1. T. Andreescu, D. Andrica, Number Theory. Structures, Examples, and Problems (Birkhauser Verlag, Boston, 2009)
2. D. Andrica, M. Piticari, On some extensions of Jordan’s arithmetic functions, in Proceedings of the International Conference on Theory and Applications of Mathematics and Informatics – ICTAMI 2003, Alba Iulia, vol. 7. Acta Univ. Apulensis Math. Inform. (2004), pp. 13–22
3. D. Andrica, S. Rădulescu, G. C. Ţurcaş, On the automorphism group of direct products of groups with finite exponent, Am. Math. Mon., to appear
4. J. Belk, Finding the number of elements of particular order in the symmetric group, URL (version: 2015-06-26): https://math.stackexchange.com/q/1340368
5. E.A. Bender, J.R. Goldman, On the applications of Möbius inversion in combinatorial analysis. Am. Math. Mon. 82(8), 789–803 (1975)