In this paper we study conjugacy classes for pivotal fusion categories. In particular we prove a Burnside type formula for the structure constants concerning the product of two conjugacy class sums of a such fusion category. For a braided weakly integral fusion category $\mathcal C$ we show that these structure constants multiplied by $\mathrm{ dim}(\mathcal C)$ are non-negative integers, extending some results obtained by Zhou and Zhu (see \cite{ zz}) in the settings of semisimple quasitriangular Hopf algebras.
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