freeCodeCamp/curriculum/challenges/chinese/10-coding-interview-prep/project-euler/problem-25-1000-digit-fibonacci-number.md

---
id: 5900f3851000cf542c50fe98
challengeType: 5
videoUrl: ''
localeTitle: 问题25：1000位斐波纳契数
---

## Description
<section id="description"> Fibonacci序列由递归关系定义： <div style="padding-left: 4em;"> F <sub>n</sub> = F <sub>n-1</sub> + F <sub>n-2</sub> ，其中F <sub>1</sub> = 1且F <sub>2</sub> = 1。 </div>因此，前12个学期将是： <div style="padding-left: 4em; display: inline-grid; grid-template-rows: auto; row-gap: 7px;"><div> F <sub>1</sub> = 1 </div><div> F <sub>2</sub> = 1 </div><div> F <sub>3</sub> = 2 </div><div> F <sub>4</sub> = 3 </div><div> F <sub>5</sub> = 5 </div><div> F <sub>6</sub> = 8 </div><div> F <sub>7</sub> = 13 </div><div> F <sub>8</sub> = 21 </div><div> F <sub>9</sub> = 34 </div><div> F <sub>10</sub> = 55 </div><div> F <sub>11</sub> = 89 </div><div> F <sub>12</sub> = 144 </div></div>第12个学期F <sub>12</sub>是第一个包含三位数的术语。 Fibonacci序列中包含<var>n个</var>数字的第一项的索引是多少？ </section>

## Instructions
<section id="instructions">
</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>digitFibonacci(5)</code>应该返回21。
    testString: assert.strictEqual(digitFibonacci(5), 21);
  - text: <code>digitFibonacci(10)</code>应该返回45。
    testString: assert.strictEqual(digitFibonacci(10), 45);
  - text: <code>digitFibonacci(15)</code>应该返回69。
    testString: assert.strictEqual(digitFibonacci(15), 69);
  - text: <code>digitFibonacci(20)</code>应该返回93。
    testString: assert.strictEqual(digitFibonacci(20), 93);

```

</section>

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

<div id='js-seed'>

```js
function digitFibonacci(n) {
  // Good luck!
  return n;
}

digitFibonacci(20);

```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```

/section>