21 is a composite number because it has factors other than 1 and itself. Its factors are 1, 3, 7, and 21. Since it can be divided by 3 and 7, it is not a prime number.
is 21 a prime or composite number
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1 answer
21 is a composite number because it has factors other than 1 and itself. Its factors are 1, 3, 7, and 21. Since it can be divided by 3 and 7, it is not a prime number.