freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-401-sum-of-squares-of-divisors.english.md

---
id: 5900f4fd1000cf542c51000f
challengeType: 5
title: 'Problem 401: Sum of squares of divisors'
---

## Description
<section id='description'>
The divisors of 6 are 1,2,3 and 6.
The sum of the squares of these numbers is 1+4+9+36=50.


Let sigma2(n) represent the sum of the squares of the divisors of n.
Thus sigma2(6)=50.

Let SIGMA2 represent the summatory function of sigma2, that is SIGMA2(n)=∑sigma2(i) for i=1 to n.
The first 6 values of SIGMA2 are: 1,6,16,37,63 and 113.


Find SIGMA2(1015) modulo 109.
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler401()</code> should return 281632621.
    testString: assert.strictEqual(euler401(), 281632621, '<code>euler401()</code> should return 281632621.');

```

</section>

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

<div id='js-seed'>

```js
function euler401() {
  // Good luck!
  return true;
}

euler401();
```

</div>



</section>

## Solution
<section id='solution'>

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