![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/step1.JPG\")
A prime number has exactly two whole number factors, 1 and itself.
\A composite number has more than two whole number factors.
\Express the number 21 as a product of its factors.
\Write the factors of 21. \ \
\21 = 1 × 21.
\21 = 3 × 7.
\Factors of 21 are 1, 3, 7 and 21.
\Since 21 has more than two factors, it is composite.![\"\"](\"http://www.mathskey.com/userfiles/image/steps_images/solution.JPG\")
The number 21 is a composite number.