Where does “trettan” come from?

trettan (Norwegian Nynorsk) comes from Old Norse þrettán, from Proto-Germanic þritehun, from Proto-Germanic tehun, from Proto-Indo-European déḱm̥t — ten.

Ancestry of “trettan”, step by step

StepLanguageWordMeaning
1Old Norseþrettánthirteen
2Proto-Germanicþritehunthirteen
3Proto-Germanictehunten
4Proto-Indo-Europeandéḱm̥tten
Every word from Proto-Indo-European déḱm̥t →Every word from Proto-Germanic tehun →Every word from Proto-Germanic þritehun →