I had a college professor like that. He was nearly unable to perform arithmetic, and would ask for the answer from the class. I wouldn't say he was dyslexic (I

I had a college professor like that. He was nearly unable to perform arithmetic, and would ask for the answer from the class. I wouldn't say he was dyslexic (I have no idea), but he certainly couldn't perform mental arithmetic. But he was fabulous at math. We'd often ask him questions far outside the realm of the textbook and class just for the privilege of seeing an extremely good mind tackle a problem. So I disagree with the OP. The fact that some mathematicians brains work that way is not evidence that they all do, nor is it evidence that it is helpful or preferable.