þreotene [OE]
thrittene [MI]
thirteen [ME]
þertien
https://www.etymonline.com/word/thirteen#etymonline_v_10762
https://www.merriam-webster.com/dictionary/thirteen
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED45531
https://bosworthtoller.com/32039