# What's the smallest non-$p$ group that isn't a semidirect product?

Although every non-simple group can be described as a group extension, it is well-known that not every non-simple group can be expressed as a semidirect product of smaller groups.

For example, a cyclic group of order $$p^2$$ is an extension of $$\mathbb{Z}_p$$ by $$\mathbb{Z}_p$$, but cannot be written as a semidirect product. The quaternion group $$Q_8$$ is also not a semidirect product. Indeed, this seems to be very common property for $$p$$-groups.

So my question is:

What's the smallest non-simple group $$G$$ such that:

• $$G$$ isn't a $$p$$-group, and

• $$G$$ can't be expressed as a semidirect product of smaller groups?

What about $\mathtt{SmallGroup}(48,28)$, which is a group that is similar to ${\rm GL}(2,3)$ but has no non-central elements of order $2$? It is one of the two Schur covering groups $2 \cdot S_4$ of $S_4$ (the other one being ${\rm GL}(2,3)$).
• @zibadawatimmy Yes, it is an answer to the question. I was politely disputing the claim that ${\rm SL}(2,5)$ is the correct answer! Sorry to be confusing! – Derek Holt Jun 22 '15 at 9:21