A number square contains all numbers from 1 to n^2 without duplicates.
The 2 X 2 subset diagonal sums in these squares are equal, though those sums may differ.
When the single unit 2 X 2 subset is required to have diagonals with equal sums every rectangle within the generated square will have diagonals with equal sums.
Reversible squares are a previously defined entity. They require all symmetrically opposite pairs in each row and column to have the same sum in addition to the diagonal constraints noted above.
It is an embarrassment that no one has enumerated the order 6 magic squares. Richard C. Schroeppel provided the exact count for the order 5 magic squares in 1973 - now more than 40 years ago.
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