freeCodeCamp/curriculum/challenges/chinese/10-coding-interview-prep/project-euler/problem-197-investigating-the-behaviour-of-a-recursively-defined-sequence.md

---
id: 5900f4311000cf542c50ff44
title: 'Problem 197: Investigating the behaviour of a recursively defined sequence'
challengeType: 5
forumTopicId: 301835
dashedName: problem-197-investigating-the-behaviour-of-a-recursively-defined-sequence
---

# --description--

Given is the function f(x) = ⌊230.403243784-x2⌋ × 10-9 ( ⌊ ⌋ is the floor-function),

the sequence un is defined by u0 = -1 and un+1 = f(un).

Find un + un+1 for n = 1012. Give your answer with 9 digits after the decimal point.

# --hints--

`euler197()` should return 1.710637717.

```js
assert.strictEqual(euler197(), 1.710637717);
```

# --seed--

## --seed-contents--

```js
function euler197() {

  return true;
}

euler197();
```

# --solutions--

```js
// solution required
```