The sum of all counting numbers equals WHAT?

This is the second half of a lesson, watch the first half here: http://youtu.be/yudhkUUzAgY This is a well-known and hugely controversial result. The "proof" I've demonstrated is not the only way to show it - there are far more sophisticated and convincing ways to do it - but suffice to say that I went through it to raise questions and provoke thought rather than to make a statement about its validity or otherwise! Hope it makes you think.