256^3=16.7 million. Where does the 65,536 come from?

Thanks for all the help everyone. I made a living teaching college level mathematics, so you'd think I'd be able to figure this all out...

...but it is a struggle. Every subject area has its arcane language that is problematic for me! When I get my ink I'm just going to start experimenting and see what works, based on what I've done using Epson ABW and some ideas I've gotten from this thread. But I'd like to develop some understanding in parallel with that.