What mathematics are complex enough to be interesting but easy enough for a brainlet to understand ?

Ancient Greek geometry.

Planar geometry was mentioned above. Essentially very similar.

much of number theory, actually

post-anabelian froeboid geometrics

basic cryptography

Really this. Only the most retarded of brainlets can't do simple calculus like derivatives or sigma notation.

Analytic/Non-Eucidean Geometry

Yeah this too. Planer Geometry is good.

I personally like just standard Vector Calculus, if you want to speak about something complex but meaningful, due to its applications in science.

Basic Group Theory

algebraic topology

All of it. What's interesting is usually what is challenging, so it changes as you advance.

the mathematics of fucking killing yourself you pitiful brainlet

you won't be able to understand shit if you dont have what it takes

Hodge conjecture

f(x)=a-x^2

Basic set theory

If it's interesting its easy to understand by definition, you just need to know where to start.

>(2)

category theory