Q: What are the factor combinations of the number 21,120?

How do I find the factor combinations of the number 21,120?

Unfortunately, there's not simple formula to identifying all of the factors of a number and it can be a tedious process when trying to identify the divisors of larger numbers. To find the factor combinations of the number 21,120, it is easier to work with a table - it's called factoring from the outside in.

Outside in Factoring

We start by creating a table and writing 1 on the left side and then the number we're trying to find the factors for on the right side in a table. Then, below that, write the numbers as a negative as well.

1		21,120
-1		-21,120

With that explanation out of the way, let's continue. Next, we take the number 21,120 and divide it by 2:

21,120 ÷ 2 = 10,560

If the quotient is a whole number, then 2 and 10,560 are factors. In this case, the quotient is a whole number. Write them in the table inside the other two factors like the below example. Don't forget to write the negative numbers too!

Here is what our table should look like at this step:

Now, we try dividing 21,120 by 3:

21,120 ÷ 3 = 7,040

If the quotient is a whole number, then 3 and 7,040 are factors. In this case, the quotient is a whole number. Write them in the table inside the other two factors like the below example. Don't forget to write the negative numbers too!

Here is what our table should look like at this step:

Let's try dividing by 4:

21,120 ÷ 4 = 5,280

If the quotient is a whole number, then 4 and 5,280 are factors. In this case, the quotient is a whole number. Write them in the table inside the other two factors like the below example. Don't forget to write the negative numbers too!

Here is what our table should look like at this step:

If you did it right, you will end up with this table:

More Examples

Here are some more numbers to try:

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