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Oct07

# Prime Numbers: Do You Know What They Are?

There are some very special numbers you’ve probably heard of many times. They are called prime numbers. But, what are they? That is what we will talk about in today’s post. I hope that once you have read this post, you will know very well how to answer when someone asks … do you know what prime numbers are?

Let’s think first about a problem.

Sarah has 6 pieces of candy that she wants to share but does not know with how many people she can share so that everyone gets the same amount of pieces of candy and none are left. How many ways can she do so?

Here are Sarah and her 6 candies

How can we divide them?

The first and easiest is to give them all to one person, i.e. divide it by 1. That person would get 6 pieces of candy!

The next possibility is to divide it among 2 people. And since 6 divided by 2 is 3, each person would get 3 pieces of candy!

Let’s go to the next number, 3. If we divide 6 pieces of candy between 3 people, we also have an exact division and give 2 pieces of candy to each person:

We continue with the numbers. We do not have exact divisions for 4 or 5, but we do have a division of 6. As 6 divided by 6 is 1, we can give one piece of candy to each of the 6 children.

Let’s collect all our information. We know that 6 pieces of candy can be distributed (being an exact distribution) between 1, 2, 3 and 6 people. That is, the number 6 can be divided, so that the remainder is 0, between 1, 2, 3 and 6. These numbers are called divisors of 6.

Let’s try with another number. For example 7. Now Sarah has 7 candies

As before, you can divide it by 1 and give all the candy to one person:

How lucky Mark is to be given all of the candy!

Are there any other ways to do it? We cannot divide 7 by 2 or by 3 or by 4, or by 5 or by 6 … so we only have 7! Sarah can distribute the candy among 7 people giving one piece to each.

So 7 can only be divided by 1 and 7.  Its only divisors are 1 and 7. These type of numbers are what we call prime numbers.

Are there more prime numbers? Of course! Let’s search for some more:

• 4? No! Because its divisors are 1, 2 and 4.
• 5? Yes! Because its divisors are 1 and 5.
• 8? No! Because its divisors are 1, 2, 4 and 8.

In summary, a number is prime if it only has two divisors: 1 and itself.

Now you can find a lot of prime numbers!

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