A noncototient is a positive integer 
for which 
has no positive integer
solution 
, where 
is the totient function.
The first few are 10, 26, 34, 50, 52, ... (OEIS A005278).
Noncototient
See also
Nontotient, Totient FunctionExplore with Wolfram|Alpha
References
Guy, R. K. Unsolved Problems in Number Theory, 2nd ed. New York: Springer-Verlag, p. 91, 1994.Sloane, N. J. A. Sequence A005278/M4688 in "The On-Line Encyclopedia of Integer Sequences."Referenced on Wolfram|Alpha
NoncototientCite this as:
Weisstein, Eric W. "Noncototient." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Noncototient.html