Im not sure what this is called, which is why im having trouble searching for it.

What im looking to do, is take numbers, and convert them to some alpha numeric base so that the number say 5000, wouldnt read 5000, but like G4u or something like that. The idea being to save space and also not make it obvious how many records there are in a given system. Im using php, so if there is something like this built into php even better, but even a name for this method would be helpful at this point

Again, sorry for not being able to be more clear, im just not sure what this is called.