In \([5]\), a product summation of ordered partition \(f(n,m,r) = \sum{c_1^r + c_2^r + \cdots + c_m^r }\) was defined, where for two given positive integers \(m,r\), the sum is over all positive integers \(c_1, c_2, \ldots, c_m\) with \(c_1 + c_2 + \cdots + c_m = n\). \(f(n,r) = \sum_{i=1}^n f(n,m,r)\) was also defined. Many results on \(f(n,m,r)\) were found. However, few things have been known about \(f(n,r)\). In this paper, we give more details for \(f(n,r)\), including its two recurrences, its explicit formula via an entry of a matrix and its generating function. Unexpectedly, we obtain some interesting combinatorial identities, too.

In this paper, we obtain new general results containing sums of binomial and multinomial with coefficients satisfying a general third order linear recursive relations with indices in arithmetic progression.

The closed neighborhood \(N[e]\) of an edge \(e\) in a graph \(G\) is the set consisting of \(e\) and of all edges having a common end-vertex with \(e\). Let \(f\) be a function on \(E(G)\), the edge set of \(G\), into the set \(\{-1,1\}\). If \(\sum_{e \in N[e]} f(x) \geq 1\) for each \(e \in E(G)\), then \(f\) is called a signed edge dominating function of \(G\). The minimum of the values \(\sum_{e \in E(G)} f(e)\), taken over all signed edge dominating functions \(f\) of \(G\), is called the signed edge domination number of \(G\) and is denoted by \(\gamma’_s(G)\). It has been conjectured that \(\gamma’_s(T) \geq 1\) for every tree \(T\). In this paper we prove that this conjecture is true and then classify all trees \(T\) with \(\gamma’_s(T) = 1,2\) and \(3\).

This article is a contribution to the study of block-transitive automorphism groups of \(2\)-\((v,k,1)\) block designs. Let \(\mathcal{D}\) be a \(2\)-\((v,k,1)\) design admitting a block-transitive, point-primitive but not flag-transitive group \(G\) of automorphisms. Let \(k_1 = (k, v-1)\) and \(q = p^f\) for prime \(p\). In this paper we prove that if \(G\) and \(D\) are as above and \(q > {(2(k_rk-k_r+1)f)^{\frac{1}{4}}}\) then \(G\) does not admit a Chevalley group \(E_7(q)\) as its socle.

A graph \(G\) is called super edge-magic if there exists a bijection \(f\) from \(V(G) \cup E(G)\) to \(\{1, 2, \ldots, |V(G)| + |E(G)|\}\) such that \(f(u) + f(v) + f(uv) = C\) is a constant for any \(uv \in E(G)\) and \(f(V(G)) = \{1, 2, \ldots, |V(G)|\}\), \(f(E(G)) = \{|V(G)| + 1, |V(G)| + 2, \ldots, |V(G)| + |E(G)|\}\). R. M. Figueroa-Centeno et al. provided the following conjecture: For every integer \(n \geq 5\), the book \(B_n\) is super edge-magic if and only if \(n\) is even or \(n \equiv 5 \pmod 8\). In this paper, we show that \(B_n\) is super edge-magic for even \(n \geq 6\).

It was conjectured in \([10]\) that the upper bound for the strong chromatic index \(s'(G)\) of bipartite graphs is \(\Delta(G)^2+1\), where \(\Delta(G)\) is the largest degree of vertices in \(G\). In this note we study the strong edge coloring of some classes of bipartite graphs that belong to the class of partial cubes. We introduce the concept of \(\Theta\)-graph \(\Theta(G)\) of a partial cube \(G\), and show that \(s'(G) \leq \chi(\Theta(G))\) for every tree-like partial cube \(G\). As an application of this bound we derive that \(s'(G) \leq 2\Delta(G)\) if \(G\) is a \(p\)-expansion graph.

