1. G. Bhowmik and H. Menzer, “On the number of subgroups of finite Abelian groups,” Abh. Math. Sem. Univ. Hamburg, bf67, 117–121 (1997).
2. G. Bhowmik and J. Wu, “On the asymptotic behaviour of number of subgroups of finite abelian groups,” Archiv der Math., 69, 95–104 (1997).
3. M. E. Changa, Method of Complex Integration, Steklov Math. Inst. of the RAS, Moscow, 2006.
4. N. Fugelo and I. Velichko, “Average orders of divisor function of integer matrices in $ {M_3}\left( \mathbb{Z} \right) $ ,” Annal. Univ. Sci. Budapest, Sect. Comp., 28, 261–271 (2008).
5. A. Ivič, The Riemann Zeta-Function, Wiley, New York, 1985.