@article{10_1007_s10587_014_0135_4,
     author = {Shao, Changguo and Jiang, Qinhui},
     title = {Finite groups whose set of numbers of subgroups of possible order has exactly 2 elements},
     journal = {Czechoslovak Mathematical Journal},
     pages = {827--831},
     publisher = {mathdoc},
     volume = {64},
     number = {3},
     year = {2014},
     doi = {10.1007/s10587-014-0135-4},
     mrnumber = {3298563},
     zbl = {06391528},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.1007/s10587-014-0135-4/}
}