Find All Factors of a Number using the Rainbow Method

There are a few ways how to find all the factors of a number. However, I think the easiest and the most intuitive way is by using the so-called rainbow method. Once you get the basic methodology of this technique, more likely, you will always remember it. Plus, the visual aspect of the rainbow method is very effective to keep track of all possible factors of a number.

The best way to learn this rainbow method in finding all the factors of a given number is to go over a few examples.

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Examples of Finding All Factors of a Number using the Rainbow Method

Example 1: Find all the factors of 18 using the Rainbow Method.

We’ll start by listing the first nine counting numbers.

Now, dividing 18 by the first number on the list, which is 1, we have 18 \div 1 = 18. Therefore, our first factor pair is 1 and 18.

We will write this first factor pair with enough space in between.

This time, let’s divide 18 by the second number on the list which is 2. Does it give us a factor pair? The answer is yes, because 18 \div 2 = 9. So our next factor pair is 2 and 9. Let’s write this factor pair on our rainbow diagram.

Moving on to the next number on the list, we ask ourselves again if 18 is divisible by 3. Sure it is! We have 18 \div 3 = 6.

So after 3, we test the next number which is 4. Is 18 divisible by 4? The answer is no. Therefore, we cannot write a factor pair with 4 as one of the factors. We are not done yet though because we have to go through all the numbers on the list until we hit a stopping point.

Since we cannot make a factor pair with 4, we move on to 5. Unfortunately, 18 is also not divisible by 5 so the next number to test is 6. But, notice that we already have a factor pair with 6 in our rainbow diagram. This is where we stop.

We can now list all the possible factors of 18:

Example 2: Find all the factors of the number 42 using the Rainbow Method.

Always have a list nearby of the counting numbers, at least from 1 to 9.

We should already know that any whole number is divisible by 1 which means our first factor pair will always be 1 and the given whole number. That is, 1 and 42. Hold this thought for a moment. Checking it with the next counting number in line, 42 is obviously divisible by 2. Here are our factor pairs so far in a rainbow diagram.

The next counting number to check is 3. Since 42 \div 3 = 14 that means our next factor pair 3 and 14. I will leave it to you to check that 4 and 5 do not evenly divide 42. This is our updated rainbow diagram of factor pairs.

Moving on, we know that 6 \times 7 = 42, therefore, we can include this factor pair in our diagram.

After 6, the next number to check is 7. However, 7 is already one of the factors as shown above so we stop here.

These are all the factors of the number 42:

Example 3: Find all the factors of the whole number 60 using the Rainbow Method.

This one is actually very easy. Keep in mind the first nine counting numbers. Let’s go through it together. We know that 1 evenly divides 60. How about 2 and 3? It is crystal clear that both 2 and 3 evenly divides 60. In addition, by doing a quick mental calculation, the next counting numbers which are 4, 5, and 6 can divide 60 without remainders. So for a recap, the counting numbers from 1 to 6 produce factor pairs. Again, I will leave it to you to verify that 60 is not divisible by 7, 8, or 9. You might say that 10 divides 60. But 10 is already covered by the factor pair 6 and 10. Below is the complete rainbow diagram of 60:

The following is a list of all the factors of 60: