This problem is difficult. Use the sieve method and strengthen it. After multiplying the prime factors of each number and sorting them, you can determine the next order.
2 4 8 16 32 ........3 6 9
So if the next prime factor multiplication is not the same as the previous one, it means that it has exceeded the MAX range.
//============================================================================
// Name : Next Same-Factored.cpp
// Date : 2013/3/30 上午12:42:53
// Author : GCA
//============================================================================
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <climits>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cctype>
#include <utility>
using namespace std;
#ifdef ONLINE\_JUDGE
#define ll "%lld"
#else
#define ll "%I64d"
#endif
typedef unsigned int uint;
typedef long long int Int;
#define Set(a,s) memset(a,s,sizeof(a))
#define Write(w) freopen(w,"w",stdout)
#define Read(r) freopen(r,"r",stdin)
#define Pln() printf("\\n")
#define I\_de(x,n)for(int i=0;i<n;i++)printf("%d ",x\[i\]);Pln()
#define De(x)printf(#x"%d\\n",x)
#define For(i,x)for(int i=0;i<x;i++)
#define CON(x,y) x##y
#define Pmz(dp,nx,ny)for(int hty=0;hty<ny;hty++){for(int htx=0;htx<nx;htx++){\\
printf("%d ",dp\[htx\]\[hty\]);}Pln();}
#define M 2000001
#define PII pair<int,int\>
#define PB push\_back
#define oo INT\_MAX
#define Set\_oo 0x3f
#define Is\_debug true
#define debug(...) if(Is\_debug)printf("DEBUG: "),printf(\_\_VA\_ARGS\_\_)
#define FOR(it,c) for(\_\_typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define eps 1e-6
bool xdy(double x,double y){return x>y+eps;}
bool xddy(double x,double y){return x>y-eps;}
bool xcy(double x,double y){return x<y-eps;}
bool xcdy(double x,double y){return x<y+eps;}
int min3(int x,int y,int z){
int tmp=min(x,y);
return min(tmp,z);
}
int max3(int x,int y,int z){
int tmp=max(x,y);
return max(tmp,z);
}
struct nums{
int primesum;
int all;
int tmp;
}num\[M\];
int sid\[M\];
bool cmp(nums a,nums b){
if(a.primesum<b.primesum){
return true;
}else if(a.primesum>b.primesum){
return false;
}else{
return a.all<b.all;
}
}
int main() {
ios\_base::sync\_with\_stdio(0);
for(int i=0;i<M;i++){
num\[i\].tmp=num\[i\].all=i;
num\[i\].primesum=1;
}
for(int i=2;i<M;i++){
if(num\[i\].all==num\[i\].tmp){
num\[i\].primesum=i;
for(int prime=(i<<1);prime<M;prime+=i){
num\[prime\].primesum\*=i;
num\[prime\].tmp/=i;
}
}
}
sort(num,num+M,cmp);
for(int i=0;i<M;i++){
sid\[num\[i\].all\]=i;
// debug("%d",num\[i\].all);
}
int n;
while(~scanf("%d",&n)){
if(n==0||n==1){
puts("Not Exist!");
continue;
}
n=sid\[n\];
// debug("%d",num\[n+1\].all);
if(num\[n\].primesum==num\[n+1\].primesum){
if(num\[n+1\].all<=2000000)
printf("%d\\n",num\[n+1\].all);
else puts("Not Exist!");
}else puts("Not Exist!");
}
}