2, 3, 5, 7, 11, 13, 17, 19...

Prime-Numbers.net

Where Prime Numbers mysteries are solved.

Prime Numbers Practice

Here are links to the best math practice site I've found on the Web, IXL. They have a skill for everything you need to learn in K-12, and everything is aligned to the state and common core standards. Here are the skills pertaining to prime numbers:

IXL Math, the Web's #1 math practice site!

Also download IXL's free app!