Ramanujan wrote:

Dear Sir, I am very much gratified on perusing your letter of the 8th February 1913. I was expecting a reply from you

similar to the one which a Mathematics Professor at London wrote asking me to study carefully Bromwich's Infinite Series

and not fall into the pitfalls of divergent series. … I told him that the sum of an infinite number of terms of the series: 1 +

2 + 3 + 4 + · · · = −1/12 under my theory. If I tell you this you will at once point out to me the lunatic asylum as my goal. I

dilate on this simply to convince you that you will not be able to follow my methods of proof if I indicate the lines on which

I proceed in a single letter

So this equation is over a hundred years old and was solved by a mathematician with no formal training who was arguably

the greatest ever. Had that been mentioned in the video then I would have accepted it without question. Argument from authority is of course not infallible but Ramanujan was a complete one off. He even managed to surpass Hardy who was regarded as one of the greatest mathematicians of his generation. He is to mathematics what Einstein is to physics. So he

ought to be a household name but famous mathematicians tend to be completely unknown outside of mathematics which

is rather unfortunate because famous scientists by comparison are not