Iranian Mathematical Society (IMS)Bulletin of the Iranian Mathematical Society1017-060X39520131015Some combinatorial aspects of finite Hamiltonian groups841854446ENM.TarnauceanuFaculty of Mathematics, "Al. I. Cuza" UniversityJournal Article20110903In this paper we provide explicit formulas for the number of elements/subgroups/cyclic subgroups of a given order and for the total number of subgroups/cyclic subgroups in a finite Hamiltonian group. The coverings with three proper subgroups and the principal series of such a group are also counted. Finally, we give a complete description of the lattice of characteristic subgroups of a finite Hamiltonian group.http://bims.iranjournals.ir/article_446_709d30bd2ac8176682140ee62d6a4254.pdf