I think they are types of ordinal numbers used for dates....
But just as tricky as some of our ordninal numbers... "first, second, third, fourth... easy to learn then on for the non-English speaker until they reach 21 with no apparent reason why it has an "st" on the end rather than a "th"!!!
and then we start talking about pairs, couples, brace, gross... drives my Japanese friends nuts!.. but I think this is the same in just about every language...
and juyokka (14)
cheers