题目9：一个数如果恰好等于它的因子之和，这个数就称为“完数”。例如6=1＋2 ＋3.编程找出1000以内的所有完数。-Title 9: if just a number is equal to the sum of its factor, the number is called "the number". For example 6 = 1+ 2 + 3. Programming to find out all the 1000 less than the number.