No, I'm not trying to create them. I'm just curious as to how many possible combinations there are, and how many numbers one needs to be unique. I started trying to compute the first one, and got through the first few squares, but once you try finding the combinations for the middle squares it gets tricky.

For example, for the upper leftmost square, there are 9 (1-9) different numbers you can put there. Then for the square to its right there are 8 possible numbers, since you can't use the first number again. You can go on down the line to find that there are 9! ways to fill the first row. Then, for the second row there are 6 ways to fill the first square, since it shares a 3X3 box with the three numbers above it, and you can't use any of those. So now you have 9!*6 ways to fill 1 row and 1 square in the next row. And so on...