Before I was a memory champion, I was hugely into mental calculation. I wasn't any good, but I was interested in how the top mental calculators did it. One of the top guys is Rüdiger Gamm. He's known for taking a 2 digit number and raising it to a power (ex: 34^3 means 34x34x34 - basically being able to multiply a number by itself n times). It's actually really hard because the numbers get HUGE really quick. For a long time I always thought he just memorized it all, and even though a big part of it IS memorization, there is still some calculation involved. Either way, it's super impressive.
I got a chance to chat with him over Skype. Here's the interview!