I've heard verse 20 heaps of times: "For where two or three gather together as my followers,s I am there among them."

But do yourself a favour and read the verses that come before. Puts a bit of a different spin on it. I don't exactly know what it means (more research needed) but I'm pretty sure that most of the times I've heard this verse quoted, it's been used completely out of context.

Matthew 18:18-20