Arthur Benjamin: Lightning calculation and other “Mathemagic”
In this video Arthur Benjamin calculates squares of 2, 3, and 4 digit numbers faster than you can do it on a calculator. I know. I tried to keep up while watching the video. Audience members give him their birth date and he tells them what day of the week they were born. Wait until you see what he does for his grand finale.
[Edit: Fixed YouTube link]