Let $R$ and $R'$ be rings (with 1 but no further assumptions) and $n \in \mathbb{N}$. Does the following implication hold?
If $M_n(R) \simeq M_n(R')$ then $R \simeq R'$.
If the rings are commutative then it follows from considering the centers of $M_n(R)$ and $M_n(R')$. If the rings are division it also holds and even stronger, it holds even if the matrices are not of the same size.
I thought about considering the embeddings of $R$ in $M_n(R)$ as diagonal matrices, but since I do not want to asume anything about the isomorphism I was not able to conclude that these subrings of matrices in $M_n(R)$ and $M_n(R')$ are isomorphic. I hope someone can help me or with a proof, an idea or a counterexample. Thank you.
There are counterexamples.
I'm not sure how easy the simplest examples are, but you could look at
Chatters, A. W., Non-isomorphic rings with isomorphic matrix rings, Proc. Edinb. Math. Soc., II. Ser. 36, No. 2, 339-348 (1993). ZBL0796.16022.
which has examples (not the first), and whose introduction gives a good overview of previous examples.