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arXiv · 2605.01565

Vertex connectivity of the nonzero nonunit core of the comaximal graph of $\mathbb Z_n$

Bilal Ahmad Rather
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Abstract

This article settles Problem 7.2 posed by [Banerjee, Special Matrices (2022)] for the induced subgraph $G_2$ of the comaximal graph $\Gamma(\mathbb Z_n)$ when $n$ is squarefree. Let $n=p_1p_2\cdots p_m$ with distinct primes $p_1<\cdots<p_m$, and let $G_2$ be the graph on the nonzero nonunit residue classes modulo $n$. We use Chinese remainder representation of $\mathbb Z_n$, and encodes each vertex by the set of vanishing coordinates. This converts $G_2$ into a weighted blow-up of a disjointness graph on nonempty proper subsets of $\{1,\dots,m\}$. Within this model, we derive exact class sizes, explicit degree formulas, the minimum-degree layer, and a short-path criterion. The main theorem proves the connectivity of $G_{2}$ as $\kappa(G_2)=\prod_{i=1}^{m-1}(p_i-1)=\tfrac{\phi(n)}{p_m-1}$. Consequently, earlier upper bound is sharp, $G_2$ is maximally connected, and its edge connectivity agrees with its minimum degree. We also obtain distance formulas, diameter and radius information, and a linear-time algorithm once the prime factorization is known.

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BibTeXRIS

Bilal Ahmad Rather. 2026-05-02. Vertex connectivity of the nonzero nonunit core of the comaximal graph of $\mathbb Z_n$. https://arxiv.org/abs/2605.01565

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