The prime number 73,939,133 has a very strange property.
If you keep removing a digit from the right hand end of the number, each of the remaining numbers is also prime.
It's the largest number known with this property.
Take a look: 73,939,133 and 73,939,13 and 73,939,1 and 73,939 and 7,393 and 739 and 73 and 7 are all prime!