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.