Erdős, P. "Some Remarks on Euler's -Function." Acta Arith.4, 10-19, 1958.Ford, K. "The Distribution of Totients." Ramanujan J.2, 67-151, 1998a.Ford, K. "The Distribution of Totients, Electron. Res. Announc. Amer. Math. Soc.4, 27-34, 1998b.Guy, R. K. Unsolved Problems in Number Theory, 2nd ed. New York: Springer-Verlag, p. 94, 1994.Schlafly, A. and Wagon, S. "Carmichael's Conjecture on the Euler Function is Valid Below ." Math. Comput.63, 415-419, 1994.Schinzel, A. "Sur l'equation " Elem. Math.11, 75-78, 1956.