We introduce notions of \(k\)-chromatic uniqueness and \(k\)-chromatic equivalence in the class of all Sperner hypergraphs. They generalize the chromatic uniqueness and equivalence defined in the class of all graphs \([10]\) and hypergraphs \([2, 4, 8]\). Using some known facts, concerning a \(k\)-chromatic polynomial of a hypergraph \([5]\), a set of hypergraphs whose elements are \(3\)-chromatically unique is indicated. A set of hypergraphs characterized by a described \(3\)-chromatic polynomial is also shown. The application of the investigated notions can be found in \([5]\).

A graph-pair of order \(t\) is two non-isomorphic graphs \(G\) and \(H\) on \(t\) non-isolated vertices for which \(G \cup H \cong K_t\) for some integer \(t \geq 4\). Given a graph-pair \((G, H)\), we say \((G, H)\) divides some graph \(K\) if the edges of \(K\) can be partitioned into copies of \(G\) and \(H\) with at least one copy of \(G\) and at least one copy of \(H\). We will refer to this partition as a \((G, H)\)-multidecomposition of \(K\).

Let \(V\) denote the \(n\)-dimensional row vector space over a finite field \(\mathbb{F}_q\), and let \(W\) be a subspace of dimension \(n-d\). Let \(L(n,d) = \mathcal{P} \cup \{0\}\), where \({P} = \{A | A \text{ is a subspace of } V, A + W = V\}\). Partially ordered by ordinary or reverse inclusion, two families of finite atomic lattices are obtained. This article discusses their geometricity, and computes their characteristic polynomials.

A graph \(G\) is called \(H\)-equipackable if every maximal \(H\)-packing in \(G\) is also a maximum \(H\)-packing in \(G\). All \(M_2\)-equipackable graphs and \(P_3\)-equipackable graphs have been characterized. In this paper, \(P_k\)-equipackable paths, \(P_k\)-equipackable cycles, \(M_3\)-equipackable paths and \(M_3\)-equipackable cycles are characterized.

Let \(G\) be a graph with \(r\) vertices of degree at least two. Let \(H\) be any graph. Consider \(r\) copies of \(H\). Then \(G \oplus H\) denotes the graph obtained by merging the chosen vertex of each copy of \(H\) with every vertex of degree at least two of \(G\). Let \(T_0\) and \(T^{A_1}\) be any two caterpillars. Define the first attachment tree \(T_1 = T_0 \oplus T^{A_1}\). For \(i \geq 2\), define recursively the \((i^{th})\) attachment tree \(T_i = T_{i-1} \oplus T^{A_i}\), where \(T_{i-1}\) is the \((i-1)^{th}\) attachment tree. Here one of the penultimate vertices of \(T^{A_1}\), \(i \geq 1\) is chosen for merging with the vertices of degree at least two of \(T_{i-1}\), for \(i \geq 1\). In this paper, we prove that for every \(i \geq 1\), the \(i\)th attachment tree \(T_i\) is graceful and admits a \(\beta\)-valuation. Thus it follows that the famous graceful tree conjecture is true for this infinite class of \((i^{th})\) attachment trees \(T’_is\), for all \(i \geq 1\). Due to the results of Rosa \([21]\) and El-Zanati et al. \([5]\) the complete graphs \(K_{2cm+1}\) and complete bipartite graphs \(K_{qm,pm}\), for \(c,p,m,q \geq 1\) can be decomposed into copies of \(i\)th attachment tree \(T_i\), for all \(i \geq 1\), where \(m\) is the size of such \(i\)th attachment tree \(T_i\).

