When we have two topological spaces, $(X, \tau_X)$ and $(Y, \tau_Y)$ it is easy to check that for $f: X \rightarrow Y$ continuity implies sequential continuity. I'm wondering what do we have to assume for $X$, $Y$ for the converse to hold: here, sequential continuity vs. continuity, are given two sufficient properties ($X$ being sequential, $X$ being first countable). Can it be switched with something else? In particular I'm interested if it holds when $X$ is locally compact and Hausdorff, $Y=\mathbb{K}\in \{ \mathbb{R},\mathbb{C}\}$.
I'd like just a hint, not full proof.