Divisibility by 7

divisibility by 7
 
If the number is 325, then follow 3 black arrows, then 1 white arrow, then 2 black arrows, then 1 white arrow, and finally 5 black arrows.
If you end up back at the white node, n is divisible by 7.
 
Source:   http://blog.tanyakhovanova.com//?p=159
 
Why does it work?
 
 
 

About benvitalis

math grad - Interest: Number theory
This entry was posted in Math Beauty and tagged . Bookmark the permalink.

3 Responses to Divisibility by 7

  1. Husain Alshehhi says:

    I believe that you mean that I have to start from 0. And if I ended at 0, then the number is divisible by 7.

  2. Is it some sort of finite state automata? I seem to remember making diagrams like these for numbers in my theoretical computer science class.

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