A packing of \(K_n\) with copies of \(C_4\) (the cycle of length \(4\)), is an ordered triple \((V, \mathcal{C}, L)\), where \(V\) is the vertex set of the complete graph \(K_n\), \(C\) is a collection of edge-disjoint copies of \(C_4\), and \(L\) is the set of edges not belonging to a block of \(\mathcal{C}\). The number \(n\) is called the order of the packing and the set of unused edges \(L\) is called the leave. If \(C\) is as large as possible, then \((V, \mathcal{C}, L)\) is called a maximum packing MPC\((n, 4, 1)\). We say that an handcuffed design \(H(v, k, 1)\) \((W, P)\) is embedded into an MPC\((n, 4, 1)\) \((V, C, L)\) if \(W \subseteq V\) and there is an injective mapping \(f : \mathcal{P} \to \mathcal{C}\) such that \(P\) is a subgraph of \(f(P)\) for every \(P \in \mathcal{P}\). Let \(\mathcal{SH}(n, 4, k)\) denote the set of the integers \(v\) such that there exists an MPC\((n, 4, 1)\) which embeds an \(H(v, k, 1)\). If \(n \equiv 1 \pmod 8\) then an MPC\((n, 4, 1)\) coincides with a \(4\)-cycle system of order \(n\) and \(\mathcal{SH}(n, 4, k)\) is found by Milici and Quattrocchi, Discrete Math., \(174 (1997)\).

The aim of the present paper is to determine \(\mathcal{SH}(n, 4, k)\) for every integer \(n \not\equiv 1 \pmod 8\), \(n \geq 4\).

Given a sequence \(X = (x_1, x_2, \ldots, x_k)\), let \(Y = (y_1, y_2, \ldots, y_k)\) be a sequence obtained by rearranging the terms of \(X\). The total self-variation of \(Y\) relative to \(X\) is \(\zeta_X(Y) = \sum_{i=1}^k |y_i – x_i|\). On the other hand, let \(G = (V, E)\) be a connected graph and \(\phi\) be a permutation of \(V\). The total relative displacement of \(\phi\) is \(\delta_\phi(G) = \sum_{\{x \neq y\}\subset V} |d(x, y) – d(\phi(x), \phi(y))|\), where \(d(v, w)\) means the distance between \(v\) and \(w\) in \(G\). It’s clear that the total relative displacement of \(\phi\) is a total self-variation relative to the distance sequence of the graph.
In this paper, we determine the sequences which attain the maximum value of the total self-variation of all possible rearrangements \(Y\) relative to \(X\). Applying this result to the distance sequence of a graph, we find a best possible upper bound for the total relative displacement of a graph.

Let \(G\) be a simple undirected graph. Denote by \(mi(G)\) the number of maximal independent sets in \(G\). In this paper, we determine the second and third largest number of maximal independent sets in trees. Extremal trees achieving these values are also determined.

In \([5]\), the first author posed the problem of determining the spectrum of \((K_4, K_4 – e)\)-designs. In this article, we solve this problem, and also determine the spectrum of \((K_4, K_4 – e)\)-designs with exactly one \(K_4\) (or, equivalently, the spectrum of \((K_4 – e)\)-designs with a hole of size \(4\)). We also improve the bound for embedding a partial \(S(2,4,v)\) into a \((K_4, K_4 – e)\)-design given in \([5]\).

Given a digraph \(D\), its competition graph \(C(D)\) has the same vertex set as \(D\) and an edge between two vertices \(x\) and \(y\) if there is a vertex \(u\) so that \((x,u)\) and \((y,u)\) are arcs of \(D\). Motivated by a problem of communications, Kim and Roberts [2002] studied the competition graphs of the special digraphs known as semiorders and the graphs arising as competition graphs of acyclic digraphs satisfying conditions so called \(C(p)\) or \(C^*(p)\). While they could completely characterize the competition graph of an acyclic digraph satisfying \(C(p)\), they obtained only partial results on \(C^*(p)\) and left the general case open. In this paper, we answer their open question.

A graph \(G\) is said to be well-covered if every maximal independent set of \(G\) is of the same size. It has been shown that characterizing well-covered graphs is a co-NP-complete problem. In an effort to characterize some of these graphs, different subclasses of well-covered graphs have been studied. In this paper, we will introduce the subclass of stable well-covered graphs, which are well-covered graphs that remain well-covered with the addition of any edge. Some properties of stable well-covered graphs are given. In addition, the relationships between stable well-covered graphs and some other subclasses of well-covered graphs, including the surprising equivalence between stable well-covered graphs and other known subclasses, are proved.

