1. The symmetric group of degree six can be covered by 13 and no fewer proper subgroups;Abdollahi;Bull. Malays. Math. Sci. Soc. (2),2007
2. Groups which are the union of three subgroups;Bruckheimer;Amer. Math. Monthly,1970
3. Subgroup coverings of some linear groups;Bryce;Bull. Austral. Math. Soc.,1999
4. On n-sum groups;Cohn;Math. Scand.,1994
5. On the structure of primitive n-sum groups;Detomi;Cubo,2008