Q: What is the prime factorization of the number 81,405,641?

 A:
  • The prime factors are: 389 x 209,269
    • or also written as { 389, 209,269 }
  • Written in exponential form: 3891 x 209,2691

Why is the prime factorization of 81,405,641 written as 3891 x 209,2691?

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 81,405,641

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 81,405,641 by 2

81,405,641 ÷ 2 = 40,702,820.5 - This has a remainder. Let's try another prime number.
81,405,641 ÷ 3 = 27,135,213.6667 - This has a remainder. Let's try another prime number.
81,405,641 ÷ 5 = 16,281,128.2 - This has a remainder. Let's try another prime number.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
81,405,641 ÷ 389 = 209,269 - No remainder! 389 is one of the factors!
209,269 ÷ 389 = 537.9666 - There is a remainder. We can't divide by 389 evenly anymore. Let's try the next prime number
209,269 ÷ 397 = 527.1259 - This has a remainder. 397 is not a factor.
209,269 ÷ 401 = 521.8678 - This has a remainder. 401 is not a factor.
209,269 ÷ 409 = 511.6601 - This has a remainder. 409 is not a factor.
...
Keep trying increasingly larger numbers until you find one that divides evenly.
...
209,269 ÷ 209,269 = 1 - No remainder! 209,269 is one of the factors!

The orange divisor(s) above are the prime factors of the number 81,405,641. If we put all of it together we have the factors 389 x 209,269 = 81,405,641. It can also be written in exponential form as 3891 x 209,2691.

Factor Tree

Another way to do prime factorization is to use a factor tree. Below is a factor tree for the number 81,405,641.

81,405,641
Factor Arrows
389209,269

More Prime Factorization Examples

81,405,63981,405,64081,405,64281,405,643
32 x 71 x 171 x 291 x 2,621123 x 51 x 2,035,141121 x 31 x 13,567,6071111 x 1,2131 x 6,1011

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