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# Prime Factors
Compute the prime factors of a given natural number.
A prime number is only evenly divisible by itself and 1.
Note that 1 is not a prime number.
## Example
What are the prime factors of 60?
- Our first divisor is 2. 2 goes into 60, leaving 30.
- 2 goes into 30, leaving 15.
- 2 doesn't go cleanly into 15. So let's move on to our next divisor, 3.
- 3 goes cleanly into 15, leaving 5.
- 3 does not go cleanly into 5. The next possible factor is 4.
- 4 does not go cleanly into 5. The next possible factor is 5.
- 5 does go cleanly into 5.
- We're left only with 1, so now, we're done.
Our successful divisors in that computation represent the list of prime
factors of 60: 2, 2, 3, and 5.
You can check this yourself:
- 2 * 2 * 3 * 5
- = 4 * 15
- = 60
- Success!
## Running the tests
1. Go to the root of your PHP exercise directory, which is `<EXERCISM_WORKSPACE>/php`.
To find the Exercism workspace run
% exercism debug | grep Workspace
1. Get [PHPUnit] if you don't have it already.
% wget --no-check-certificate https://phar.phpunit.de/phpunit.phar
% chmod +x phpunit.phar
2. Execute the tests:
% ./phpunit.phar prime-factors/prime-factors_test.php
[PHPUnit]: http://phpunit.de
## Source
The Prime Factors Kata by Uncle Bob [http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata](http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata)
## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
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