用的是埃氏筛。

#include<bits/stdc++.h>

using namespace std;

const int MAX = 9999999;//偶数位必然不是
int prime[MAX + 10];

void ai(){
	for (int i = 2; i <= MAX; i++) {
		prime[i] = 1;
	}
	for (int i = 2; i <= MAX; i++) {
		if (prime[i]) {
			for (int j = i * 2; j <= MAX; j += i){
				prime[j] = 0;
			}	
		}
	}
}
bool check (int x) {
	int a[20];
	int flag = 0;
	while (x) {
		a[flag] = x % 10;
		x /= 10;
		flag ++;
	}
	for (int i = 0;i < flag /2; i++){
		if (a[i] != a[flag - 1 - i])return 0;
	}
	return 1;
}
int main() {
	ai(); 
	int a, b;
	cin >> a >> b;
	for (int i = a; i <= b; i++) {
		if (check(i) && prime[i])cout << i << endl;
	}
	return 0;
}