I was especially impressed by the "Flash Anzan" (imaginary abacus) competition:
...[I]t requires contestants to use the mental image of an abacus. Since when you get very good at the abacus it is possible to calculate simply by imagining one. In Flash Anzan, 15 numbers are flashed consecutively on a giant screen. Each number is between 100 and 999. The challenge is to add them up. Simple, right? Except the numbers are flashed so fast you can barely read them.