@article{SF_1980__21_134455,
     author = {K. Todorov},
     title = {On the orders of the subsemigroups of the symmetrical semigroup {Jn.}},
     journal = {Semigroup forum},
     pages = {329--336},
     publisher = {mathdoc},
     volume = {21},
     year = {1980},
     zbl = {0458.20059},
     url = {http://geodesic.mathdoc.fr/item/SF_1980__21_134455/}
}