OP: Mathematics. My signature says so.
What kind of maths interests you?
When you major in maths you have to pick 1 out of 4. There is applied, pure (my favourite 2), statistics and discrete (both are highly involved with statistics and probability - probably my 2 least favourite forms of maths)
Problem is, it gets more complicated. Once you choose pure maths, you have to decide if you want to major in algebra, analysis, or topology (though of course there's a fair bit of overlap). Then once you choose analysis, you have to decide between linear and nonlinear analysis. And so on and so on...
And discrete maths isn't really that involved with stats and probability at all, to the best of my knowledge.