Explicit congruences for the class equations $H_{-7p}(X)$ and $H_{-28p}(X)$

A computational proof is given for congruences modulo $p$ for the class equation $H_{-28p}(X)$, when the prime $p$ satisfies $p\equiv 3$ (mod $4$), and for the product $H_{-7p}(X)H_{-28p}(X)$, when $p\equiv 1$ (mod $4$).