---
id: 5900f5261000cf542c510038
challengeType: 5
title: 'Problem 441: The inverse summation of coprime couples'
---
## Description
For an integer M, we define R(M) as the sum of 1/(p·q) for all the integer pairs p and q which satisfy all of these conditions:
1 ≤ p < q ≤ M
p + q ≥ M
p and q are coprime.
We also define S(N) as the sum of R(i) for 2 ≤ i ≤ N.
We can verify that S(2) = R(2) = 1/2, S(10) ≈ 6.9147 and S(100) ≈ 58.2962.
Find S(107). Give your answer rounded to four decimal places.
## Instructions
## Tests
```yml
tests:
- text: euler441() should return 5000088.8395.
testString: assert.strictEqual(euler441(), 5000088.8395, 'euler441() should return 5000088.8395.');
```
## Challenge Seed
```js
function euler441() {
// Good luck!
return true;
}
euler441();
```