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December 07, 2009


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I used to be a lightning calculator as a kid. No real trick, but you have to make the numbers below one hundred your friends: adding, subtracting, multiplying; factors, logs and roots if you want to get fancy. It was a great way to kill time during road trips -- reading made me carsick, and my brother didn't play happily.

Most people can keep seven digits in their head (e.g. a new phone number) without much difficulty, so I don't think this is some mutant ability. Just a lot of rote work that is not necessarily interesting in itself, like exercise.

There's the famous anecdote about Ramanujan and Hardy and a taxi number 1729. Ramanujan commented that it was the smallest number that could be composed of two positive cubes in two different ways. Hardy was amazed.

But really, it wasn't that crazy of Ramanujan. He had to have known 12^3 = 1728 by heart -- how many cubic inches are there in a cubic foot, because of the Imperial system of measurement. But the 729 = 9^3 in "1729" would have been a dead giveaway, because Ramanujan probably had the cubes of the first few integers memorized anyway. So 1729 = 1000 + 729 = 10^3 + 9^3 or 1729 = 1728 + 1 = 12^3 + 1^3. And there just aren't that many possible cases.


You really should come live with us.


We did that sort of thing with our boys for years. Including showing them stuff that they hadn't learned in school yet - simple algebra, etc. They loved it.

I'm reasonably good at mental arithmetic, but have always loved math and numbers.

Loved Carlos's comments.


How the hell did I get through med school? I hate math. It just doesn't make sense to me...

Doug M.


I was just thinking about it this morning -- how I wanted to start David on the times tables.

Doug M.

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