In this paper, the class of \((m,n)\)-ary hypermodules is introduced and several properties and examples are found. \((m,n)\)-ary hypermodules are a generalization of hypermodules. On the other hand, we can consider \((m,n)\)-ary hypermodules as a good generalization of \((m,n)\)-ary modules. We define the fundamental relation \(\epsilon^*\) on the \((m,n)\)-ary hypermodules \(M\) as the smallest equivalence relation such that \(M/\epsilon^*\) is an \((m,n)\)-ary module, and then some related properties are investigated.

For given graphs \(G_1\) and \(G_2\), the Ramsey number \(R(G_1, G_2)\) is defined to be the least positive integer \(n\) such that every graph \(G\) on \(n\) vertices, either \(G\) contains a copy of \(G_1\) or the complement of \(G\) contains a copy of \(G_2\). In this note, we show that \(R(C_m, B_n) = 2m-1\) for \(m \geq 2n-1 \geq 7\). With the help of computers, we obtain the exact values of \(14\) small cycle-book Ramsey numbers.

For positive integers \(c \geq 0\) and \(k \geq 1\), let \(n = R(c, k)\) be the least integer, provided it exists, such that every \(2\)-coloring of the set \([1,n] = \{1,\ldots,n\}\) admits a monochromatic solution to the equation \(x + y+c = 4z\) with \(x, y, z \in [1,n]\). In this paper, the precise value of \(R(c, 4)\) is shown to be \(\left\lceil{3c + 2}/{8}\right\rceil\) for all even \(c \geq 34\).

Given a positive integer \(n\) such that \(-1\) is a quadratic residue mod \(n\), we give an algorithm that computes the integers \(u\) and \(v\) which satisfy the equation \(n = u^2 + v^2\). To do this, we use the group structure of the Modular group \(\Gamma= \text{PSL}(2,\mathbb{Z})\).

For a graph \(G = (V(G),E(G))\), a set \(S \subseteq V(G)\) is called a dominating set if \(N_G[S] = V(G)\). A dominating set \(S\) is said to be minimal if no proper subset \(S’ \subset S\) is a dominating set. Let \(\gamma(G)\) (called the domination number) and \(\Gamma(G)\) (called the upper domination number) be the minimum cardinality and the maximum cardinality of a minimal dominating set of \(G\), respectively. For a tree \(T\) of order \(n \geq 2\), it is obvious that \(1 = \gamma(K_{1,n-1}) \leq \gamma(T) \leq \Gamma(T) \leq \Gamma(K_{1,n-1}) = n-1\). Let \(t(n) = \min_{|T|=n}(\Gamma(T)-\gamma(T))\). In this paper, we determine \(t(n)\) for all natural numbers \(n\). We also characterize trees \(T\) with \(\Gamma(T) – \gamma(T) = t(n)\).

The signless \(r\)-associated Stirling numbers of the first kind \(d_r(n, k)\) counts the number of permutations of the set \(\{1,2,\ldots,n\}\) that have exactly \(k\) cycles, each of which is of length greater than or equal to \(r\), where \(r\)is a fixed positive integer. F. Brenti obtained that the generating polynomials of the numbers \(d_r(n, k)\) have only real zeros. Here we consider the location of zeros of these polynomials.

A kite-design of order \(n\) is a decomposition of the complete graph \(K_n\) into kites. Such systems exist precisely when \(n \equiv 0,1 \pmod{8}\). Two kite systems \((X,\mathcal{K}_1)\) and \((X,\mathcal{K}_2)\) are said to intersect in \(m\) pairwise disjoint blocks if \(|\mathcal{K}_1 \cap \mathcal{K}_2| = m\) and all blocks in \(\mathcal{K}_1 \cap \mathcal{K}_2\) are pairwise disjoint. In this paper, we determine all the possible values of \(m\) such that there are two kite-designs of order \(n\) intersecting in \(m\) pairwise disjoint blocks, for all \(n \equiv 0,1 \pmod{8}\).

In this note, we present some upper bounds for the \(k\)th largest eigenvalue of the adjacency matrix as well as the Laplacian matrix of graphs. Special attention is paid to the Laplacian matrix of trees.

Let \(P(G, \lambda)\) denote the chromatic polynomial of a graph \(G\). Two graphs \(G\) and \(H\) are chromatically equivalent, written \(G \sim H\), if \(P(G, \lambda) = P(H, \lambda)\). A graph \(G\) is chromatically unique, written \(x\)-unique, if for any graph \(H\), \(G \sim H\) implies that \(G\) is isomorphic with \(H\). In this paper, we prove that the graph \(\theta(a_1, a_2, \ldots, a_6)\) is \(x\)-unique for exactly two distinct values of \(a_1, a_2, \ldots, a_6\).

In this paper, we give an explicit expression of the genus distributions of \(M_j^n\), for \(j = 1, 2, \ldots, 11\), which are introduced in the previous paper “Orientable embedding distributions by genus for certain types of non-planar graphs”. For a connected graph \(G = (V, E)\) with a cycle, let \(e\) be an edge on a cycle. By adding \(2n\) vertices \(u_1, u_2,u_3 \ldots, u_n, v_1, v_2,v_3 \ldots, v_n\) on \(e\) in sequence and connecting \(u_k, v_k\) for \(1 \leq k \leq n\), a non-planar graph \(G_n\) is obtained for \(n \geq 3\). Thus, the orientable embedding distribution of \(G_n\) by genus is obtained via the genus distributions of \(M_j^n\).