Black Hole Numbers This afternoon, I looked at my Olympic math book. It had an interesting story after each section of the book. I read an interesting one about black hole numbers: Take any natural number, and split it into three parts, one part is for the odd numbers, one is for the even numbers, and another is for the sum of the number of odd and even numbers. For example, use 892,102,345 (it’s not the same as the book). There are 5 even numbers and 4 odd numbers, and the sum is 9. So we get 549. Then repeat doing that. There is 1 even number and 2 odd numbers. Then you get 123. After that, you can’t do anything. Then use another number, 296. There are 2 even numbers and 1 odd number. 2+1=3, so you get 213. There is 1 even number and 2 odd numbers, and the sum is 3. At last, you get 123 too! Some people say maybe it’s just a coincidence. Use 8 as an example. 1 even number, 0 odd numbers, and get 101. Then, there is 1 even number and 2 odd numbers in 101. At last, you always get 123! You can never leave 123 in this rule; mathematics is fun, isn’t it?