freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/project-euler/problem-258-a-lagged-fibonacci-sequence.english.md

---
id: 5900f46e1000cf542c50ff81
challengeType: 5
title: 'Problem 258: A lagged Fibonacci sequence'
---

## Description
<section id='description'>
A sequence is defined as:

gk = 1, for 0 ≤ k ≤ 1999
gk = gk-2000 + gk-1999, for k ≥ 2000.
Find gk mod 20092010 for k = 1018.
</section>

## Instructions
<section id='instructions'>

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler258()</code> should return 12747994.
    testString: assert.strictEqual(euler258(), 12747994, '<code>euler258()</code> should return 12747994.');

```

</section>

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

<div id='js-seed'>

```js
function euler258() {
  // Good luck!
  return true;
}

euler258();
```

</div>



</section>

## Solution
<section id='solution'>

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