I was not able to find on Wikipedia or on the fandom (Ayame Himuro, Shinya Yukimura). The 1st episode doesn't quite say explicitly, but...
It says Ayame in particular however has a goal of winning the Fields Medal specifically, where according to Wikipedia
With the exception of two PhD holders in Physics (Edward Witten and Martin Hairer),[20] only people with a PhD in mathematics have won the medal.
This must mean that Ayame's major is almost definitely specifically in maths/applied maths/stats (unlikely theoretical maths) instead of something like physics, computer science, information science, etc, but I guess possibly mathematical physics, mathematical computer science (if there's such a thing), etc