Plus there’s no good way within the context of the puzzles to find out what mathematical trick you need if you don’t already know; you need to go find a virtual water cooler.
I may simply be biased because each year it reveals how little I know, but I much prefer interesting programming problems that don’t require me to go to Reddit, read other people’s description of what math is required, go learn the math involved, and then finally implement a solution.
Most of the problems are around searching a space for some solution or just simulating some state changes. Recent problems involved implementing a higher dimensional version of Conway's game of life[0], a simple arithmetic expression evaluator [1], or a simulator for a simple number game[2] e.g.
The most recent one[3] involves solving a jigsaw puzzle by using a simple backtracking search (or any number of other methods). It's a bit complex, but not reliant on a particular math trick.
The vast majority of the problems in advent of code shouldn't require any math tricks, though they're often complex and involved, particularly as the month goes on.
[0] https://adventofcode.com/2020/day/17
[1] https://adventofcode.com/2020/day/18
For 2015, and 2020 so far - its mostly text parsing, data structure building and basic iteration/permutations.
I stopped doing advent this year when I realized I was spending more time debugging my parsing than I was actually solving the problems. It's just not that fun for me to sometimes spend 2+ hours finding parse bugs before moving on to the actual puzzle.
Perl Advent Calendar is my jam.
They are almost all algorithm based rather than math based.
By the way, adventofcode.com is currently ongoing. Though the challenges are easy compared to the projects in this list, I highly recommend it. It covers problems you might face in big projects. With these small puzzles it's easy to experiment. It prepares you for bigger things.