This problem is probably a rather trivial one, since I have the impression, that it is a textbook-style one, but nonetheless somehow it won't give in. Here it is:
I have to show that there exists a (unary) recursive function, that has code $c$ and also takes the constant value $c$ (i.e., it outputs its own code).
I am pretty sure, I have to use Kleene's (second) recursion theorem, that says that for a given (total) recursive function $f:\mathbb{N} \rightarrow \mathbb{N}$ there is a number/code $c$ such that $\phi_c=\phi_{f(c)}$ (where $\phi_a$ is the partial recursive function that has code $a$), but I can't figure out how...