K3 elliptic genus and Mathieu-M₂₄ moonshine (string-theory)

String-theory application of L0 elliptic-curve and Dirichlet-L-function. The elliptic genus of the K3 complex surface, φ_{K3}(τ, z), is a weak Jacobi form of weight 0 and index 1 whose value at z = 0 equals the Euler characteristic χ(K3)…