[math-fun] number of sodoku squares ?

Forgive me if I missed this in the previous sodoku discussion, but how many "essentially inequivalent" such (completely filled in) squares are there? By "essentially inequivalent", I mean modulo the following symmetries: 1. the group of rotations & flips of the entire square. 2. the symmetries of exchanging rows & columns. Exchanging entire 3x3 blocks gives 3!; exchanging rows & columns within blocks gives (3!)*(3!)*(3!). 3. relabelling of the integers from 1-9. So if "1" becomes "9" and "9" becomes "1", they are the "same" square. After all of these symmetries, I would imagine that there could only be a handful of inequivalent squares -- perhaps only one?