So what are some ways to determine a prime number? Hi, I'm Jimmy Chang, and I've been teaching college mathematics for over nine years, and the first thing to determine if it's...a number is prime is to go over the definition of what a prime number is. Now, a prime number is a positive whole number with exactly two factors: one and itself. So basically, we're talking about any positive whole number that the...that the only numbers that will go into are going to be one and the number that's given. So basically, to determine if a number is prime, you can analyze it, think about your multiplication tables, or you can use factor trees. It's really, you know, up to you. But basically, some numbers that come to mind that are prime are, for example, two, three, five, seven, eleven -- the list can go on and on because, as we speak, they're still trying to find the next larger prime number. Now, if a number has factors other than one and itself, it's called a composite number. Now, those numbers obviously are not prime. For example, the number four is not prime because the factors of four besides one and four are two. Two goes into four. Also, 12 -- besides one and 12, you have two, six, three and four. Now, the one number that folks sometimes mistake for a prime number is the number one. Now, one is actually not a prime number because if you go back to the definition, to be a prime number, you have to have two factors: the number one and something else. Because the factors of one, really, is just one, it's only one factor. It's not two. So the number one is not prime. So I'm Jimmy Chang and that's how you determine a prime number.
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