Let \(G\) be a graph with vertex set \(V(G)\). For any \(S \subseteq V(G)\), we use \(w(G – S)\) to denote the number of components of \(G – S\). The toughness of \(G\), \(t(G)\), is defined as \(t(G) = \min\left\{\frac{|S|}{w(G – S)} \mid S \subseteq V(G), w(G – S) > 1\right\}\) if \(G\) is not complete; otherwise, set \(t(G) = +\infty\). In this paper, we consider the relationship between the toughness and the existence of fractional \((g, f)\)-factors. It is proved that a graph \(G\) has a fractional \((g, f)\)-factor if \(t(G) \geq \frac{b^2 – 1}{a}\).

An almost-bipartite graph is a non-bipartite graph with the property that the removal of a particular single edge renders the graph bipartite. A graph labeling of an almost-bipartite graph \(G\) with \(n\) edges that yields cyclic \(G\)-decompositions of the complete graph \(K_{2nt+1}\) (i.e., cyclic \((K_{2nt+1}, G)\)-designs) was recently introduced by Blinco, El-Zanati, and Vanden Eynden. They called such a labeling a \(\gamma\)-labeling. Here we show that the class of almost-bipartite graphs obtained from \(C_m\) by adding an edge joining distinct vertices in the same part in the bipartition of \(V(C_{2m})\) has a \(\gamma\)-labeling if and only if \(m \geq 3\). This, along with results of Blinco and of Froncek, shows that if \(G\) is a graph of size \(n\) consisting of a cycle with a chord, then there exists a cyclic \((K_{2nt+1},G)\)-design for every positive integer \(t\).

For a given graph \(H\), a graphic sequence \(\pi = (d_1, d_2, \ldots, d_n)\) is said to be potentially \(H\)-graphic if there is a realization of \(\pi\) containing \(H\) as a subgraph. In this paper, we characterize potentially \(K_{1,1,6}\)-positive graphic sequences. This characterization implies the value of \(\sigma(K_{1,1,6}, n)\). Moreover, we also give a simple sufficient condition for a positive graphic sequence \(\pi = (d_1, d_2, \ldots, d_n)\) to be potentially \(K_{1,1,s}\)-graphic for \(n \geq s+2\) and \(s \geq 2\).

Let \(H(B)\) denote the space of all holomorphic functions on the unit ball \(B\). Let \(u \in H(B)\) and \(\varphi\) be a holomorphic self-map of \(B\). This paper characterizes the boundedness and compactness of the weighted composition operator \(uC_{\varphi}\), from Bloch-type spaces to weighted-type spaces in the unit ball.

Let \(G\) be a graph of order \(n\). Let \(a\) and \(b\) be integers with \(1 \leq a < b\), and let \(k \geq 2\) be a positive integer not larger than the independence number of \(G\). Let \(g(x)\) and \(f(x)\) be two non-negative integer-valued functions defined on \(V(G)\) such that \(a \leq g(x) \frac{(a+b)(k(a+b)-2)}{a+1}\) and \(|N_G(x_1) \cup N_G(x_2) \cup \cdots \cup N_G(x_k)| \geq \frac{(b-1)n}{a+b}\) for any independent subset \(\{x_1, x_2, \ldots, x_k\}\) of \(V(G)\). Furthermore, we show that the result is best possible in some sense.

A graph \(G\) is called quasi-claw-free if it satisfies the property:\(d(x,y) = 2 \Rightarrow \text{there exists} u \in N(x) \cap N(y) \text{ such that } N[u] \subseteq N[x] \cup N[y].\) It is shown that a Hamiltonian cycle can be found in polynomial time in four subfamilies of quasi-claw-free graphs.

