Ask HN: HN like website for Mathematics?

It's a worthy question, and there may well be one.

But I've noticed over the years that, often, when we ask "What is the HN for XYZ," the answer often turns out to be ... HN.

I don't know of anything that's an exact correspondence, but some things that are kinda-sorta that, if you squint real hard:

https://www.reddit.com/r/math/

http://www.mathoverflow.net/

https://math.stackexchange.com/

Not all math, all the time, but: https://news.ycombinator.com/submitted?id=ColinWright

You can take a look at https://math.stackexchange.com/

Stack overflow with more fluid discussions could the answer. With a wiki it would be even more accessible and lively