Define a group to be 2-locally finite if, for any two elements, the subgroup generated by them is finite.

Define a group to be locally finite if the subgroup generated by any finite subset is finite.

I want an example of a 2-locally finite group that is not locally finite.

This paper https://arxiv.org/pdf/1403.0331.pdf discusses a special case where 2-locally finite groups must be locally finite (namely, the case of groups with a planar lattice of subgroups).

More generally: for a nonnegative integer n, call a group n-locally finite if every subset of size at most n generates a finite group.

I'm interested more generally in examples of n-locally finite groups that are not (n + 1)-locally finite. Currently I know of solutions for:

- n = 0: This is trivial; any group that has elements of infinite order will do.
- n = 1: This means a periodic group (every element has finite order) where there is an infinite subgroup generated by two elements. Examples here include the Grigorchuk group and some negative solutions to the Burnside problem (specifically, things like Tarski monsters); I've compiled this info at https://groupprops.subwiki.org/wiki/Periodic_not_implies_locally_finite