We study near hexagons which satisfy the following properties:(i) every two points at distance 2 from each other are contained in a unique quad of order \((s,r_1)\) or \((s,r_2), r_1\neq r_2\); (ii) every line is contained in the same number of quads; (iii) every two opposite points are connected by the same number of geodesics. We show that there exists an association scheme on the point set of such a near hexagon and calculate the intersection numbers. We also show how the eigenvalues of the collinearity matrix and their corresponding multiplicities can be calculated. The fact that all multiplicities and intersection numbers are nonnegative integers gives restrictions on the parameters of the near hexagon. We apply this to the special case in which the near hexagon has big quads.

A perfect \(r\)-code in a graph is a subset of the graph’s vertices with the property that each vertex in the graph is within distance \(r\) of exactly one vertex in the subset. We determine the relationship between perfect \(r\)-codes in the lexicographic product of two simple graphs and perfect \(r\)-codes in each of the factors.

A graph \(G\) is called uniquely \(k\)-list colorable, or \(UkLC\) for short, if it admits a \(k\)-list assignment \(L\) such that \(G\) has a unique \(L\)-coloring. A graph \(G\) is said to have the property \(M(k)\) (\(M\) for Marshal Hall) if and only if it is not \(UkLC\). The \(m\)-number of a graph \(G\), denoted by \(m(G)\), is defined to be the least integer \(k\) such that \(G\) has the property \(M(k)\). After M. Mahdian and E.S. Mahmoodian characterized the \(U2LC\) graphs, M. Ghebleh and E.S. Mahmoodian characterized the \(U3LC\) graphs for complete multipartite graphs except for nine graphs in 2001. Recently, W. He et al. verified all the nine graphs are not \(U3LC\) graphs. Namely, the \(U3LC\) complete multipartite graphs are completely characterized. In this paper, complete multipartite graphs whose \(m\)-number are equal to \(4\) are researched and the \(U4LC\) complete multipartite graphs, which have at least \(6\) parts, are characterized except for finitely many of them. At the same time, we give some results about some complete multipartite graphs whose number of parts is smaller than \(6\).

A list-assignment \(L\) to the vertices of \(G\) is an assignment of a set \(L(v)\) of colors to vertex \(v\) for every \(v \in V(G)\). An \((L,d)^*\)-coloring is a mapping \(\phi\) that assigns a color \(\phi(v) \in L(v)\) to each vertex \(v \in V(G)\) such that at most \(d\) neighbors of \(v\) receive color \(\phi(v)\). A graph is called \((k,d)^*\)-choosable, if \(G\) admits an \((L,d)^*\)-coloring for every list assignment \(L\) with \(|L(v)| \geq k\) for all \(v \in V(G)\). In this note, it is proved that:(1) every toroidal graph containing neither adjacent \(3\)-cycles nor \(5\)-cycles, is \((3,2)^*\)-choosable;(2) every toroidal graph without \(3\)-cycles, is \((3,2)^*\)-choosable.

In this note, we consider a generalized Fibonacci sequence \(\{u_n\}\). Then we give a generating matrix for the terms of sequence \(\{u_{kn}\}\) for a positive integer \(k\). With the aid of this matrix, we derive some new combinatorial identities for the sequence \(\{u_{kn}\}\).

Let \(G = (V, E)\) be a graph. A subset \(S\) of \(V\) is called a dominating set of \(G\) if every vertex in \(V – S\) is adjacent to at least one vertex in \(S\). A global dominating set is a subset \(S\) of \(V\) which is a dominating set of both \(G\) as well as its complement \(\overline{G}\). The domination number (global domination number) \(\gamma(\gamma_g)\) of \(G\) is the minimum cardinality of a dominating set (global dominating set) of \(G\). In this paper, we obtain a characterization of bipartite graphs with \(\gamma_g = \gamma + 1\). We also characterize unicyclic graphs and bipartite graphs with \(\gamma_g = \alpha_0(G) + 1\), where \(\alpha_0(G)\) is the vertex covering number of \(G\).

