HDU1719 Friend （数学推导）

friend numbers = 2^x + 3^y -1

#include<stdio.h>
int main()
{
    __int64 a;
    while(scanf("%I64d",&a)!=EOF)
    {
        if(!a) 
        {
            printf("NO!
");
            continue;
        }
        a+=1;
        while(a%2==0||a%3==0)
        {
            if(a%2==0) a/=2;
            if(a%3==0) a/=3;         
        }   
        if(a==1) printf("YES!
");
        else printf("NO!
");                      
    }    
}