One, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve... they're unique names. Then comes thirten, fourten.
Ten, eleven and twelve are unique names and probably have their entymology derived from a base-12 numbering system once primarily used in Anglo-speaking countries.
It's simple enough to Google "etymology eleven" to see that it is a base 10 word.
Modern proponents of a dozenal system seem to prefer the words "el" and "doz" for eleven and twelve. I would totally be in for changing, but realistically it'll never happen.
Ten, eleven and twelve are unique names and probably have their entymology derived from a base-12 numbering system once primarily used in Anglo-speaking countries.