Not a formally trained mathematician, but I think this story is a stunning example of just how much innate mathematical ability the human brain contains. Also,

Not a formally trained mathematician, but I think this story is a stunning example of just how much innate mathematical ability the human brain contains. Also, it's noteworthy that the ability to describe complex mathematical concepts without being able to write them down formally seems to be a common thread in a certain kind of genius (e.g. Einstein).