At first glance, it might not seem so obvious but, as you are about to see, anyone who can subtract can uncover the mystery that makes 6174 so special.

In 1949, mathematician D.R. Kaprekar from Devlali, India, devised the process now known as Kaprekar’s Operation. Here’s how it works:

First, choose a four digit number where the digits are not all the same (that is, not 1111, 2222 …). Next, rearrange the digits to get the largest and smallest numbers these digits can make. Finally, subtract the smallest number from the largest to get a new number and repeat the operation for each new number. … continue reading