---
id: 5900f4d01000cf542c50ffe2
challengeType: 5
title: 'Problem 355: Maximal coprime subset'
---
## 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).
## Instructions
## Tests
```yml
tests:
- text: euler355() should return 1726545007.
testString: assert.strictEqual(euler355(), 1726545007, 'euler355() should return 1726545007.');
```
## Challenge Seed
```js
function euler355() {
// Good luck!
return true;
}
euler355();
```