Solution (source code)

= Solution

The vacuum is unique, so $N_0=1$. The stress tensor is the spin-$2$ irreducible representation of $SU(2)$ and has $2j+1=5$ states. At the next level, a translation of spin $1$ gives
$$
1\otimes2=3\oplus2\oplus1.
$$
Stress-tensor conservation makes the spin-$1$ divergence a null <conformal descendant>, leaving dimensions $7+5$. Hence
$$
\boxed{N_0=1,
\qquad N_1=5,
\qquad N_2=12.}
$$