Solution
= Solution
Wilson gives $18!\equiv-1\pmod {19}$. Since $18\cdot17\equiv2$, $2\cdot16!\equiv-1$, hence $16!\equiv9\pmod {19}$.
= Solution
Wilson gives $18!\equiv-1\pmod {19}$. Since $18\cdot17\equiv2$, $2\cdot16!\equiv-1$, hence $16!\equiv9\pmod {19}$.