Q: What is the prime factorization of the number 802,170,725?

Why is the prime factorization of 802,170,725 written as 5² x 31² x 173¹ x 193¹?

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 802,170,725

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 802,170,725 by 2

802,170,725 ÷ 2 = 401,085,362.5 - This has a remainder. Let's try another prime number.
802,170,725 ÷ 3 = 267,390,241.6667 - This has a remainder. Let's try another prime number.
802,170,725 ÷ 5 = 160,434,145 - No remainder! 5 is one of the factors!
160,434,145 ÷ 5 = 32,086,829 - No remainder! 5 is one of the factors!
32,086,829 ÷ 5 = 6,417,365.8 - There is a remainder. We can't divide by 5 evenly anymore. Let's try the next prime number
32,086,829 ÷ 7 = 4,583,832.7143 - This has a remainder. 7 is not a factor.
32,086,829 ÷ 11 = 2,916,984.4545 - This has a remainder. 11 is not a factor.
32,086,829 ÷ 13 = 2,468,217.6154 - This has a remainder. 13 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
32,086,829 ÷ 31 = 1,035,059 - No remainder! 31 is one of the factors!
1,035,059 ÷ 31 = 33,389 - No remainder! 31 is one of the factors!
33,389 ÷ 31 = 1,077.0645 - There is a remainder. We can't divide by 31 evenly anymore. Let's try the next prime number
33,389 ÷ 37 = 902.4054 - This has a remainder. 37 is not a factor.
33,389 ÷ 41 = 814.3659 - This has a remainder. 41 is not a factor.
33,389 ÷ 43 = 776.4884 - This has a remainder. 43 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
33,389 ÷ 173 = 193 - No remainder! 173 is one of the factors!
193 ÷ 173 = 1.1156 - There is a remainder. We can't divide by 173 evenly anymore. Let's try the next prime number
193 ÷ 179 = 1.0782 - This has a remainder. 179 is not a factor.
193 ÷ 181 = 1.0663 - This has a remainder. 181 is not a factor.
193 ÷ 191 = 1.0105 - This has a remainder. 191 is not a factor.
193 ÷ 193 = 1 - No remainder! 193 is one of the factors!

The orange divisor(s) above are the prime factors of the number 802,170,725. If we put all of it together we have the factors 5 x 5 x 31 x 31 x 173 x 193 = 802,170,725. It can also be written in exponential form as 5² x 31² x 173¹ x 193¹.

Factor Tree

Another way to do prime factorization is to use a factor tree. Below is a factor tree for the number 802,170,725.

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