天体物理中的黑洞现象在数学中也存在,并被叫做“数学黑洞”。所谓数学黑洞是这样一类数,其他任意的数如果经过某种变换变成这个数以后,再按同样的规律变化时,最后得到的始终都是这个数,再也跳不出去了。我们今天就一起来研究一下这样一类有趣的数——黑洞数。1.四位数的黑洞数随意写出一个四位数,它的各个数位上的数字不都相等(11 11,2222,3333等四位数应排除),用这个四位数各个数位上的数字组成一个最大数和一个最小数,并用最大数减去最小数,得到一个新的四位数(如果差等于 The phenomenon of black hole in astrophysics also exists in mathematics and is called “math black hole”. The so-called math black hole is such a number, if any other number after some transformation into this number, according to the same rules change, the last is always get the number, never jump out. Today we work together to study such a class of interesting numbers - the number of black holes. 1. Four-digit black holes Free to write a four-digit number, its numbers are not all the same numbers (11 11,2222,3333 and other four-digit should be excluded), with the four-digit on each digit The numbers make up a maximum number and a minimum number, and subtract the minimum number from the maximum number to get a new four-digit number (if the difference is equal to