[nihzm]

Slavic languages in general seem to have retained this case and gender dependent declination of numbers, making them rather difficult to learn. For example most languages on this list [1] have complex declension tables for the number two.

https://en.wiktionary.org/wiki/%D0%B4%D0%B2%D0%B0

[ithkuil]

But it only works for numbers 1 and 2 and goes away for bigger numbers.

Probably a remnant of the dual case of Proto Indo European