Let $G$ be a finite group ( some finite representation is given ) and Let $N$ be a normal subgroup of group $G$. I know that given a $N$ and $G/N$ one can't get back a $G$ ( always ). My question is opposite given a $G$, Is it possible to find a $N$ which is a normal subgroup of $G$ ( suppose there always exists a normal subgroup $N$ in $G$) such that one can get back $G$ from $G/N$ and $N$ only?
Please note that $N$ should be non-trivial and $G$ is indecomposable means we can't write $G$ as a direct product of non-trivial subgroups.
As pointed out by Don Sir, you can write it in trivial way..
but in general if group is abelian then by fundamental theorem of finite abelian group you can decompose that into product of normal.
to give example see.
$G=Z_{49}$ Now $Z_7$ is only possible normal subgroup ofcourse nontrivial then you get that $Z_7\times Z_7$ , which are not isomorphic to original group,
Some groups can be decomposed using semidirect product..
Example $D_n$ in that A= is normal group. B=< s > ,
$D_n\cong A\rtimes B$