Back from AFA land. Also, sudoku

[igotrhythm]

*Away From Arrows

One of my many distractions away from keysmashing (I feel like I've dropped to D4, lul) was sudoku. I found some of my old books, and I remember thinking, how many ways can you fill in a grid while adhering to the rules? This is strictly solved grids, as you can leave any number of clues to make it more complicated.

And that was when I hit on the idea of congruent sudoku. That is, if you replace the numbers with colors, then reassign numbers to get a second sudoku, then the two grids are congruent. Alternately, you can get to one from the other by swapping the positions of numbers within the row/column/box.

So that makes me wonder...how many solution grids are out there, assuming a standard 9x9 grid?

[rushyrulz]

5,472,730,538