We investigate sc 7 (n), the number of self-conjugate 7-core partitions of size n. It turns out that sc 7 (n) = 0 for n ≡ 7 (mod 8). For n ≡ 1, 3, 5 (mod 8), with n ≡ 5 (mod 7), we find that sc 7 (n) is essentially a Hurwitz class number. Using recent work of Gao and Qin, we show that2 ). This fact implies several corollaries which are of interest. For example, if −D n is a fundamental discriminant and p ∈ {2, 7} is a prime with ord p (−D n ) ≤ 1, then for every positive integer k we have