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The common factors are 1 and 7. (7 = 1 x 7 and 21 = 3 x 7)

The only common prime factor is 7, which is also the largest common factor.

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Multiples of 21 include 21, 42, 63, 84 and so on. For them to be common, they need to be compared to another set of multiples.

You need at least two numbers to find a GCF.

Multiples of 21 include 21, 42, 63, 84 and 105. For them to be common, they need to be compared to another set of multiples.

Q: What are the common multiples of 21?

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The least common multiple of the numbers 72 and 21 is 504.

Multiples of 3 are 3, 6, 9 and so on. Multiples of 7 are 7, 14, 21 and so on. The common multiples of 3 and 7 include 21, 42, 63 and so on.

Multiply them together.

21, 42, 63 and so on.

There are 10 multiples of 6 in that range.

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LCM of 21 & 49 is 147, so all multiples of 147 are common multiples of 21 & 49.

there are infinite amount of common multiples.

The common multiples of 9 and 21 are 63, 126, 189 and so on.

Two common multiples of 21 and 15 are 105 and 315.

The common multiples of 3 and 21 are 21, 42, 63 and so on.

Multiply 21 and 11 to get a common multiple. Since 21 and 11 have no common factors, that also happens to be the least common multiple.All other common multiples are multiples of this least common multiple.

Any pair of numbers has an infinite set of common multiples. The lowest common multiple of 9 and 21 is 63 and the others are multiples of this, e.g. 63, 126, 189, 252, 315, ...

Odd multiples of 21.

Multiples of 21 include 21, 42, 63, 84 and so on. For them to be common, they need to be compared to another set of multiples.

Any multiple of 21.

105

Common multiples include 168, 336 and 504