Let’s define $\sigma(G)$ as the sum of orders of all normal subgroups of a finite group $G$. Do there exist two finite groups $H$ and $K$ such, that $\sigma(H) = |H| + |K| = \sigma(K)$ and $H$ is non-cyclic?
Why $H$ is required to be non-cyclic? A pair of cyclic groups $H$ and $K$ satisfies that condition iff $|H|$ and $|K|$ form an amicable pair. And it would be interesting to know, what happens if at least one of those groups is non-cyclic.
A quick MAGMA code I wrote finds the following example with $$H=D_{10} \quad , K=D_{19}$$ Indeed, in both cases
$\sigma(K)=1+19+38=58$
$\sigma(H)=1+2+5+10+10+10+20= 58$
and $|H|+|K|=20+38 =58$.
Here is the very naive and probably bugged (the $i^j$ indexing definitely doesn't work, $2^4 = 4^2$ so I am missing some examples, and it checks everything twice which is not efficient) code if you are interested. I checked for examples up to $60$.
And the output
Note that it also contains other examples that might be interesting of "self-amicable groups", such as SmallGroup(30,1) $= C_5 \times S_3$.
By self-amicable I mean that they mimic the behaviour of $28$ which forms an amicable pair with itself (realised in group theory by $C_{28}$).
Edit: found this paper https://arxiv.org/pdf/math/0104012.pdf
Edit 2: found this paper as well http://cage.ugent.be/~tdemedts/preprints/leinster.pdf