freeCodeCamp/curriculum/challenges/chinese/10-coding-interview-prep/project-euler/problem-216-investigating-the-primality-of-numbers-of-the-form-2n2-1.md

---
id: 5900f4451000cf542c50ff57
challengeType: 5
videoUrl: ''
title: 问题216：调查2n2-1形式的数字的素数
---

## Description
<section id="description">考虑形式为t（n）= 2n2-1的数字t（n），其中n&gt; 1.第一个这样的数字是7,17,31,49,71,97,127和161.事实证明只有49 = 7 * 7和161 = 7 * 23不是素数。对于n≤10000，有2202个数字t（n）是素数。 <p>对于n≤50,000,000，有多少个数t（n）是素数？ </p></section>

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

## Tests
<section id='tests'>

```yml
tests:
  - text: <code>euler216()</code>应该返回5437849。
    testString: assert.strictEqual(euler216(), 5437849);

```

</section>

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

<div id='js-seed'>

```js
function euler216() {
  // Good luck!
  return true;
}

euler216();

```

</div>



</section>

## Solution
<section id='solution'>

```js
// solution required
```

/section>