I'm going to have another crack at this tonight....thought I was doing ok but like ortolan @ post 29, I got stuck with finding n and p to fit with my s and t.
if you are still around crosswhit can you clarify the second sentence in post 31? That would help me! My s and t are two of the lowest 9 digit roman primes - is that right? Including the very lowest.
Also did we establish that 2 (ie II) is not a two digit roman prime? I think actually it is, but am going with the other two options for the puzzle.....