We can't divide that 15 by 2, but we can divide it by 3 because 15 = 3 × 5, and 3 and 5 are both prime numbers. Since 60 is also divisible by 2, we "pull out" 2 from 60: That's always our "prime suspect." Oh, sure, groan away. Okay, 120 is divisible by 2, so first we "pull out" a 2:Īlways look first to see if you can pull out a 2. We'll illustrate what this means by an example, mostly because we're terrible at drawing stuff.
To find the prime factorization of a number, you can "pull out" one prime at a time. We have to use two copies of 2 and one copy of 3. We can reorder the product and write 12 = 2 × 3 × 2, or 12 = 3 × 2 × 2, but we can't write 12 as a product using any other prime numbers. By the way, how do you get invited to such cool parties?Įvery single whole number can be written uniquely (in only one way) as a product of primes. Having the ability to rattle them off will be a great party trick, if nothing else. However, if you want to memorize all 1000 of them, we won't stop you. It's good to be able to recognize the prime numbers at least up to 31 or so. For any other even number n, 2 divides into n, so n is not prime.Ĭlick here to see a list of the first 1000 primes. It's like someone fed it into a factor compactor.Ĥ is not prime because it's divisible by 2.Ħ is not prime because it's divisible by 2 and 3.Īs it turns out, 2 is the only even number that's prime. A prime number is a number greater than 1 that's only divisible by itself and 1.
0 kommentar(er)
