Off topic (because the topic is about very big and very small numbers, and I think it's mind boggling):
1 + 2 + 3 + 4 + 5 + ... = -1/121
Only if you use a very specific treatment of infinity that also happens to be useful in physics (edit: or was it quantum mechanics.. hmmm, already forgot) because it actually ends up matching what they're seeing 1 + 2 + 3 + 4 + 5 + ... = -1/121
( saw that vid a while back - there's all sorts of mathematical oddities in those channels, well worth subscribing. )