A triple of vertices in a graph is a frustrated triangle if it induces an odd number of edges. We study the set Fn ⊂ [0, n 3 ] of possible number of frustrated triangles f (G) in a graph G on n vertices. We prove that about two thirds of the numbers in [0, n3/2] cannot appear in Fn, and we characterise the graphs G with f (G) ∈ [0, n3/2]. More precisely, our main result is that, for each n ≥...