Rationally powered group

Definition

A group $G$ is termed rationally powered or uniquely divisible if it satisfies the following equivalent conditions:

1. For every $u\in G$ and every natural number $n$, there is a unique $v\in G$ such that $v^n=u$.
2. $G$ is a powered group for all prime numbers.
3. For any integers $m,n$ with $n\ne 0$, and for any $g\in G$, there exists a unique $h\in G$ such that $g^m=h^n$.

More generally, we can talk of a powered group for a set of primes.

This article defines a group property: a property that can be evaluated to true/false for any given group, invariant under isomorphism
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VIEW RELATED: Group property implications | Group property non-implications |Group metaproperty satisfactions | Group metaproperty dissatisfactions | Group property satisfactions | Group property dissatisfactions

Relation with other properties

Weaker properties

Property	Meaning	Proof of implication	Proof of strictness (reverse implication failure)	Intermediate notions
torsion-free group	no non-identity element of finite order	obvious	the group of integers is torsion-free but not rationally powered.	|FULL LIST, MORE INFO
divisible group	every element has at least one $n^{th}$ root for every $n$	obvious (rationally powered additionally guarantees uniqueness)	the group of rational numbers modulo integers	|FULL LIST, MORE INFO
powering-injective group	no two different elements can have the same $n^{th}$ power.	obvious	the group of integers is powering-injective but not rationally powered.	|FULL LIST, MORE INFO

Facts

• A nilpotent group is rationally powered iff it is divisible and torsion-free. This follows from the more general fact that in a nilpotent torsion-free group, if roots exist, they are unique.