freeCodeCamp/curriculum/challenges/english/10-coding-interview-prep/project-euler/problem-443-gcd-sequence.english.md

---
id: 5900f5271000cf542c51003a
challengeType: 5
isHidden: false
title: 'Problem 443: GCD sequence'
forumTopicId: 302115
---

## Description
<section id='description'>

Let g(n) be a sequence defined as follows:
g(4) = 13,
g(n) = g(n-1) + gcd(n, g(n-1)) for n > 4.

The first few values are:

n 4567891011121314151617181920...
g(n) 1314161718272829303132333451545560...
<!-- TODO Use MathJax -->

You are given that g(1 000) = 2524 and g(1 000 000) = 2624152.

Find g(1015).
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler443()</code> should return 2744233049300770.
    testString: assert.strictEqual(euler443(), 2744233049300770);

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='js-seed'>

```js
function euler443() {
  // Good luck!
  return true;
}

euler443();
```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```

</section>