[1] BERKOVICH, YA. G.-ZHMUD E.: Characters of Finite Groups. Part 1. Transl. Math. Monographs 172, Amer. Math. Soc, Providence, RI, 1997. MR 1486039

[2] CONWAY J. H.-CURTIS R. T.-NORTON S. R-PARKER R. A.-WILSON R. A.: Atlas of Finite Groups. Clarendon Press, Oxford, 1985. MR 0827219

[3] DARAFSHEH M. R.-SHARIFI H.: Frobenius Q-groups. Arch. Math. (Basel) 83 (2004), 102-105. MR 2104937

[4] FEIT W.-SEITZ G. M.: On finite rational groups and related topics. Illinois J. Math. 33 (1988), 103-131. MR 0974014

[5] GOW R.: Groups whose characters are rational-valued. J. Algebra 40 (1976), 280-299. MR 0409620 | Zbl 0348.20017

[6] HAYASHI M.: On a generalizatгon of F. M. Markeľs Theorem. Hokaido Math. J. 4 (1975), 278-280. MR 0372001

[7] KLETZING D.: Structure and Representations of Q-Groups. Springer-Verlag, Bеrlin-Hеidеlbеrg-New York-Tokyo, 1984. MR 0765700 | Zbl 0546.20005

[8] SUZUKI M.: Group Theory, Vols. 1, 2. Springеr-Vеrlag, Bеrlin-Hеidеlbеrg-Nеw York-Tokyo, 1982. MR 0648772