It's the mathematical equivalent of dyslexia: http://bodyodd.msnbc.msn.com/_news/2011/05/31/6732939-bad-at-math-or-is-it-dyscalculia?gt1=43001

#@!

Interesting. There is definitely a disconnect between someone's ability to do theoretical mathematics (which is pure logic) and someone's ability to do arithmetic.

Some high functioning autistics for example can do legendary calculations in their heads but absolutely can not grasp mathematical theory or proofs. It makes sense that it could also be the other way around. I think your ability to do the theory says more about "intelligence" because that is just applied logic but arithmetic seems to be a complete hit or miss.

Now, it is worth mentioning that the greatest mathematicians could also do arithmetic very well. If you study mathematics very long (especially number theory) you'll see why that can just make it easier to get a feel for what the theory is doing.

Carl Friedrich Gauss in particular was known to be a living computer. He could even calculate logarithms in his head very quickly. I'm very good at arithmetic (when I don't have an audience) but some of the calculations I've read about Gauss doing sound very humbling.

On a somewhat related topic, there is a popular myth that Einstein is a good example of a great scientists who could not do math very well. That was just Nazi propaganda. After they kicked out the Jewish professors they could not admit they kicked out some great scientists so they made up a lot of stories about how Einstein flunked basic algebra and all his theories were wrong. Well intending algebra teachers embraced the myth about him flunking algebra to encourage students.