Friend number are defined recursively as follows.
(1) numbers 1 and 2 are friend number;
(2) if a and b are friend numbers, so is ab+a+b;
(3) only the numbers defined in (1) and (2) are friend number.
Now your task is to judge whether an integer is a friend number.
There are several lines in input, each line has a nunnegative integer a, 0<=a<=2^30.
For the number a on each line of the input, if a is a friend number, output “YES!”, otherwise output “NO!”.
//考查知识点:数学推导。。
#include<stdio.h>
int main()
{
int n;
while(~scanf("%d",&n))
{
if(n==0)
{
printf("NO!\n");
continue;
}
n++;
while(n%3==0||n%2==0)
{
if(n%3==0)
n/=3;
if(n%2==0)
n/=2;
}
if(n==1)
printf("YES!\n");
else
puts("NO!");
}
return 0;
}