Muthoka Geoffrey Ngovi2025-12-162019-12https://repository.nrf.go.ke/handle/123456789/1520The concept of the cycle index formulas of a permutation group was discovered in the year 1937. Since then cycle index formulas of several groups have been studied by different scholars. For instance the cycle index of the dihedral group Dn acting on the set of vertices of a regular n−gon is known and has been applied in enumeration of different mathematical structures. In this study the relationship between the cycle index formula of a semidirect product group and the cycle index formulas of the two subgroups which the group is a semidirect product of was established. In particular the cycle index formula of the dihedral group Dn of order 2n is expressed in terms of the cycle index formula of a cyclic group of order two C2 and the cycle index formula of the cyclic group of order n, Cn; the cycle index formula of the symmetric group Sn is expressed in terms of the cycle index formula of the alternating group An and the cycle index formula of a group generated by a cycle of length two, h(ab)i. The cycle index formula of an affine(p) group has been derived by considering the different cycle types of elements of the group and expressed in terms of the cycle index formula of Cp = {x + b, where b ∈ Zp} and the cycle index formula of Cp−1 = {ax, where 0 6= a ∈ Zp}. We further extend this to affine(q) where q is a power of a prime p and to the affine square(p) and affine square(q) groups. Finally, the cycle index formula of a Frobenius group is expressed in terms of the cycle index formula of the Frobenius complement H and the cycle index formula of the Frobenius kernel M. The cycle index formulas which are known such as that of the dihedral group and the symmetric group were used and the groups whose cycle index formulas are not known such as the affine(p), affine square(p), affine(q) and affine square(q) group were first derived as part of the research. It was noted that for semidirect groups which are Frobenius such as the dihedral group Dn with an odd value of n, the affine groups and the affine square groups, we can fully express the cycle index of the group in terms of the cycle index formulas of the subgroups which the group is a semidirect of. However, for semidirect product groups which are not Frobenius such as the dihedral group Dn with an even value of n and the symmetric group Sn, the cycle index formula of the group cannot be expressed fully in terms of the cycle index formulas of the subgroups the group is a semidirect product of.enThesis