NonConstants is an option for D which gives a list of objects to be taken to depend implicitly on the differentiation variables.
NonNegative[x] gives True if x is a non-negative number.
NonPositive[x] gives True if x is a non-positive number.
Normal
(Built-in Mathematica Symbol) Normal[expr] converts expr to a normal expression, from a variety of special forms.
NormalsFunction is an option for Plot3D and related functions that specifies a function to apply to determine the effective surface normals at every point.
NormFunction is an option for functions such as FindFit and NDSolve which gives a function to be minimized in generating results.
Nor
(Built-in Mathematica Symbol) Nor[e_1, e_2, ...] is the logical NOR function. It evaluates its arguments in order, giving False immediately if any of them are True, and True if they are all False.
NotebookApply[notebook, data] writes data into a notebook at the current selection, replacing the first selection placeholder in data by the current selection, and then ...
NotebookBrowseDirectory is a global option that determines the current working directory.
NotebookClose[notebook] closes the notebook corresponding to the specified notebook object. NotebookClose[] closes the current evaluation notebook.