Composite number
- CBSE · NCERT Class 6, Ch 5 Prime Time
A composite number is a whole number above 1 with more than two factors, such as 12, which is 3 × 4.
A composite number can be made by multiplying two smaller numbers, neither of them 1. 12 is composite, because 3 × 4 = 12. 13 is not, because only 1 × 13 makes it. Numbers like 13 are prime numbers.
Every number above 1 is either prime or composite. The number 1 is neither. It has just one factor, so it fits neither rule.
A small example
Is 51 composite? It looks prime at first. But its digits add to 5 + 1 = 6, which is a multiple of 3. So 3 divides 51, and 51 = 3 × 17. It has the factors 1, 3, 17 and 51. That is more than two, so 51 is composite.
To show a number is composite, one factor pair other than 1 and itself is enough. You do not need to list every factor.
Why it matters later
The fundamental theorem of arithmetic in Class 10 Chapter 1 is a statement about composite numbers. An exercise in that chapter asks why 7 × 11 × 13 + 13 is composite. The answer is the same idea as above. Take out 13 as a common factor, and the number has a factor pair other than 1 and itself.
Sources
Facts last checked against these sources on 30 September 2026.
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