Definition of a Prime Number

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A prime number is a positive whole number with exactly two factors, which are one and itself. Identify a variety of prime numbers, such as seven and 11, with help from a math teacher in this free video on math help and prime numbers.

Part of the Video Series: Algebra & Math Help
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What is the definition of a prime number? Hi, I'm Jimmy Chang. I've been teaching college mathematics for over nine years and a prime number by definition is a positive whole number with exactly two factors: one and itself. So in other words if a number is prime, if the only numbers that will go into it are one and the number itself. So here's a few examples as to what are prime numbers and what are not prime numbers. Now one number that comes to mind is the number 2. 2 is a prime number because the only factors of 2 are 1 and 2. You can also go down the list fairly quickly and see that 3, 5, 7 and 11 those are other examples of prime numbers because if you look at the factors very closely you'll see that the factors of those numbers are just 1 and themselves. They're still trying to find out the largest prime number out there and so prime numbers so far they do keep going. The number of prime numbers are still increasing as we speak. Now, there's some numbers are that are not prime for example are 4 and 8, 14 for example. Those are not prime numbers because the factors of these numbers are more than just 1 and itself. For example with 4 you know 2 goes into 4 so 4's not a prime number. With 8, factors of 8 are 1 and 8 but also 2 and 4. And with 14, you know that 2 and 7 go into 14 so those are numbers or examples of not prime numbers. These are examples of what's called composite numbers. Now the number 1 itself, it's not a prime number because the definition of a prime number you have to have two factors, 1 and itself. For the number 1 because it's just the number 1 that's only one factor. You need to have two factors. So the number 1 is not a prime number. So I'm Jimmy Chang and that gives you some demonstrations of the definition of a prime number.

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