---
title: Fibonacci sequence
id: 597f24c1dda4e70f53c79c81
localeTitle: 597f24c1dda4e70f53c79c81
challengeType: 5
---

## Description
<section id='description'> 
<p> Escribe una función para generar el <big>n <sup>º</sup></big> número de Fibonacci. </p> 
/// <p> El <big><sup>número</sup> n de</big> Fibonacci viene dado por: 
/// <p> F <sub>n</sub> = F <sub>n-1</sub> + F <sub>n-2</sub> </p> 
/// <p> Los dos primeros términos de la serie son 0, 1. </p> 
/// <p> Por lo tanto, la serie es: 0, 1, 1, 2, 3, 5, 8, 13 ... </p> 
/// 
</section>

## Instructions
<section id='instructions'> 

</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>fibonacci</code> es una función.
    testString: 'assert(typeof fibonacci === "function", "<code>fibonacci</code> is a function.");'
  - text: <code>fibonacci(2)</code> debe devolver un número.
    testString: 'assert(typeof fibonacci(2) == "number", "<code>fibonacci(2)</code> should return a number.");'
  - text: <code>fibonacci(3)</code> debe devolver 1. &quot;)
    testString: 'assert.equal(fibonacci(3),1,"<code>fibonacci(3)</code> should return 1.");'
  - text: <code>fibonacci(5)</code> debe devolver 3. &quot;)
    testString: 'assert.equal(fibonacci(5),3,"<code>fibonacci(5)</code> should return 3.");'
  - text: <code>fibonacci(10)</code> debe devolver 34. &quot;)
    testString: 'assert.equal(fibonacci(10),34,"<code>fibonacci(10)</code> should return 34.");'

```

</section>

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

<div id='js-seed'>

```js
function fibonacci(n) {
  // Good luck!
}
```

</div>



</section>

## Solution
<section id='solution'>


```js
function fibonacci(n) {
  let a = 0, b = 1, t;
  while (--n > 0) {
    t = a;
    a = b;
    b += t;
  }
  return a;
}

```

</section>