Since ancient times, mathematicians have considered geometrical objects with integral side lengths. We consider plane integral point sets \(P\), which are sets of \(n\) points in the plane with pairwise integral distances, where not all the points are collinear.

The largest occurring distance is called its diameter. Naturally, the question about the minimum possible diameter \(d(2, 7)\) of a plane integral point set consisting of \(7\) points arises. We give some new exact values and describe state-of-the-art algorithms to obtain them. It turns out that plane integral point sets with minimum diameter consist very likely of subsets with many collinear points. For this special kind of point sets, we prove a lower bound for \(d(2, n)\) achieving the known upper bound \(n^{c_2\log \log n }\) up to a constant in the exponent.
A famous question of Erdés asks for plane integral point sets with no \(3\) points on a line and no \(4\) points on a circle. Here, we talk of point sets in general position and denote the corresponding minimum diameter by \(d(2,n)\). Recently \(d(2, 7) = 22270\) could be determined via an exhaustive search.

In this paper, we study invariant sequences by umbral method, and give some identities which are similar with the identities of Bernoulli numbers.

In this paper, we consider the total domination number, the restrained domination number, the total restrained domination number and the connected domination number of lexicographic product graphs.

In this paper, we obtain the numbers of embeddings of wheel graphs on some orientable and nonorientable surfaces of small genera, mainly on torus, double torus, and nonorientable surfaces of genus \(1, 2, 3\), and \(4\). These are the first results for embeddings of wheel graphs on nonorientable surfaces as known up to now.

An \((a, d)\)-edge-antimagic total labeling for a graph \(G(V, E)\) is an injective mapping \(f\) from \(V \cup E\) onto the set \(\{1, 2, \ldots, |V| + |E|\}\) such that the set \(\{f(v) + \sum f(uv) \mid uv \in E\}\), where \(v\) ranges over all of \(V\), is \(\{a, a+d, a+2d, \ldots, a+(|V|-1)d\}\). Simanjuntak et al conjecture:1. \(C_{2n}\) has a \((2n + 3, 4)\)- or a \((2n + 4, 4)\)-edge-antimagic total labeling;
2. cycles have no \((a, d)\)-edge-antimagic total labelings with \(d > 5\).In this paper, these conjectures are shown to be true.

This article discusses the geometricity of the direct sum, direct product and lexicographic products of two lattices, and compute their characteristic polynomials and classify their geometricity.

This paper introduces the concepts of a \({supergraph}\) and \({graphical\; complexity}\) of a permutation group, intended as a tool for investigating the structure of concrete permutation groups. Basic results are established and some research problems suggested.

We given a two parameter generalization of identities of Carlitzand Gould involving products of binomial coefficients. The generalization involves Jacobi polynomials.

Consider a connected undirected graph \(G = (V, E)\) and an integer \(r \geq 1\). For any vertex \(v \in V\), let \(B_r(v)\) denote the ball of radius \(r\) centered at \(v\), i.e., the set of all vertices linked to \(v\) by a path of at most \(r\) edges. If for all vertices \(v \in V\), the sets \(B_r(v)\) are different, then we say that \(G\) is \(r\)-twin-free.

Studies have been made, e.g., on the number of edges or the minimum degree in one-twin-free graphs. We extend these investigations and in particular we determine the exact size of the largest clique in a connected \(r\)-twin-free graph.

Let \(D\) be a strongly connected digraph with order at least two. Let \(M(D)\) denote the middle digraph of \(D\), and let \(\kappa(D)\) and \(\lambda(D)\) denote the connectivity and arc-connectivity of \(D\), respectively. In this paper, we study super-arc-connected and super-connected middle digraphs and the spectrum of middle digraphs.