I believe there is a [email protected].
If you hit Communities and filter by All, then search Formula, you'll find it!
Though, you may notice there is an issue with hitting subscribe, it might just say that you're subscription is pending due to heavy traffic and I read somewhere that it is a visual bug. However, even while pending it will show up in your subscribed list and content!
One of the upcoming Lemmy updates (I guess 0.19 or so) will allow linking communities on two or more instances. I'm not really interested in a pending status most other communities don't have.