Srinivasa Rao Kola, Pratima Panigrahi, Department of Mathematics, Indian Institute of Technology, Kharagpur 721302, India, e-mail: srinivas@maths.
iitkgp.ernet.in, pratima@maths.iitkgp.ernet.in
Abstract: Chartrand et al. (2004) have given an upper bound for the nearly antipodal chromatic number $ac'(P_n)$ as $\binom{n-2}2+2$ for $n \geq9$ and have found the exact value of $ac'(P_n)$ for $n=5,6,7,8$. Here we determine the exact values of $ac'(P_n)$ for $n \geq8$. They are $2p^2-6p+8$ for $n=2p$ and $2p^2-4p+6$ for $n=2p+1$. The exact value of the radio antipodal number $ac(P_n)$ for the path $P_n$ of order $n$ has been determined by Khennoufa and Togni in 2005 as $2p^2-2p+3$ for $n=2p+1$ and $2p^2-4p+5$ for $n=2p$. Although the value of $ac(P_n)$ determined there is correct, we found a mistake in the proof of the lower bound when $n=2p$ (Theorem $6$). However, we give an easy observation which proves this lower bound.
Keywords: radio $k$-coloring, span, radio $k$-chromatic number
Classification (MSC 2000): 05C78, 05C12, 05C15
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