  We study the s-numbers of elementary operators acting on C*-algebras. The
main results are the following: If $\tau$ is any tensor norm and $a,b\in B(H)$
are such that the sequences $s(a),s(b)$ of their singular numbers belong to a
stable Calkin space $J$ then the sequence of approximation numbers of
$a\otimes_{\tau} b$ belongs to $J$. If $A$ is a C*-algebra, $J$ is a stable
Calkin space, $s$ is an s-number function, and $a_i, b_i \in A,$ $i=1,...,m$
are such that $s(\pi(a_i)), s(\pi(b_i)) \in J$, $i=1,...,m$ for some faithful
representation $\pi$ of $A$ then $s(\sum_{i=1}^{m} M_{a_i,b_i})\in J$. The
converse implication holds if and only if the ideal of compact elements of $A$
has finite spectrum. We also prove a quantitative version of a result of
Ylinen.
