Feel like having your mind blown?  Try this little exercise:

Choose any number with 4 non-repeating digits. Say 7182.

1. Arrange the number in ascending and then descending order
2. Subtract the smaller number from the bigger number (8721 – 1278 = 7443)
3. Repeat steps 1-2 with the result:
   1. 7443 – 3447 = 3996
   2. 9963 – 3699 = 6264
   3. 6642 – 2466 = 4176
   4. 7641 – 1467 = 6174

Go ahead – try any 4-digit number with non-repeating digits. You’ll always get 6174.

6174 is known as Kaprekar’s constant. The math operation above, discovered by Indian mathematician D.R. Kaprekar, will reach 6174 after at most 7 steps (if it took you more than 7 iterations to reach 6174, check your math).