ThmDex – An index of mathematical definitions, results, and conjectures.
Set of symbols
Deduction system
Zermelo-Fraenkel set theory
Collection of sets
Set union
Successor set
Inductive set
Set of inductive sets
Set of natural numbers
Natural number
Definition D1580
Fermat number
Formulation 0
A D996: Natural number $n \in \mathbb{N}$ is a Fermat number if and only if \begin{equation} \exists \, m \in \mathbb{N} : 2^{(2^m)} + 1 = n \end{equation}