I saw a really odd thing today. A friend of mine on tribe.net posted the following puzzle. "What is so special about the number 8549176320?"

I'll ruin the suspense for you. It's the digits 0-9 sorted by their English names.

I've also found it asked in several places on the web while searching on google.com. What surprised me was that people often also answer "it's divisible by all the single digit numbers except 0!" The problem is that it's not divisible by 7.

8549176320 / 7 = 1221310902.85714... (the digits "285714" appear to repeat but I haven't verified)
I only noticed it myself because I was having fun with the number and printed out its factors:

    % factor 8549176320
    8549176320: 2 2 2 2 2 2 2 2 2 2 3 3 3 5 61843
(This is a standard program on most UNIX and Linux systems.)

The number 7 is not a factor! (But it's cool that a huge prime number, 61843, is a factor.)

Anyone with a calculator would see this. So why do so many people state that it's divisible by 7? I think it must be that people have heard it somewhere and are just repeating it, or maybe they googled it and are repeating the wrong answer that someone else had posted.

It's an interesting illustration of how people can see something stated authoritatively and repeat it as if it was correct, when a simple check would show that it's not.

Update: It was suggested to me that it might not be apparent that 8549176320 / 7 has a remainder on a calculator that shows only 10 digits. So there's an explanation of the thing.

Last modified:
Wed Aug 9 23:47:41 PST 2006