Nontotient
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).
References
Guy, R. K. Unsolved Problems in Number Theory, 2nd ed. New York: Springer-Verlag, p. 91, 1994. Sloane, N. J. A. SequenceA005277/M4927in ``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.
- Mean
- Mean Cluster Count Per Site
- Mean Cluster Density
- Mean Curvature
- Mean Deviation
- Mean Distribution
- Mean Run Count Per Site
- Mean Run Density
- Mean Square Error
- Mean-Value Theorem
- Measurable Function
- Measurable Set
- Measurable Space
- Measure
- Measure Algebra
- Measure Polytope
- Measure-Preserving Transformation
- Measure Space
- Measure Theory
- Mechanical Quadrature
- Mecon
- Medial Axis
- Medial Deltoidal Hexecontahedron
- Medial Disdyakis Triacontahedron
- Medial Hexagonal Hexecontahedron