10
Jelly, 2 bytes
»þ
Try it online!
Outputs an n x n matrix. If the output format is required, 4 bytes
This is simply a table of maximums. For each cell \$A_{i,j}\$ in the output, the result is equal to \$\max(i,j)\$. The 4 byte answer has ` to reuse the argument, and G to format the output as a gr...