Prove that the number of $\mathbb{Z}^n$ vectors that their Taxicab norm is not greater than $m$ is equal to the number of $\mathbb{Z}^m$ vectors that their Taxicab norm is not greater than $n$
Let's define a recursive sequence $a(n_1,n_2)$ to count the number of $\mathbb{Z}^{n_2}$ vectors that their Taxicab norm is not greater than $n_1$ If we can find the recursive relation then the rest of it is straightforward. Is there anyone with an idea for $a(n_1,n_2)$?