数列对的问题,如何运用C语言的方式作答,利用C语言如何解决这个问题

Problem Description
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.

Input
There are several lines in input, each line has a nunnegative integer a, 0<=a<=2^30.

Output
For the number a on each line of the input, if a is a friend number, output “YES!”, otherwise output “NO!”.

Sample Input
3
13121
12131

Sample Output
YES!
YES!
NO!