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curriculum/challenges/english/10-coding-interview-prep/rosetta-code/factorial.md

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+---
+title: Factorial
+id: 597b2b2a2702b44414742771
+challengeType: 5
+forumTopicId: 302263
+---
+
+## Description
+<section id='description'>
+Write a function to return the factorial of a number.
+Factorial of a number is given by:
+<pre>
+<big>n! = n * (n-1) * (n-2) * ..... * 1</big>
+</pre>
+For example:
+<ul>
+  <li><code>3! = 3 * 2 * 1 = 6</code></li>
+  <li><code>4! = 4 * 3 * 2 * 1 = 24</code></li>
+</ul>
+<strong>Note:</strong> <code>0! = 1</code>
+</section>
+
+## Instructions
+<section id='instructions'>
+
+</section>
+
+## Tests
+<section id='tests'>
+
+```yml
+tests:
+  - text: <code>factorial</code> should be a function.
+    testString: assert(typeof factorial === 'function');
+  - text: <code>factorial(2)</code> should return a number.
+    testString: assert(typeof factorial(2) === 'number');
+  - text: <code>factorial(3)</code> should return 6.
+    testString: assert.equal(factorial(3), 6);
+  - text: <code>factorial(5)</code> should return 120.
+    testString: assert.equal(factorial(5), 120);
+  - text: <code>factorial(10)</code> should return 3,628,800.
+    testString: assert.equal(factorial(10), 3628800);
+
+```
+
+</section>
+
+## Challenge Seed
+<section id='challengeSeed'>
+
+<div id='js-seed'>
+
+```js
+function factorial(n) {
+
+}
+```
+
+</div>
+
+
+</section>
+
+## Solution
+<section id='solution'>
+
+
+```js
+function factorial(n) {
+  let sum = 1;
+  while (n > 1) {
+    sum *= n;
+    n--;
+  }
+  return sum;
+}
+
+
+```
+
+</section>