It has come to my attention that there is a group of users in MSE (myself included) who want to share their own mathematical challenges.
Thus, I have made a proposal in Area 51: Math Challenges.
There have been previous debates on whether challenges/contests should be posted on MSE. Using this question and this one as examples, it can be seen that some people object, some are in favour, and some are in favour given some conditions they've proposed. I believe that this would be completely resolved if there were another site specifically for these types of posts.
A clear distinction between Puzzling SE and this (future) site is that the former site doesn't allow purely mathematical problems. For example, this post of mine was closed there, because "it appears to be a mathematics problem, as opposed to a mathematical puzzle."
Users who are interested in the creation, sharing and answering of mathematical challenges are more than welcome to follow the proposal. In the meantime, a bonus is that you can start thinking of challenge problems to be posted in the "example problems" section :)
If you wish to further discuss this, feel free to use this chatroom
Updates from Area 51 Discussions:
How will this community deal with homework type questions? answered + accepted