1 and 9.
3 9 2 1
6 3
7 4
9 8 1 7
Going clockwise, each digit is the sum of the previous two, on a mod 10 scale (look only at the ones digit of a sum).
For example, 6+3=9, then 3+9=2 (12-10), 9+2=1, and so on.
The square has some other interesting properties, for example, each pair of digits directly across from each other (6 numbers apart) add up to 10.
Other explanations, yielding both the intended result and varied solutions, can be found in the problem comments. |
