Help with a riddle please

[MooMoo_Cowfreak]

So I'm playing Neverwinter Nights 2, and there's this riddle. It's answer should be a three digit number, but I can't seem to find it. (I have tried gamefaqs but the puzzle is randomized so there is no definite answer,)

9 are we when taken all 3.

Last one slain than six remain.

None survive, our first less five.

I've tried but I can't seem to find it.

Thanks!