Q: What is the prime factorization of the number 391,668?

 A:
  • The prime factors are: 2 x 2 x 3 x 127 x 257
    • or also written as { 2, 2, 3, 127, 257 }
  • Written in exponential form: 22 x 31 x 1271 x 2571

Why is the prime factorization of 391,668 written as 22 x 31 x 1271 x 2571?

What is prime factorization?

Prime factorization or prime factor decomposition is the process of finding which prime numbers can be multiplied together to make the original number.

Finding the prime factors of 391,668

To find the prime factors, you start by dividing the number by the first prime number, which is 2. If there is not a remainder, meaning you can divide evenly, then 2 is a factor of the number. Continue dividing by 2 until you cannot divide evenly anymore. Write down how many 2's you were able to divide by evenly. Now try dividing by the next prime factor, which is 3. The goal is to get to a quotient of 1.

If it doesn't make sense yet, let's try it...

Here are the first several prime factors: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29...

Let's start by dividing 391,668 by 2

391,668 ÷ 2 = 195,834 - No remainder! 2 is one of the factors!
195,834 ÷ 2 = 97,917 - No remainder! 2 is one of the factors!
97,917 ÷ 2 = 48,958.5 - There is a remainder. We can't divide by 2 evenly anymore. Let's try the next prime number
97,917 ÷ 3 = 32,639 - No remainder! 3 is one of the factors!
32,639 ÷ 3 = 10,879.6667 - There is a remainder. We can't divide by 3 evenly anymore. Let's try the next prime number
32,639 ÷ 5 = 6,527.8 - This has a remainder. 5 is not a factor.
32,639 ÷ 7 = 4,662.7143 - This has a remainder. 7 is not a factor.
32,639 ÷ 11 = 2,967.1818 - This has a remainder. 11 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
32,639 ÷ 127 = 257 - No remainder! 127 is one of the factors!
257 ÷ 127 = 2.0236 - There is a remainder. We can't divide by 127 evenly anymore. Let's try the next prime number
257 ÷ 131 = 1.9618 - This has a remainder. 131 is not a factor.
257 ÷ 137 = 1.8759 - This has a remainder. 137 is not a factor.
257 ÷ 139 = 1.8489 - This has a remainder. 139 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
257 ÷ 257 = 1 - No remainder! 257 is one of the factors!

The orange divisor(s) above are the prime factors of the number 391,668. If we put all of it together we have the factors 2 x 2 x 3 x 127 x 257 = 391,668. It can also be written in exponential form as 22 x 31 x 1271 x 2571.

Factor Tree

Another way to do prime factorization is to use a factor tree. Below is a factor tree for the number 391,668.

391,668
Factor Arrows
2195,834
Factor Arrows
297,917
Factor Arrows
332,639
Factor Arrows
127257

More Prime Factorization Examples

391,666391,667391,669391,670
21 x 111 x 191 x 9371231 x 17,02913591 x 1,091121 x 51 x 531 x 7391

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