Khan Academy
Khan Academy: Prime Numbers
Discusses the properties of prime numbers and how to recognize them. [8:12] It includes a link to a practice exercise.
Khan Academy
Khan Academy: Prime Numbers
Prime numbers are numbers that have only 2 factors: 1 and themselves. For example, the first 5 prime numbers are 2, 3, 5, 7, and 11. By contrast, numbers with more than 2 factors are called composite numbers.