\bibitem{BR92} R. A. Brualdi, Introductory Combinatorics, New York, North Holland, Second Edition,
1992.
\bibitem{DA81} P. S. Das, {\em Fuzzy groups and level subgroups}, J. Math. Anal. Appl., {\bf 84} (1981), 264-269.
\bibitem{JCLJ2011} S. Jia, Y. Chen, J. Liu and Y. Jiang, {\em On the number of fuzzy subgroups
of finite abelian p-groups with type $(p^n, p^m)$}, In Proceedings
of The 3rd International Conference on Computer Research and
Development, China, {\bf 4} (2011), 62-64.
\bibitem{NG05} S. Ngcibi, {\it Studies of equivalent fuzzy
subgroups of finite abelian $p$-groups of rank two and their
subgroup lattices}, Thesis, (PhD) Rhodes university, 2005.
\bibitem{NMM10} S. Ngcibi, V. Murali and B. B. Makamba, {\em Fuzzy subgroups of rank two
abelian $p$-group}, Iranian Journal of Fuzzy Systems, {\bf 7(2)} (2010),
149-153.
\bibitem{PS98} E. Pergola and R. A. Sulanke, {\em Schr\"{o}der triangles, paths, and
parallelogram polyominoes}, J. Integer Seq., Article
98.1.7., {\bf 1} (1998).
\bibitem{SL} N. J. A. Sloane, {\it The on-line encyclopedia of integer
sequences}, https://oeis.org.
\bibitem{TB08} M. T\u{a}rn\u{a}uceanu and L. Bentea, {\em On the number of fuzzy subgroups of finite abelian
groups}, Fuzzy Sets and Systems, {\bf 159} (2008), 1084-1096.
\bibitem{Tu95} A. Tucker, {\it Applied combinatorics}, John Wiley \& Sons, Inc., New York, 1995.