A Positive Even value of for which , where is the Totient Function, has no solution. The first few are 14, 26, 34, 38, 50, ... (Sloane's A005277).
See also Noncototient, Totient Function
References
Guy, R. K. Unsolved Problems in Number Theory, 2nd ed. New York: Springer-Verlag, p. 91, 1994.
Sloane, N. J. A. Sequence
A005277/M4927
in ``An On-Line Version of the Encyclopedia of Integer Sequences.''
http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.
The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.