We give a lower bound for the Ramsey number and the planar Ramsey number for C4 and complete graphs. We prove that the Ramsey number for C4 and K7 is 21 or 22. Moreover we prove that the planarâ€¦ (More)

The planar Ramsey number PR(G;H) is the smallest integer n such that in any two-colouring (red and blue) of edges of Kn such that the red colour induces a planar graph there is a red subgraph G or aâ€¦ (More)

We study the problem of the location of real zeros of chromatic polynomials for some families of graphs. In particular, a problem presented byThomassen (see [On the number of hamiltonian cycles inâ€¦ (More)

Let H = (V (H), E(H)) be a simple connected graph of order n with the vertex set V (H) and the edge set E(H). We consider a blow-up graph G[H ]. We are interested in the following problem. We have toâ€¦ (More)

We define some infinite subfamily of hexagonal grids with the oriented chromatic number 5. We present an algorithm for oriented colouring of some hexagonal planar oriented grids. The algorithm usesâ€¦ (More)

We give the multicolor Ramsey number for some graphs with a path or a cycle in the given sequence, generalizing a results of Faudree and Schelp [4], and Dzido, Kubale and Piwakowski [2, 3].