• What’s so special about 10,213,223?

    I posed this question on Friday: what’s so special about 10,213,223?

    Answer: It’s a self-describing number. Read it in English as, “One zero, two ones, three twos, two threes.” That’s a description of what’s in the number. Not with me yet? Read that English bit in quotes again and write down each number as it appears (ignoring the pluralization “s”s).¬†Go on, write it down as you read the bit in quotes: 1…0…2…1…3…2…2…3 or 10,213,223. Isn’t it true that the number so described contains one zero, two ones, three twos, and two threes? Indeed it does! The number describes itself.

    Practical applications: Seriously? You want to know how this is of any use? Well, it isn’t really. But it is related to run-length coding data compression. More in my prior post on the “look and say” sequence.

    • Abraham Verghese uses this number in his 2009 novel CUTTING FOR STONE. It’s used to establish one of the characters (who is in grade school) as a math genius.