- Ask the willing participant to think of a three-digit number, and to commit it to memory or write it down so that you can't see it.
- Ask your friend to key in the digits of the number, and then key them in again, forming a six-digit number. For example, if the first number was 283, the number keyed in should be 283283.
- Ask your friend to divide the number in the previous step by 13. Surprisingly, the result is an integer.
- Now ask your friend to divide the number in the previous step by 11. Again, the result is an integer.
- Finally, ask your friend to divide the number in the previous step by 7.
- Tell your friend that this is the same number he/she started with.

Can someone come up with an explanation of how this works?