= Symmetric square of the sl3 representation of highest weight (2,1)
{title2=$S^2\Gamma_{2,1}$}
For the <special linear Lie algebra> $\mathfrak{sl}(3)$, with <Dynkin labels> indexing irreducible <highest-weight representations>,
$$
S^2\Gamma_{2,1}\cong\Gamma_{4,2}\oplus\Gamma_{3,1}\oplus\Gamma_{0,4}\oplus\Gamma_{1,2}\oplus\Gamma_{2,0}.
$$
The summands have dimensions $60,24,15,15,6$, summing to $120=15\cdot16/2$. The identity follows from the <formal character of a weight module> formula $\chi_{S^2W}(z)=(\chi_W(z)^2+\chi_W(z^2))/2$ and the <Weyl character formula>.
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