Definition
Composite number
A composite number is a whole number greater than 1 with more than two positive factors.
What it means
A composite number can be built as a non-trivial rectangle. Besides a row of 1 and the whole number, it has another factor pair. That extra factor pair is what makes the number composite.
Remember it
Composite numbers can make an extra rectangle, not only 1 by the number.
Example
Twenty-one is composite because 21 = 3 × 7. Its positive factors are 1, 3, 7, and 21, so it has more than two positive factors.
Watch for
The number 1 is neither prime nor composite because it has only one positive factor. Zero is not classified as prime or composite.
Common mix-up
Composite does not mean even. For example, 21 is odd and composite, while 2 is even and prime.
Exact meaning
A composite number is a whole number greater than 1 that has more than two positive factors. Equivalently, it can be written as a product of two whole numbers that are both greater than 1.