[dctaflin]

Fascinating. I studied Finnish for three years and it never occurred to me that the numbers 8 and 9 (kahdeksan and yhdeksan) mean 2-from-10 and 1-from-10. Though 10 isn't "deksan", it's "kymmenen". Still the "yh" and "kah" should have been clearly seen as akin to "yksi" and "kaksi" (one and two).

[Ekaros]

I think modern theory is that stem is something like "-eksa" meaning without. And link to indoeuropean ten is just coincidence. Likely more believable to me looking at rest of the small numbers, which are pretty local.