# Factors of sums and alternating sums of products of $q$-binomial coefficients and powers of $q$-integers

## TL;DR

This paper proves that certain sums involving $q$-binomial coefficients and powers of $q$-integers are Laurent polynomials with integer coefficients, extending divisibility results and confirming conjectures related to $q$-analogues of binomial sums.

## Contribution

The paper establishes new $q$-analogues of divisibility results and confirms conjectures involving sums of $q$-binomial coefficients, advancing the understanding of their algebraic properties.

## Key findings

- Proves sums are Laurent polynomials with integer coefficients.
- Confirms several conjectures of Guo and Zeng.
- Proposes new conjectural congruences for $q$-ballot number sums.

## Abstract

We prove that, for all positive integers $n_1, \ldots, n_m$, $n_{m+1}=n_1$, and non-negative integers $j$ and $r$ with $j\leqslant m$, the following two expressions \begin{align*} &\frac{1}{[n_1+n_m+1]}{n_1+n_{m}\brack n_1}^{-1}\sum_{k=0}^{n_1} q^{j(k^2+k)-(2r+1)k}[2k+1]^{2r+1}\prod_{i=1}^m {n_i+n_{i+1}+1\brack n_i-k},\\[5pt] &\frac{1}{[n_1+n_m+1]}{n_1+n_{m}\brack n_1}^{-1}\sum_{k=0}^{n_1}(-1)^k q^{{k\choose 2}+j(k^2+k)-2rk}[2k+1]^{2r+1}\prod_{i=1}^m {n_i+n_{i+1}+1\brack n_i-k} \end{align*} are Laurent polynomials in $q$ with integer coefficients, where $[n]=1+q+\cdots+q^{n-1}$ and ${n\brack k}=\prod_{i=1}^k(1-q^{n-i+1})/(1-q^i)$. This gives a $q$-analogue of some divisibility results of sums and alternating sums involving binomial coefficients and powers of integers obtained by Guo and Zeng. We also confirm some related conjectures of Guo and Zeng by establishing their $q$-analogues. Several conjectural congruences for sums involving products of $q$-ballot numbers $\left({2n\brack n-k}-{2n\brack n-k-1}\right)$ are proposed in the last section of this paper.