>>14304652u substitution, 3d volumes from 2d functions, riemann sums, area between two curves, etc and a bunch of little problems in course math
riemann hypothesis on my own time
and since you said "anything you learned in the past 3 months," i'm learning 3d modelling, reading GEB/learning about music history, getting caught up on new research for a project of mine (biology related), and tried to learn python/ML but was too stew peed to figure out how to use anaconda