Q: What is the prime factorization of the number 21,061,280?

 A:
  • The prime factors are: 2 x 2 x 2 x 2 x 2 x 5 x 139 x 947
    • or also written as { 2, 2, 2, 2, 2, 5, 139, 947 }
  • Written in exponential form: 25 x 51 x 1391 x 9471

Why is the prime factorization of 21,061,280 written as 25 x 51 x 1391 x 9471?

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 21,061,280

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 21,061,280 by 2

21,061,280 ÷ 2 = 10,530,640 - No remainder! 2 is one of the factors!
10,530,640 ÷ 2 = 5,265,320 - No remainder! 2 is one of the factors!
5,265,320 ÷ 2 = 2,632,660 - No remainder! 2 is one of the factors!
2,632,660 ÷ 2 = 1,316,330 - No remainder! 2 is one of the factors!
1,316,330 ÷ 2 = 658,165 - No remainder! 2 is one of the factors!
658,165 ÷ 2 = 329,082.5 - There is a remainder. We can't divide by 2 evenly anymore. Let's try the next prime number
658,165 ÷ 3 = 219,388.3333 - This has a remainder. 3 is not a factor.
658,165 ÷ 5 = 131,633 - No remainder! 5 is one of the factors!
131,633 ÷ 5 = 26,326.6 - There is a remainder. We can't divide by 5 evenly anymore. Let's try the next prime number
131,633 ÷ 7 = 18,804.7143 - This has a remainder. 7 is not a factor.
131,633 ÷ 11 = 11,966.6364 - This has a remainder. 11 is not a factor.
131,633 ÷ 13 = 10,125.6154 - This has a remainder. 13 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
131,633 ÷ 139 = 947 - No remainder! 139 is one of the factors!
947 ÷ 139 = 6.8129 - There is a remainder. We can't divide by 139 evenly anymore. Let's try the next prime number
947 ÷ 149 = 6.3557 - This has a remainder. 149 is not a factor.
947 ÷ 151 = 6.2715 - This has a remainder. 151 is not a factor.
947 ÷ 157 = 6.0318 - This has a remainder. 157 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
947 ÷ 947 = 1 - No remainder! 947 is one of the factors!

The orange divisor(s) above are the prime factors of the number 21,061,280. If we put all of it together we have the factors 2 x 2 x 2 x 2 x 2 x 5 x 139 x 947 = 21,061,280. It can also be written in exponential form as 25 x 51 x 1391 x 9471.

Factor Tree

Another way to do prime factorization is to use a factor tree. Below is a factor tree for the number 21,061,280.

21,061,280
Factor Arrows
210,530,640
Factor Arrows
25,265,320
Factor Arrows
22,632,660
Factor Arrows
21,316,330
Factor Arrows
2658,165
Factor Arrows
5131,633
Factor Arrows
139947

More Prime Factorization Examples

21,061,27821,061,27921,061,28121,061,282
21 x 32 x 72 x 23,8791291 x 1131 x 6,427131 x 7,020,427121 x 111 x 957,3311

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