Prime95 is a tool especially designed to work with prime numbers. This is a tool perfect for elementary and high school students. This application will find for you the Mersennes's prime numbers and help you perform mathematical equations with them.
The great thing about this software is that it uses a central server that gives you correct answers in a full explained report in a matter of minutes; all you need to use it is an Internet connection.
It's interface is user friendly, very Windows-like and it will take you only a few minutes to understand how to use it.