freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-58-spiral-primes.english.md

---
id: 5900f3a61000cf542c50feb9
challengeType: 5
title: 'Problem 58: Spiral primes'
---

## Description
<section id='description'>
Starting with 1 and spiralling anticlockwise in the following way, a square spiral with side length 7 is formed.
37 36 35 34 33 32 31
38 17 16 15 14 13 30
39 18  5  4  3 12 29
40 19  6  1  2 11 28
41 20  7  8  9 10 27
42 21 22 23 24 25 2643 44 45 46 47 48 49
It is interesting to note that the odd squares lie along the bottom right diagonal, but what is more interesting is that 8 out of the 13 numbers lying along both diagonals are prime; that is, a ratio of 8/13 ≈ 62%.
If one complete new layer is wrapped around the spiral above, a square spiral with side length 9 will be formed. If this process is continued, what is the side length of the square spiral for which the ratio of primes along both diagonals first falls below 10%?
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler58()</code> should return 26241.
    testString: assert.strictEqual(euler58(), 26241, '<code>euler58()</code> should return 26241.');

```

</section>

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

<div id='js-seed'>

```js
function euler58() {
  // Good luck!
  return true;
}

euler58();
```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```
</section>