On edge irregularity strength of cycle-star graphs
For a simple graph $G$, a vertex labeling $ϕ:V(G) \rightarrow \{1, 2,\ldots,k\}$ is called $k$-labeling. The weight of an edge $uv$ in $G$, written $w_ϕ(uv)$, is the sum of the labels of end vertices $u$ and $v$, i.e., $w_ϕ(uv)=ϕ(u)+ϕ(v)$. A vertex $k$-labeling is defined to be an edge irregular $k$-labeling of the graph $G$ if for every two distinct edges $u$ and $v$, $w_ϕ(u) \neq w_ϕ(v)$. The minimum $k$ for which the graph $G$ has an edge irregular $k$-labeling is called the edge irregularity strength of $G$, written $es(G)$. In this paper, we study the edge irregular $k$-labeling for cycle-star graph $CS_{k,n-k}$ and determine the exact value for cycle-star graph for $3 \leq k \leq 7$ and $n-k \geq 1$. Finally, we make a conjecture for the edge irregularity strength of $CS_{k,n-k}$ for $k \geq 8$ and $n-k \geq 1$.