You surely know the syntax for multiplication, addition, and exponentiation. So you understand the polynomial in the opening paragraph. I'm sure you know function notation and division, so you understand that P(n)/k is always an integer.
You probably have seen the sigma notation before because that's usually taught in high schools around the world, so you know that the lemma which is not Burnside's is about adding and dividing. You probably have seen the notation |X| to mean absolute value, so perhaps we finally are reaching the limits of your knowledge if it has been a while since you've seen the notation |X| can also mean the size of a set (which is, in a way, a sort of absolute value, mathematicians love type-punning).
I'm sure you've seen function notation f: X -> Y to indicate that f is a function from the set X to the set Y, but I'll believe if you didn't know that [n] is the set {1, 2, 3, 4, ..., n}.
I haven't done a careful calculation here, but I believe as a moderate estimate that this already covers at least 30% of the mathematical symbols in this page.
My point is: the notation isn't probably the problem. You surely have seen these symbols before or can figure out what the individual symbols mean. I daresay the most esoteric symbol here is the Fraktur S for the symmetric group (here for the symmetric group of 6 symbols),
https://en.wikipedia.org/wiki/Fraktur#Unicode
but I assume that if you didn't know what the symmetric group is, the more common notation of S_6 would probably not have helped you much.
So if the notation isn't the problem, I wager that the concepts and the difficulty of absorbing these ideas is the problem. It requires you to compile stuff yourself in your own head.
With programming we are used to a machine doing this for us. We write the code, give it to a machine, the machine basically tells us if we're right or not. With mathematics we don't generally have that machine for all cases. You have to do the work in your own head. The problem isn't the symbols. The problem is that you have to think about them harder, work out what is being multiplied, what are the sets in question, what are the operations, and put them together yourself. You have to read something like not Burnside's lemma and understand what it's saying about permutations and sets and grouping and counting.
Reading mathematics is a special skill. It's slow. It requires you to take out pen and paper and work it out yourself. Yes, like that. You have to do input and output on your own as you do mathematics. It's a unique skill that sadly isn't usually independently taught except at the university level.
The concepts and the work required to understand them are the problem. Not the symbols. The symbols are superficial and easily dispensed with.