Problem 45578. Create a matrix that counts up diagonally

Given a single input N, create a N x N matrix that counts from 1 : N ², (along up-right diagonals, starting with 1 in the top left corner. For example, given N=4...

1  3  6 10
2  5  9 13 
4  8 12 15 
7 11 14 16

Notice as you move up a row and right a column (↗) the values always increase by one. The value '1' should always go in the top left corner, with '2' directly below it. From there fill in the upward-rightward diagonals with the next higher integer until the matrix is complete. Assume N will always be a positive integer greater than 1 (N >= 2).