Nonnegativity conjecture for the qq-binomial quotient Gk,n(q)G_{k,n}(q)

For k,nN0k,n\in\mathbb{N}_0, define Gk,n(q)G_{k,n}(q) by

Fk,1(q)=n0Gk,n(q)qn+1,Gk,n(q)=11q2n+1[2k+2n22n]q[k+n1 ]q2.F_{k,1}(q)=\sum_{n\ge 0}G_{k,n}(q)q^{n+1},\qquad G_{k,n}(q)=\frac{1}{1-q^{2n+1}}\frac{\begin{bmatrix}2k+2n-2\\2n\end{bmatrix}_{q}}{\begin{bmatrix}k+n-1\ \end{bmatrix}_{q^2}}.

Here [a\b]q\begin{bmatrix}a\b\end{bmatrix}_q denotes the qq-binomial coefficient, and A(q)0A(q)\succeq0 means that all coefficients of A(q)A(q) are nonnegative. Nonnegativity conjecture for Gk,n(q)G_{k,n}(q). One has Gk,n(q)0G_{k,n}(q)\succeq0. This is a refinement of the m=1m=1 positivity conjecture and would imply it; the source presents it as an open conjecture supported by the displayed quotient and computational evidence.

Sources & referencesView supporting material

Primary source

Koustav Banerjee, Kathrin Bringmann and William J. Keith, “On a conjecture of Andrews and Bachraoui”, arXiv:2601.04014 (2026).

Additional references

3 papers in this index state this conjecture (2013–2026). The statement above is taken from the most recent of them; the others are arXiv:2306.09450, arXiv:1312.7548.

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