Math is a bit too broad. From personal experience, the most relevant topics for programmers are Linear Algebra and Discrete and Combinatorial Algebra.

Eh I mean, I think there's a certain discipline that comes with studying any branch of math to a certain degree of rigor. But yes, linear algebra and discrete math are probably the most useful. I think control theory and optimization are under appreciated amongst programmers though.

I'd recommend statistics specifically. Comes up everywhere and it's easy to be wrong about if you don't dig into it.

Second this, if you only work through the Khan Academy stuff on the various things like scatter plots, standard deviation, the normal distribution, etc. you'll be much better off for it.