Definition:Noncototient

Definition
A noncototient is a positive integer $n$ such that:
 * $\nexists m \in \Z_{>0}: m - \map \phi m = n$

where $\map \phi m$ denotes the Euler $\phi$ function.

That is, a noncototient is a positive integer which is not the cototient of any positive integer.

Also see

 * Definition:Cototient