It is known that the polynomial $f(n,m)=\frac{1}{2}(n+m)(n+m+1)+m$ defines bijection $\mathbb{N}\times\mathbb{N}\to\mathbb{N}$ (Put pairs of $\mathbb{N}$ into the semiinfinite matrix and count them by diagonals). Does there exist a polynomial bijection $\mathbb{Z}\times\mathbb{Z}\to\mathbb{Z}$? The question is related to the open question about polynomial bijection $\mathbb{Q}\times\mathbb{Q}\to\mathbb{Q}$ here.

5$\begingroup$ Related but not decisive: thehcmr.org/issue1_2/bert_and_ernie.pdf $\endgroup$ – Benjamin Dickman Dec 28 '12 at 6:53

6$\begingroup$ [It's also AMM 6028, which remains unsolved as far as I know.] $\endgroup$ – Benjamin Dickman Dec 28 '12 at 7:02

4$\begingroup$ @Dickman: It took a me a while to know what you were talking about. Let me add the link books.google.es/books?id=KX6D6hefyA0C&pg=217 $\endgroup$ – boumol Dec 28 '12 at 11:44

6$\begingroup$ @Dicman and @Boumol: Thank you for interesting references. Interesting, AMM6028 asks for polynomials with integer coefficients. In fact, the bijection $\mathbb{N}\times\mathbb{N}\to\mathbb{N}$ I know has rational coefficients. Does there exist polynomial $\mathbb{N}\times\mathbb{N}\to\mathbb{N}$ bijection with integer coefficients? $\endgroup$ – Lev Glebsky Dec 28 '12 at 18:32

3$\begingroup$ Updated: zacharyabel.com/papers/FavoriteProblem_A07_HCMR.pdf $\endgroup$ – Steve D Mar 9 '16 at 22:09
It is an open problem. Maximal results about bijections from $\mathbb N\times \mathbb N$, $\mathbb Z\times \mathbb N$, $\mathbb Z\times \mathbb Z$ to $\mathbb N$ are contained in
John S. Lew, Arnold L. Rosenberg, Polynomial indexing of integer latticepoints I. General concepts and quadratic polynomials, J. Number Theory 10 (1978) pp 192214, doi:10.1016/0022314X(78)900355.
Polynomial indexing of integer latticepoints II. Nonexistence results for higherdegree polynomials, J. Number Theory 10 (1978) pp 215243, doi:10.1016/0022314X(78)900367