---
id: 5900f4311000cf542c50ff44
challengeType: 5
title: 'Problem 197: Investigating the behaviour of a recursively defined sequence'
videoUrl: ''
localeTitle: 问题197：研究递归定义的序列的行为
---
## Description
给定函数f（x）=⌊230.403243784-x2⌋×10-9（⌊⌊是floor函数），序列un由u0 = -1和un + 1 = f（un）定义。 找到n + 1012的un + un + 1.在小数点后面给出9位数的答案。
## Instructions
## Tests
```yml
tests:
- text: euler197()应该返回1.710637717。
testString: 'assert.strictEqual(euler197(), 1.710637717, "euler197() should return 1.710637717.");'
```
## Challenge Seed
```js
function euler197() {
// Good luck!
return true;
}
euler197();
```
## Solution
```js
// solution required
```