 Two-index antisymmetric representation

The two-index antisymmetric representation of $SU(N)$ is the exterior square of its fundamental representation. For $N\ge 3$, it has dimension $N(N-1)/2$, Dynkin index $N-2$, and cubic anomaly coefficient $N-4$ in the same normalization. For $N=2$, the Dynkin index formula still applies in the stated normalization, but every symmetric cubic trace vanishes, so the stated fundamental-normalized cubic anomaly coefficient is not defined.