Families of Type-2 Isomorphic Circulant Graphs of Order $np^3$ w.r.t. $r = p$ and Their Abelian Groups

Vilfred Kamalappan, Wilson Peraprakash

Published 2022-11-13Version 1

Circulant graphs $C_n(R)$ and $C_n(S)$ are said to be \emph{Adam's isomorphic} if there exist some $a\in \mathbb{Z}_n^*$ such that $S = a R$ under arithmetic reflexive modulo $n$. $C_n(R)$ is said to have {\it Cayley Isomorphism} (CI)-property if whenever $C_n(S)$ is isomorphic to $C_n(R),$ they are of Adam's isomorphic. CI-problem determines which graphs (or which groups) have the $CI$-property. Classification of cyclic $CI$-groups was completed but investigation of graphs without $CI$-property is not much done. Vilfred defined Type-2 isomorphism, different from Adam's isomorphism, of circulant graphs $C_n(R)$ w.r.t. $r$, $r\in R$ $\ni$ $\gcd(n, r) = m > 1$. Type-2 isomorphic circulant graphs don't have CI-property and we obtained such graphs of order $n$ for $r$ = 2,3,5,7, $n\in\mathbb{N}$. In this paper, we obtain Type-2 isomorphic circulant graphs of order $np^3$ w.r.t. $r = p$, and abelian groups on these isomorphic graphs where $p$ is a prime number and $n\in\mathbb{N}$. Theorems \ref{c10} and \ref{c13} are the main results. Using Theorem \ref{c13}, a list of abelian groups on the $p$ isomorphic circulant graphs $C_{np^3}(R^{np^3,x+yp}_i)$ of Type-2 w.r.t. $r = p$ for $i$ = 1 to $p$ and for $p$ = 3,5,7, $n$ = 1,2 and $y$ = 0 is given in the Annexure, $1 \leq x \leq p-1$, $y\in\mathbb{N}_0$, $0 \leq y \leq np - 1$, $1 \leq x+yp \leq np^2-1$, $p,np^3-p\in R^{np^3,x+yp}_i$ and $i,n,x\in\mathbb{N}$.