Order-Divisor Graphs of \(\Gamma_1\)-Nonderanged Permutation Groups: Structure and Invariants
Sulaiman Dauda *
Department of Mathematics, Abdullahi Fodio University of Science and Technology, Aliero, Kebbi State, Nigeria.
Anas Yusuf
Department of Mathematics, Federal University, Birnin Kebbi, Kebbi State, Nigeria.
Aminu Alhaji Ibrahim
Department of Mathematics, Usmanu Danfodiyo University, Sokoto, Sokoto State, Nigeria.
Abor Isa Garba
Department of Mathematics, Usmanu Danfodiyo University, Sokoto, Sokoto State, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
For each prime \(p \geq 5\), the \(\Gamma_1\)-nonderanged permutation group \(G_p^{\Gamma_1}=\left\{\omega_1, \ldots, \omega_{p-1}\right\}\), with multiplication \(\omega_i \omega_j=\omega_{i j \bmod p}\), is cyclic of order \(n=p-1\). Its order-divisor graph has the group elements as vertices, with distinct vertices adjacent precisely when their orders differ and one order divides the other. In view of the established divisor-class construction for cyclic groups, this graph is an independent-set expansion of the divisibility-comparability graph on the divisors of \(n\). We express this description in the permutation indexing, obtain formulas for the degrees and number of edges, and determine connectivity, regularity, diameter, radius, girth, center, and periphery. In particular, the identity is always universal; the unique involution is also universal exactly when \(p-1\) is a power of 2 . The graph is complete multipartite precisely when \(p-1=2^k(k \geq 2)\) or \(p-1=2 q\) for an odd prime \(q\). Explicit matrices and graph drawings for \(p=5,7,11\), together with direct enumeration for all 107 primes \(5 \leq p<600\), illustrate and check the specializations.
Keywords: Order-divisor graph, cyclic group, divisor comparability, eccentricity, center, complete multipartite graph, \(\Gamma_1\)-nonderanged permutation group