Mathieu moonshine conjecture for Fourier coefficients of a mock modular form

Let $H(\tau)$ be a mock modular form with Fourier coefficients $A_n$, and let $M_{24}$ be the simple sporadic Mathieu group. Mathieu moonshine conjecture. The Fourier coefficients $A_n$ of $H(\tau)$ are given as special sums of dimensions of irreducible representations of $M_{24}$. The conjecture is presented as an analogue of Monstrous Moonshine; a precise description of the special sums is required for its full formulation.