题解

#include <bits/stdc++.h>
using namespace std;
const unsigned MAX=1e7+5;
unsigned m=0,cnt=0,ans[MAX],len;
string n;
bool isp(unsigned x){
	if (x<=1) return false;
	for (int i=2;i*i<=x;i++){
		if (x%i == 0) return false;
	}
	return true;
}
bool ispp(unsigned x){
	unsigned s[20],idx=0,k;
	
	while (x){
		s[idx++] = x%10;
		x /= 10;
	}
	for (int i=0;i<idx/2;i++){
		swap(s[i],s[idx-i-1]);
	}
	for (int i=1;i<=idx;i++){
		for (int j=0;j<idx-i+1;j++){
			k=0;
			for (int d=0;d<i;d++){
				k *= 10;
				k += s[j+d];
			}
			if (!isp(k)) return false;
		}
	}
	return true;
}
int main(){
	cin>>n;
	if (n.size()>4){
		n = "373";
	}
	
	len = n.size();
	for (int i=0;i<len;i++) m += pow(10,i)*(n[len-i-1]-'0');
	
	for (int i=2;i<=m;i++){
		if (ispp(i)) ans[cnt++] = i;
	}
	cout<<cnt<<endl;
	for (int i=0;i<cnt;i++){
		cout<<ans[i]<<endl;
	}
	return 0;
}