任意一个4位自然数（除4个数字完全一样除外，例如4444、7777等），，将组成该数的各位数字重新排列，形成一个最大数和一个最小数，之后两数相减，其差仍然为一个自然数，重复上述运算，你会发现一个神秘数。-Any of a four natural numbers (with the exception of the four numbers exactly the same, except such as 4444,7777, etc.), will form the digits of the number of re-arranged to form one of the greatest number and a minimum number after two the number of subtraction, the difference still is a natural number, repeat the above computation, you will find a mysterious number.