Divergent series Quote by Matt Parker

““If you recall, in Ramanujan's letters to English mathematicians, he claimed that 1 + 2 + 3 +...= -1/12. He was so surprised when Hardy took him seriously that he replied on 27 February 1913 in the following words: 'I was expecting a reply from you similar to the one which a Mathematics Professor at London wrote asking me to study Infinite Series and not fall into the pitfalls of divergent series. If I had given you my methods of proof I am sure you will follow the London Professor. I told him that the sum of an infinite number of terms of the series: 1 + 2 + 3 + 4 +...= -1/12 under mu theory. If I tell you this, you will at once point out to me the lunatic asylum as my goal.' It turns out that not only had Ramanujan independently rediscovered the Bernoulli numbers, but he may have found more than one way to prove that 1 +2 +3 + 4 ...= -1/12. This is now called Ramanujan summation and gives us an insight into the ways in which the sum of a sequence can be divergent. Of course, the sum of all the positive whole numbers is infinite, but if you can somehow peel that infinity back out of the way and look at what else is going on, there's a -1/12 in there.””

— Matt Parker