name would be "Lars Johansson", i.e. "Lars, Johan's son". The extra "s" identifies the name as Nordic, since Anglo-Saxon surnames ending in -son usually only have one "s", e.g. "Johnson". Since the practice of using patronymics ended in Sweden during the 19:th century, many of the old names got changed, so there are Swedes called "Erikson" or even "Erixon" as well...