What popped out immediately when learning the Finnish numbers was how long the words are. All of the other languages count with one or two syllable words. When pronounced, the Finnish is, minimum, two syllables. Three, seven and ten are three syllables. Eight and nine are four:
yksi
kaksi
kolme
neljä
viisi
kuusi
seitsemän
kahdeksan
yhdeksän
kymmenen
Twenty-First is: kahdeskymmenesensimmäinen
I've always wondered what it was about the history of the language and culture that led to this. Finnish does quite a bit of concatenating words to create other words. It was originally the same for numbers. For example, the longest, eight: kahdeksan was originally, literally, 'with two ten'. You can see hints of this in that kaksi (two) contains 'ka' and 'dek' references a borrowed word 'deca', ten.
Ref. http://goo.gl/Zt2WBb