\NThe symbol \N is used to denote the set of natural numbers in mathematical notation. It is a part of the category of Other Letters in LaTeX, typically represented in blackboard bold font to distinguish it from other uses of the letter 'N'.
Indicating that x is a natural number.
x \in \NDefining the set of natural numbers.
\N = \{1, 2, 3, \ldots\}A function from natural numbers to natural numbers.
f: \N \to \N