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189 is a composite. Some quick tests, which can be done in your head:

Check if the number is even (2 is a factor). Ones place will have 0,2,4,6, or 8 if even.

Multiple of 5 (5 is a factor): Ones digit is 0 or 5.

Multiple of 3 or 9: Add up the digits in the number; if this sum is 3 or a multiple of 3, then the original number is a multiple of 3 (3 is a factor). Additionally, if this sum equals 9 or a multiple of 9, then 9 is a factor. This is the case for 189 : 1+8+9=18, which is a multiple of 9.

Since we found a factor (in addition to 1 & the original number) then the number is composite and not prime.

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14y ago

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