The Mystical Numbers

The Mystical Numbers are the number that fit and pair with each other, and meant to be with the other number, some say that if we do this pair, we got a good number. Believe it or not, it's up to you.

0-1
1-0
2-5
3-8
4-7
5-2
6-9
7-4
8-3
9-6
 

For example: "5247"