Q: What is the prime factorization of the number 21,021,211?

Why is the prime factorization of 21,021,211 written as 307¹ x 68,473¹?

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 21,021,211

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.

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

Let's start by dividing 21,021,211 by 2

21,021,211 ÷ 2 = 10,510,605.5 - This has a remainder. Let's try another prime number.
21,021,211 ÷ 3 = 7,007,070.3333 - This has a remainder. Let's try another prime number.
21,021,211 ÷ 5 = 4,204,242.2 - This has a remainder. Let's try another prime number.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
21,021,211 ÷ 307 = 68,473 - No remainder! 307 is one of the factors!
68,473 ÷ 307 = 223.0391 - There is a remainder. We can't divide by 307 evenly anymore. Let's try the next prime number
68,473 ÷ 311 = 220.1704 - This has a remainder. 311 is not a factor.
68,473 ÷ 313 = 218.7636 - This has a remainder. 313 is not a factor.
68,473 ÷ 317 = 216.0032 - This has a remainder. 317 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
68,473 ÷ 68,473 = 1 - No remainder! 68,473 is one of the factors!

The orange divisor(s) above are the prime factors of the number 21,021,211. If we put all of it together we have the factors 307 x 68,473 = 21,021,211. It can also be written in exponential form as 307¹ x 68,473¹.

Factor Tree

Another way to do prime factorization is to use a factor tree. Below is a factor tree for the number 21,021,211.

	21,021,211
307		68,473

More Prime Factorization Examples

Try the factor calculator