# Classification of finite 2-groups of maximal class

This article gives a classification statement for certain kinds of groups of prime power order, subject to additional constraints.
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## Statement

Let $G$ be a group of order $2^n$ and nilpotency class $n - 1$, where $n \ge 4$. In other words, $G$ is a 2-group that is also a Maximal class group (?). Then, $G$ has a cyclic maximal subgroup $M \cong \mathbb{Z}/2^{n-1}\mathbb{Z}$, and it is one of the following groups:

1. A dihedral group: it is a semidirect product of $M$ and a cyclic group of order two, which acts on $M$ via multiplication by -1.
2. A semidihedral group: a semidirect product of $M$ and a cyclic group of order two, which acts on $M$ via multiplication by $2^{n-2} - 1$.
3. A generalized quaternion group.

Note that in the case $n = 3$, we only get the dihedral group:D8 and the quaternion group, and no semidihedral group.