In paper \([7]\), S. J. Xu and W. Jin proved that a cyclic group of order \(pq\), for two different odd primes \(p\) and \(q\), is a \(3\)-BCI-group, and a finite \(p\)-group is a weak \((p – 1)\)-BCI-group. As a continuation of their works, in this paper, we prove that a cyclic group of order \(2p\) is a \(3\)-BCI-group, and a finite \(p\)-group is a \((p – 1)\)-BCI-group.

Fifty-five new or improved lower bounds for \(A(n, d, w)\), the maximum possible number of binary vectors of length \(n\), weight \(w\), and pairwise Hamming distance no less than \(d\), are presented.

We give some estimates of the norm of weighted composition operators from \(\alpha\)-Bloch spaces to Bloch-type spaces on the unit ball in \(7\).

Let \(G\) be a graph with vertex set \(V(G)\) and edge set \(E(G)\). The isolated toughness of \(G\) is defined as
\(I(G) = \min\left\{\frac{|S|}{i(G-S)}: S \subseteq V(G), i(G-S) \geq 2\right\}\)
if \(G\) is not complete. Otherwise, set \(I(G) = |V(G)| – 1\). Let \(a\) and \(b\) be positive integers such that \(1 \leq a \leq b\), and let \(g(x)\) and \(f(x)\) be positive integral-valued functions defined on \(V(G)\) such that \(a \leq g(x) \leq f(x) \leq b\). Let \(h(e) \in [0,1]\) be a function defined on \(E(G)\), and let \(d(x) = \sum_{e \in E_x} h(e)\) where \(E_x = \{xy : y \in V(G)\}\). Then \(d(x)\) is called the fractional degree of \(x\) in \(G\). We call \(h\) an indicator function if \(g(x) \leq d(x) \leq f(x)\) holds for each \(x \in V(G)\). Let \(E^h = \{e : e \in E(G), h(e) \neq 0\}\) and let \(G_h\) be a spanning subgraph of \(G\) such that \(E(G_h) = E^h\). We call \(G_h\) a fractional \((g,f)\)-factor. The main results in this paper are to present some sufficient conditions about isolated toughness for the existence of fractional \((g,f)\)-factors. If \(1 = g(x) < f(x) = b\), this condition can be improved and the improved bound is not only sharp but also a necessary and sufficient condition for a graph to have a fractional \([1,b]\)-factor.

Let \((G,C)\) be an edge-colored bipartite graph with bi-partition \((X,Y)\). A heterochromatic matching of \(G\) is such a matching in which no two edges have the same color. Let \(N^c(S)\) denote a maximum color neighborhood of \(S \subseteq V(G)\).

The spanning tree packing number of a connected graph \(G\), denoted by \(\tau(G)\), is the maximum number of edge-disjoint spanning trees of \(G\). In this paper, we determine the minimum number of edges that must be added to \(G\) so that the resulting graph has spanning tree packing number at least \(k\), for a given value of \(k\).

Let \(\gamma_{\overline{E}}\) and \(\gamma_{\overline{S}}\) be the minus edge domination and minus star domination numbers of a graph, respectively, and let \(\gamma_E\), \(\beta_1\), \(\alpha_1\) be the edge domination, matching, and edge covering numbers of a graph. In this paper, we present some bounds on \(\gamma_{\overline{E}}\) and \(\gamma_{\overline{S}}\) and characterize the extremal graphs of even order \(n\) attaining the upper bound \(\frac{n}{2}\) on \(\gamma_{\overline{E}}\). We also investigate the relationships between the above parameters.

The Wiener index of a connected graph is defined as the sum of all distances between unordered pairs of vertices. We determine the unicyclic graphs of given order, cycle length and number of pendent vertices with minimum Wiener index.

In this paper, by using the generating functions of Fibonacci polynomial sequences and their partial derivatives, we work out some identities involving the Fibonacci polynomials. As their primary applications, we obtain several identities involving the Fibonacci numbers and Lucas numbers.

