64 ??
This is just the answer, if it is the correct one, then I can explain the logic
EDIT:
Certainly it is not the correct answer but still would like to share my point.
There are 8 different ways to solve the 3x3 magic square (having 1-9) problem. Similarly for the one having 10-18 can also be solved by 8 different ways. So combining the two there would be 8x8 = 64 different ways.
Still I believe there will be more... still solving it