answersLogoWhite

0

21 has factors other than 1 and itself, so it is not a prime number. For example, it is divisible by 3. (You can check this by adding the digits of the number: 2 + 1 = 3. If the sum of the digits is divisible by 3, the number is also divisible by 3.) Therefore, 21 is a composite number.

User Avatar

Wiki User

15y ago

Still curious? Ask our experts.

Chat with our AI personalities

ReneRene
Change my mind. I dare you.
Chat with Rene
JudyJudy
Simplicity is my specialty.
Chat with Judy
SteveSteve
Knowledge is a journey, you know? We'll get there.
Chat with Steve

Add your answer:

Earn +20 pts
Q: Explain why 21 is not a prime number?
Write your answer...
Submit
Still have questions?
magnify glass
imp