Q: What is the prime factorization of the number 21,412,661?

Why is the prime factorization of 21,412,661 written as 31¹ x 311¹ x 2,221¹?

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 21,412,661

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 21,412,661 by 2

21,412,661 ÷ 2 = 10,706,330.5 - This has a remainder. Let's try another prime number.
21,412,661 ÷ 3 = 7,137,553.6667 - This has a remainder. Let's try another prime number.
21,412,661 ÷ 5 = 4,282,532.2 - This has a remainder. Let's try another prime number.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
21,412,661 ÷ 31 = 690,731 - No remainder! 31 is one of the factors!
690,731 ÷ 31 = 22,281.6452 - There is a remainder. We can't divide by 31 evenly anymore. Let's try the next prime number
690,731 ÷ 37 = 18,668.4054 - This has a remainder. 37 is not a factor.
690,731 ÷ 41 = 16,847.0976 - This has a remainder. 41 is not a factor.
690,731 ÷ 43 = 16,063.5116 - This has a remainder. 43 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
690,731 ÷ 311 = 2,221 - No remainder! 311 is one of the factors!
2,221 ÷ 311 = 7.1415 - There is a remainder. We can't divide by 311 evenly anymore. Let's try the next prime number
2,221 ÷ 313 = 7.0958 - This has a remainder. 313 is not a factor.
2,221 ÷ 317 = 7.0063 - This has a remainder. 317 is not a factor.
2,221 ÷ 331 = 6.71 - This has a remainder. 331 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
2,221 ÷ 2,221 = 1 - No remainder! 2,221 is one of the factors!

The orange divisor(s) above are the prime factors of the number 21,412,661. If we put all of it together we have the factors 31 x 311 x 2,221 = 21,412,661. It can also be written in exponential form as 31¹ x 311¹ x 2,221¹.

Factor Tree

Another way to do prime factorization is to use a factor tree. Below is a factor tree for the number 21,412,661.

	21,412,661
31		690,731
	311		2,221

More Prime Factorization Examples

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