Exact 2-Distance b-Coloring and Exact 2-Distance b-Continuity of Helm Graph 𝑯𝒏

Abstract

An exact 2-distance coloring of a graph 𝐺 is a coloring of vertices of 𝐺 such that any two vertices which are at distance exactly 2 receive distinct colors. An exact 2-distance chromatic number𝑒2(𝐺) of 𝐺 is the minimum 𝑘 for which 𝐺 admits an exact 2-distance coloring with 𝑘 colors. A 𝑏-coloring of 𝐺 by 𝑘 colors is a proper 𝑘-vertex coloring such that in each color class, there exists a vertex called a color dominating vertex which has a neighbor in every other color class. A vertex that has a 2-neighbor in all other color classes is called an exact 2-distance color dominating vertex (or an 𝑒2-cdv). Exact 2-distance 𝑏-coloring (or an 𝑒2𝑏-coloring) of 𝐺 is an exact 2-distance coloring such that each color class contains an 𝑒2- cdv. An exact 2-distance 𝑏-chromatic number (or an 𝑒2𝑏-number) 𝑒2𝑏(𝐺) of 𝐺 is the largest integer 𝑘 such that 𝐺 has an 𝑒2𝑏-coloring with 𝑘colors. If for each integer𝑘, 𝑒2(𝐺) ≤ 𝑘 ≤ 𝑒2𝑏(𝐺), 𝐺 has an 𝑒2𝑏-coloring by 𝑘 colors, then 𝐺 is said to be an exact 2-distance 𝑏- continuous graph. In this paper, the 𝑒2𝑏-number𝑒2𝑏(𝐻𝑛)of the helm graph 𝐻𝑛is obtained and 𝑒2𝑏-continuity of 𝐻𝑛is discussed.