Filling 2d array in less than O(n^2)?

standard 2d array filling with increasing numbers for rows and columns:

for(int i=0;i<n;i++)
for(int j=0;j<n;j++)
a[i][j] = i + j;

problem is it's O(n^2). I'm looking for a method to decrease the time,
any suggestions? I'm googling for dynamic programming solutions, but
not coming up with much.