Each letter can be 25 others.
A => B, C, D, E, F, G, ..............
B => A, C, D, E, F, G, ..............
etc.
Based on that, I think it would be like 2625 or something. It's probably more complicated than that, because once A has a value, B has one less value to choose from. So that would make it 26!....
Either way, it's an impossible number to bruteforce.