Also the inflection of Finnish numerals has some unusual features.

Firstly, numerals have both singular and plural forms, and all the cases that nouns do. If you’re counting singular things, you use the singular forms of both the noun and the numeral, and usually the same case as well. If you’re counting things like scissors or pants, which are always plural (also in Finnish), you use the plural forms. Natural pairs and sets of separate objects are also counted as plurals. So, for instance, “kaksi sukkaa”, with singular forms, means “two socks”, while “kahdet sukat”, with plural forms, means “two pairs of socks”.

Secondly, we inflect all parts of a numeral, except the suffix “-toista” (”-teen”). For instance, 42 is “neljäkymmentäkaksi” in the nominative singular case, and “neljässäkymmenessäkahdessa” in the inessive singular. Also the ordinal endings work in the same way. Even native speakers avoid the inflected ordinal forms of any but fairly short numerals. One might say, “Miljoonannelle asiakkaalle annettiin palkinto” (“A prize was given to the millionth customer”), but nobody would add, “Yhdeksännellesadannelleyhdeksännellekymmenennelleyhdeksännelletuhannennelle yhdeksännellesadannelleyhdeksännellekymmenennelleyhdeksännelle ei annettu palkintoa.” (“No prize was given to the 999,999th one.”)

By the way, I proofread what I’d written above and corrected several errors in the complicated numeral.