Prime Number Definition: a plain-English explanation of what the term means, why it matters in math, and how it is used, followed by worked examples and practice questions so the definition turns into something you can apply.
A prime number has exactly two factors: 1 and itself. That definition is why 1 is not prime, and why 2 is the only even prime number.
Math Dictionary / Prime Number
Prime Number
A prime number is a whole number greater than 1 with exactly two factors: 1 and itself.
Number SystemGrade 4Grade 5Grade 6GED
What it means
Prime numbers cannot be divided evenly by other whole numbers.
Also called: prime
Examples
| 2 is prime |
| 7 is prime |
| 9 is not prime because 3 x 3 = 9 |
Common mistake
The number 1 is not prime because it has only one factor.
Try one
Question: Is 11 prime?
Show answer
Yes. Its only factors are 1 and 11.