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freeCodeCamp/curriculum/challenges/chinese-traditional/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: '問題 145有多少個小於十億的可逆數'
challengeType: 5
forumTopicId: 301774
dashedName: problem-145-how-many-reversible-numbers-are-there-below-one-billion
---
# --description--
一些正整數 $n$ 滿足如下性質:該數與其逆序數之和 [ $n + reverse(n)$ ] 全部由奇數(十進制)組成。 例如,$36 + 63 = 99$ 和 $409 + 904 = 1313$。 我們稱這些數字是可逆的;所以 36、63、409 和 904 均爲可逆的。 無論是 $n$ 還是 $reverse(n)$ 均不允許出現前導零。
小於一千的可逆數有 120 個。
請求出有多少個小於十億(${10}^9$)的可逆數?
# --hints--
`reversibleNumbers()` 應該返回 `608720`
```js
assert.strictEqual(reversibleNumbers(), 608720);
```
# --seed--
## --seed-contents--
```js
function reversibleNumbers() {
return true;
}
reversibleNumbers();
```
# --solutions--
```js
// solution required
```