DIV004 · Factors, multiples & divisibility · Classes 5–8
Composite numbers
A composite number has more than two factors, so it can be made as a rectangle in more than one way. 1 is neither prime nor composite.
15 = 3 × 5Composite numbers
📐 Formula
n is composite ⇔ n has a factor other than 1 and n
✏️ Worked example
15 has factors 1, 3, 5, 15, so it is composite.
🌍 Where it is used
Breaking numbers into factors to simplify fractions.
❓ Quick check
Which number is composite?
🏋️ Practice
EasyIs 9 prime or composite?
Answer: Composite (3 × 3)
MediumWhat is the smallest composite number?
Answer: 4
ChallengeList the composite numbers between 20 and 30.
Answer: 21, 22, 24, 25, 26, 27, 28