* When we multiply three numbers, we will get the prime numbers.
* The difference between the second and the first number is equal to the third and second.
There’s a girl who has a large family. She has an equal amount of brothers and sisters, but each brother only has half as many brothers and sisters. What’s the correct amount of brothers and sisters?
How many points are there on the globe where, by walking one mile south, then one mile east and then one mile north, you would reach the place where you started?
In 2007, a puzzle was released and $2 million prizes were offered for the first complete solution. The competition ended at noon on 31 December 2010, with no solution being found. Wiki