---
id: 5900f4d01000cf542c50ffe2
challengeType: 5
title: 'Problem 355: Maximal coprime subset'
forumTopicId: 302015
---

## Description
<section id='description'>
Define Co(n) to be the maximal possible sum of a set of mutually co-prime elements from {1, 2, ..., n}. For example Co(10) is 30 and hits that maximum on the subset {1, 5, 7, 8, 9}.



You are given that Co(30) = 193 and Co(100) = 1356.


Find Co(200000).
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler355()</code> should return 1726545007.
    testString: assert.strictEqual(euler355(), 1726545007);

```

</section>

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

<div id='js-seed'>

```js
function euler355() {
  // Good luck!
  return true;
}

euler355();
```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```

</section>