REFERENCES
- Amiri , H. , Jafarian Amiri , S. M. , Isaacs , I. M. ( 2009 ). Sums of element orders in finite groups . Comm. Algebra 37 ( 9 ): 2978 – 2980 .
- Isaacs , I. M. ( 2008 ). Finite Group Theory . Providence , R. I. : Amer. Math. Soc .
- Wilson , L. ( 2002 ). On the power structure of powerful p-groups . J. Group Theory 5 : 129 – 144 .
- Communicated by A. Turull.