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Let $n=3^m$ for some positive integer $m$. Let $G\leq S_n$ be a transitive permutation group on $n$ letters. Denote the largest normal subgroup of $G$ with odd order by $O_{2'}(G)$. My question is the following:

Does there exist $G$ such that $G/O_{2'}(G)\cong A_4$ or $S_4$ for suitable $m$?

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  • $\begingroup$ @verret Thanks for your comment. I will try it along this way. $\endgroup$ Commented Jul 5, 2021 at 7:00

2 Answers 2

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Let $\Omega=\{1,2,3,4,5,6,7,8,9\}$ and let $G\leq\mathrm{Sym}(\Omega)$ be the group generated by the following permutations:

  • $(1, 2, 9)$
  • $(4, 5)(7, 8)$
  • $(1, 4, 7)(2, 5, 8)(3, 6, 9)$
  • $(3, 6)(4, 7)(5, 8)$

This is an example with $n=9$, with $G/O_{2'}\cong S_4$. If you want $G/O_{2'}\cong A_4$, remove the last generator.

To get larger examples, we can simply use direct products: let $H$ be a group of odd order acting transitively on $\Omega'$, with $|\Omega'|=3^{m-2}$ (for example, an elementary abelian $3$-group acting regularly). We can view $G\times H$ as a permutation group on $\Omega\times\Omega'$ with coordinate wise action, and it has the required properties.

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  • $\begingroup$ Thanks for your useful answer. $\endgroup$ Commented Jul 5, 2021 at 6:54
  • $\begingroup$ @varret There may be some mistake in your example. When m=2, the group you constructed is of order 72, and it's not difficult to show that $O_2(G)=1, O_3(G)=N$. $\endgroup$ Commented Jul 6, 2021 at 8:30
  • $\begingroup$ @varret We must have $C_G(N)\leq N$ since $N=F(G)$ and $G$ is solvable. But this is impossible. $\endgroup$ Commented Jul 6, 2021 at 8:32
  • $\begingroup$ I fixe the construction. $\endgroup$
    – verret
    Commented Jul 7, 2021 at 1:11
  • $\begingroup$ @varret Thanks. $\endgroup$ Commented Jul 7, 2021 at 1:38
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This answers the first, unedited, version of the question. I leave it because the question may be edited again. If you take $G=S_4$ then 1)$G/O_{2'}(G)=S_4$ and 2) $G$ is inside $S_9$ and any $S_{3^m}$ for $m>1$.

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  • $\begingroup$ @GHfromMO: My answer and the edited version of the question appeared at exactly the same time (within a few seconds of each other). Then I modified the answer. $\endgroup$
    – markvs
    Commented Jul 5, 2021 at 6:25
  • $\begingroup$ @MarkSapir: I see. Let's delete these comments then (as obsolete and irrelevant). $\endgroup$
    – GH from MO
    Commented Jul 5, 2021 at 20:08

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