SF Amateur Mathematicians
SF Amateur Mathematicians is an extremely cool math club. It's centrally coordinated from a Meetup page.
After a couple years of anxiously roaming the streets in search of a conference room it can call home for more than a couple sessions, the club is now giving Noisebridge a shot. The first meeting here will be Thursday, February 25, 2016.
All the meetings we've had thus far have either been a talk or a discussion of a reading. Other ideas for formats are welcome, but that's what it's been like so far.
Topics generally assume some collegiate mathematical background, though regular attendees range from enthusiasts who never took an upper division math course to folks who have a PhD in the subject. Everyone is welcome.
For more information please see the Meetup page.