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freeCodeCamp/curriculum/challenges/chinese/10-coding-interview-prep/project-euler/problem-145-how-many-reversible-numbers-are-there-below-one-billion.md

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---
id: 5900f3fd1000cf542c50ff10
title: '问题 145有多少个小于十亿的可逆数'
challengeType: 5
forumTopicId: 301774
dashedName: problem-145-how-many-reversible-numbers-are-there-below-one-billion
---
# --description--
一些正整数 $n$ 满足如下性质:该数与其逆序数之和 [ $n + reverse(n)$ ] 全部由奇数(十进制)组成。 例如,$36 + 63 = 99$ 和 $409 + 904 = 1313$。 我们称这些数字是可逆的;所以 36、63、409 和 904 均为可逆的。 无论是 $n$ 还是 $reverse(n)$ 均不允许出现前导零。
小于一千的可逆数有 120 个。
请求出有多少个小于十亿(${10}^9$)的可逆数?
# --hints--
`reversibleNumbers()` 应该返回 `608720`
```js
assert.strictEqual(reversibleNumbers(), 608720);
```
# --seed--
## --seed-contents--
```js
function reversibleNumbers() {
return true;
}
reversibleNumbers();
```
# --solutions--
```js
// solution required
```