Let \(G = (V, E)\) be a graph. The Gutman-Milovanović index of a graph \(G\) is defined as \(\sum\limits_{uv \in E} (d(u) d(v))^{\alpha}(d(u) + d(v))^{\beta}\), where \(\alpha\) and \(\beta\) are any real numbers and \(d(u)\) and \(d(v)\) are the degrees of vertices \(u\) and \(v\) in \(G\), respectively. In this note, we present sufficient conditions based on the Gutman-Milovanović index with \(\alpha > 0\) and \(\beta >0\) for some Hamiltonian properties of a graph. We also present upper bounds for the Gutman-Milovanović index of a graph for different ranges of \(\alpha\) and \(\beta\).

Suppose \(G_1=(V_1, E_1)\) is a graph and \(G_2=(V_2, E_2)\) is a strong digraph of \(G_1\), where \(V_1\) and \(V_2\) represent the vertex sets, \(E_1\) and \(E_2\) represent the edge sets. Let \(u\) and \(v\) be any two vertices of \(G_2\). The strong distance \(sd(u,v)\) is the minimum value of edges in a strong subdiagraph of \(G_2\) that contains \(u\) and \(v\). The minimum strong diameter of \(G_2\) is defined as the maximum eccentricity \(se(u)\) from \(u\) to all other vertices in \(G_2\). In this paper, we propose different strong orientation methods to explore the minimum strong diameter of the strong product graph of \(K_{m_1,m_2,\ldots,m_k}\otimes P_n\), where \(K_{m_1,m_2,\ldots,m_k}\) and \(P_n\) represent respectively complete multipartite graph and path. ‌‌In addition, based on strong orientation methods, a new algorithm is proposed to model the presence or absence of a minimum strong diameter in a strong product graph. Simulation experiments show a trend of simultaneous decrease and concentration in the minimum strong diameter of the strong product graph, as the value of parts in \(K_{m_1,m_2,\ldots,m_k}\) increases while the length of \(P_n\) remains constant.

We consider a joint ordered multifactorisation for a given positive integer \(n\geq 2\) into \(m\) parts, where \(n=n_1~\times~\ldots~\times~n_m\), and each part \(n_j\) is split into one or more component factors. Our central result gives an enumeration formula for all such joint ordered multifactorisations \(\mathcal{N}_m(n)\). As an illustrative application, we show how each such factorisation can be used to uniquely construct and so count the number of distinct additive set systems (historically referred to as complementing set systems). These set systems under set addition generate the first \(n\) non-negative consecutive integers uniquely and, when each component set is centred about 0, exhibit algebraic invariances. For fixed integers \(n\) and \(m\), invariance properties for \(\mathcal{N}_m(n)\) are established. The formula for \(\mathcal{N}_m(n)\) is comprised of sums over associated divisor functions and the Stirling numbers of the second kind, and we conclude by deducing sum over divisor relations for our counting function \(\mathcal{N}_m(n)\). Some related integer sequences are also considered.

In this work we study the acyclic orientations of graphs. We obtain an encoding of the acyclic orientations of the complete \(p\)-partite graph with size of its parts \(n_1,n_2,\ldots,n_p\) via a vector with \(p\) symbols and length \(n=n_1+n_2+\ldots+n_p\) when the parts are fixed but not the vertices in each part. We also give a recursive way to construct all acyclic orientations of a complete multipartite graph, this construction can be done by computer easily in order \(\mathcal{O}(n)\). Furthermore, we obtain a closed formula for non-isomorphic acyclic orientations of both the complete multipartite graphs and the complete multipartite graphs with a directed spanning tree. Moreover, we obtain a closed formula for the number of acyclic orientations of a complete multipartite graph \(K_{n_1,\ldots,n_p}\) with labelled vertices. Finally, we obtain a way encode all acyclic orientations of an arbitrary graph as a permutation code. Using the codification mentioned above we obtain sharp upper and lower bounds of the number of acyclic orientations of a graph.

In this work, we defined almost neo balancing numbers and determined the general terms of them in terms of balancing and Lucas-balancing numbers. We also deduced some results on relationship with triangular, square triangular, Pell, Pell-Lucas numbers and these numbers. Further we formulate the sum of first \(n\)-terms of these numbers.

Let \(G\) be a graph with vertex set \(V(G) = \{v_1, v_2, \dots, v_n\}\). We associate to \(G\), a matrix \(P(G)\) whose \((i, j)\)-th entry is the maximum number of vertex-disjoint paths between the corresponding vertices if \(i\neq j\), and is zero otherwise. We call this matrix the path matrix of \(G\), and its eigenvalues are referred to as the path eigenvalues of \(G\). In this paper, we investigate the path eigenvalues of graphs resulting from certain graph operations and specific graph families.

Null graphs (respectively, 1-regular graphs) are the only regular graphs with local antimagic chromatic number 1 (respectively, undefined). In this paper, we proved that the join of 1-regular graph and a null graph has local antimagic chromatic number 3. As a by-product, we also obtained many families of (possibly disconnected or regular) bipartite and tripartite graph with local antimagic chromatic number 3.

Let \(G = (V, E)\) be a graph with vertex set \(V\) and edge set \(E\). A vertex set \(S \subset V\) is a perfect dominating set if every vertex in \(V – S\) is adjacent to exactly one vertex in \(S\). A perfect dominating set \(S\) is furthermore: (i) an efficient dominating set or a \(1\)-efficient dominating set if no two vertices in \(S\) are adjacent, (ii) a total efficient dominating set or a \(2\)-efficient dominating set if every vertex in \(S\) is adjacent to exactly one other vertex in \(S\), and (iii) a \(1,2\)-efficient dominating set if every vertex in \(S\) either adjacent to no vertices in \(S\) or to exactly one other vertex in \(S\). In this paper we introduce the concept of \(1,2\)-efficiency in graphs and apply it to the existence of \(1,2\)-efficient sets in grid graphs \(G_{m,n}\), that is, graphs resembling chessboards having a rectangular array of \(m \times n\) vertices arranged into \(m\) rows of \(n\) vertices, or \(n\) columns of \(m\) vertices. It is well known that almost no grid graphs are \(1\)-efficient, and relatively few grid graphs are \(2\)-efficient. However, in this paper, we show that all but a relatively small percentage of grid graphs are \(1,2\)-efficient.

onsidering regions in a map to be adjacent when they have nonempty intersection (as opposed to the traditional view requiring intersection in a linear segment) leads to the concept of a facially complete graph: a plane graph that becomes complete when edges are added between every two vertices that lie on a face. Here we present a complete catalog of facially complete graphs: they fall into seven types. A consequence is that if \(q\) is the size of the largest face in a plane graph \(G\) that is facially complete, then \(G\) has at most \(\left\lfloor 3q/2\right\rfloor\) vertices. This bound was known, but our proof is completely different from the 1998 approach of Chen, Grigni, and Papadimitriou (Planar map graphs, Proc. 30th ACM Symp. Th. of Computing, 514–523). Our method also yields a count of the 2-connected facially complete graphs with \(n\) vertices. We also show that if a plane graph has at most two faces of size 4 and no larger face, then the addition of both diagonals to each 4-face leads to a graph that is 5-colorable.

A bowtie graph is the union of two edge disjoint 3-cycles which share a single vertex. A mixed bowtie is a partial orientation of a bowtie graph. In this paper, we consider decompositions of the complete mixed graph into mixed bowties consisting of a union of two isomorphic copies of mixed triples.