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Each row is an arithmetic progression with the initial term a₁ = 2, common difference d = 1 and the number of terms n = y. The sum of the first n terms of arithmetic progression is (n/2)(2a₁ + (n-1)d) = (y/2)(4 + y - 1) = y(y + 3)/2. Since there are x rows, the sum of all values in the matrix is xy(y + 3)/2.
Here are several remarks.