"Oibríonn seachtar rúnaithe leis an mbreitheamh."

Translation: Seven secretaries work with the judge.

[scilling]

Wouldn’t the singular form of the noun be used with this number, viz seachtar rúnaí rather than seachtar rúnaithe?

[FearMhaighEo]

The numbers for counting people (beirt go deichniúr) are all nouns. They take the Ginideach Iolra after them. Beirt is also feminine so you add a seimhiú onto the next noun. You'll need to know the tréaniolra and lagiolra for these.

1. Duine amháin.

2. Beirt- Beirt fhear, Beirt mhúinteoirí.

3. Triúr- Triúr fear, Triúr múinteoirí.

4. Ceathrar- Ceathrar fear, Ceathrar múinteoirí.

The joys of the Tuiseal Ginideach, Hollywood will have to make a horror film out of it.

[galaxyrocker]

It actually looks like it gets put into the genitive plural. Which is why you have tríúr ban.

[scilling]

Ah, that makes sense, thank you. My Irish grammar book stated that the singular form of the noun should be used, but listed ban as an exception; it would have been clearer if it had stated that the genitive plural form should be used.

[galaxyrocker]

Note, I'm not 100% sure, but that's what it looks like (note: triúr fear, where fear is genitive plural of, well, fear). It's the only thing I can think of to make sense.

[dubhais]

As stated above, the genitive plural is traditionally used but that the nominative singular can be used with exceptions.

See here: http://www.nualeargais.ie/gnag/zahl4.htm#pears

Addendum: from p168 of the standard (available here: http://www.oireachtas.ie/parliament/media/Final-Version.pdf) is é an ginideach iolra den ainmfhocal a leanann an uimhir phearsanta. So, genitive plurals only in the course, please, but who knows what you may encounter in the wild.