An grid is labeled with consecutive rows and columns so that it is filled with integers from 1 to , inclusive, and the sum of all of the numbers in row and in column are both divisible by . Find the number of possible distinct grids.
Solution
We begin by filling the 10 by 10 grid formed by rows and columns 1 through 10 with any values, which we can do in ways. Then in column 0, there is at most 1 way to fill in the square in row 10, 2 ways for the square in row 9, down to ways in row 0. Similarly, there is 1 way to fill in the square in row 0 and column 10, 2 ways to fill in the square in row 0 and column 9, etc. Overall, the number of ways to fill out the squares in row or column 0 is , so the number of possible distinct grids .
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