> For the complete documentation index, see [llms.txt](https://dfine.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dfine.gitbook.io/leetcode/866.prime_palindrome.md).

# 866.Prime Palindrome

**866.回文素数**

> 求出大于或等于 N 的最小回文素数。 回顾一下，如果一个数大于 1，且其因数只有 1 和它自身，那么这个数是素数。 例如，2，3，5，7，11 以及 13 是素数。 回顾一下，如果一个数从左往右读与从右往左读是一样的，那么这个数是回文数。 例如，12321 是回文数。

方法，先定义两个函数，一个求回文，一个判断素数。 难点在于超时问题，当n大于11，且n的位数为偶数时，n不可能为回文素数，因此为了缩减时间，将偶数位回文数加一个数量级。

```
class Solution {
public:
    int primePalindrome(int N) {
        if(N<=2)
            return 2;
        if(N%2 ==0 )
            N++;
        while(true)
        {
            if(N > 11 && (int)log10(N)%2)
                N = pow(10,(int)log10(N)+1)+1;
            if(reverse(N) == N &&  palin(N) )
                return N;
            N +=2;
        }
        return -1;

    }
private:
    int reverse(int n)
    {
        int tmp=0;
        while(n)
        {
            tmp = 10*tmp + n%10;
            n /=10;
        }
        return tmp;
    }
    int palin(int n)
    {
        int tmp=sqrt(n);
        for (int i=2; i<=tmp;i++)
            if(n%i==0)
                return 0;
        return 1;
    }
};
```


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://dfine.gitbook.io/leetcode/866.prime_palindrome.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.