Magic Square
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Give an n by n grid place the numbers 1 to n^2 in the grid
such that every row, column and diagonal adds up to the same amount.

Example:

> mzn-gecode magic.mzn -D"n=3"
2 7 6
9 5 1
4 3 8

> mzn-gecode magic.mzn -D"n=4"
4 9 6 15
5 16 3 10
11 2 13 8
14 7 12 1


Question
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(a) For n=3, is the middle square always 5? Suggest two ways to answer this question.
(b) How long (in nodes & runtime) did it take you to find magic with n = 6?


History & Fun
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Start here https://en.wikipedia.org/wiki/Magic_square 


Patrick