Let $r(m)$ denote the residue class $r+m\mathbb{Z}$, where $0 \leq r < m$. Given disjoint residue classes $r_1(m_1)$ and $r_2(m_2)$, let the class transposition $\tau_{r_1(m_1),r_2(m_2)}$ be the permutation of $\mathbb{Z}$ which interchanges $r_1+km_1$ and $r_2+km_2$ for every $k \in \mathbb{Z}$ and which fixes everything else.

Question: Let $G < {\rm Sym}(\mathbb{Z})$ be a group generated by $3$ class transpositions, and assume that the integers $0, \dots, 42$ all lie in the same orbit under the action of $G$ on $\mathbb{Z}$. Is the action of $G$ on $\mathbb{N}_0$ necessarily transitive?

Remarks:

• When replacing $42$ by $41$, the answer obviously gets negative since the finite group $$ G \ := \ \langle \tau_{0(2),1(2)}, \tau_{0(3),2(3)}, \tau_{0(7),6(7)} \rangle $$ acts transitively on the set $\{0, \dots, 41\}$. Therefore if true, the assertion is sharp.

• There is computational evidence suggesting that there is, say, "a reasonable chance" that the answer is positive.

• A positive answer would mean that groups generated by $3$ class transpositions are "well-behaved" in the sense that for deciding transitivity, looking at very small numbers is sufficient, and that for larger numbers "nothing can happen any more".

• A positive answer would imply the Collatz conjecture. On the other hand, if the Collatz conjecture holds, this would (by far!) not imply a positive answer to the question.

• There is a related question here.