Fukuda and Handa \([7]\) asked whether every even partial cube \(G\) is harmonic-even. It is shown that the answer is positive if the isometric dimension of \(G\) equals its diameter which is in turn true for partial cubes with isometric dimension at most \(6\). Under an additional technical condition it is proved that an even partial cube \(G\) is harmonic-even or has two adjacent vertices whose diametrical vertices are at distance at least \(4\). Some related open problems are posed.

By means of partial fraction decomposition, the purpose of this paper is to obtain a generalization of an algebraic identity which was given by Chu in \(\textit{The Electronic J. Camb.}\), \(11(2004), \#N15\).

Let \(G\) be a graph on \(n\) vertices \(v_1, v_2, \ldots, v_n\) and let \(d(v_i)\) be the degree of the vertex \(v_i\). If \((d(v_1), d(v_2), \ldots, d(v_n))^t\) is an eigenvector of the \((0,1)\)-adjacency matrix of \(G\), then \(G\) is said to be harmonic. A semi-regular harmonic graph is the harmonic graph which has exactly two different degrees. An equi-bipartite harmonic graph is the bipartite graph \(H = (X, Y; E)\) with \(|X| = |Y|\). In this paper, we characterize the semi-regular harmonic graph and equi-bipartite harmonic graph, and the degree sequence of equi-bipartite \(3\)-harmonic graphs.

We give necessary and sufficient conditions for a resolvable \(4\)-decomposition of \(AK_n\), in the case where \(H\) is one of the 10 graphs obtained by the union of two paths of length 2, with two possible exceptions. In particular, we complete the \(4\)-star (\(\lambda\)) and \(T\) (\(\tau\)) for higher \(\lambda\) and give complete solutions for resolvable decompositions into Fish (\(4\)-\(3\)), Mulinetto (\(hx\)) and Kites (\(BSI\)). In the cases of the Fish and Mulinetto the solution is obtained \(1\)-rotationally.

We note that with only a slight modification, Su’s proof on the fragments in \(k\)-critical \(n\)-connected graphs (see J. Graph Theory \(45 (2004), 281-297\)) can imply the following more general result: every non-complete \(W\)-locally \(k\)-critical \(n\)-connected graph has \(2k + 2\) distinct fragments \(F_1, F_2, \ldots, F_{2k+2}\) such that \(F_1 \cap W, F_2 \cap W, \ldots, F_{2k+2} \cap W\) are pairwise disjoint.

A packing of a graph \(G\) is a set of edge-disjoint \(4\)-cycles in \(G\) and a maximum packing of \(G\) with \(4\)-cycles is a packing which contains the largest number of \(4\)-cycles among all packings of \(G\). In this paper, we obtain the maximum packing of certain graphs such as \(K_{2m+1} – H\) where \(H\) is a \(2\)-regular subgraph, \(K_{2m} – F\) where \(F\) is a spanning odd forest of \(K_{2m}\), and \(2K_{2m} – L\) where \(L\) is a \(2\)-regular subgraph of \(2K_{2m}\).

In this paper, we consider the relationships between the second order linear recurrences, and the generalized doubly stochastic permanents and determinants.

An \(\lambda\)-design on \(v\) points is a set of \(v\) subsets (blocks) of a \(v\)-set such that any two distinct blocks meet in exactly \(\lambda\) points and not all of the blocks have the same size. Ryser’s and Woodall’s \(\lambda\)-design conjecture states that all \(\alpha\)-designs can be obtained from symmetric designs by a complementation procedure. In a previous paper, the author established feasibility criteria for the existence of \(\lambda\)-designs with two block sizes in the form of integrality conditions, equations, inequalities, and Diophantine equations involving various parameters of the designs. In that paper, these criteria and a computer were used to prove that the \(\lambda\)-design conjecture is true for all \(\lambda\)-designs with two block sizes with \(\lambda \leq 90\) and \(\lambda \neq 45\). In this paper, we extend these results and prove that the \(\lambda\)-design conjecture is also true for all \(\lambda\)-designs with two block sizes with \(\lambda = 45\) or \(91 \leq \alpha < 150\).