It's a worthy question, and there may well be one.<p>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:<p><a href="https://www.reddit.com/r/math/" rel="nofollow">https://www.reddit.com/r/math/</a><p><a href="http://www.mathoverflow.net/" rel="nofollow">http://www.mathoverflow.net/</a><p><a href="https://math.stackexchange.com/" rel="nofollow">https://math.stackexchange.com/</a>
Not all math, all the time, but: <a href="https://news.ycombinator.com/submitted?id=ColinWright" rel="nofollow">https://news.ycombinator.com/submitted?id=ColinWright</a>