I have been gone for long and also haven’t been having much time on my hands for writing new posts but starting today, I will try to change that and be more frequent in my blogging and present new articles form whatever I am reading and various other articles that interest me.

Recently I came across a particularly fascinating divisibility test for 7 in the blog of Tanya Khovanova who’s quite famous among the math blogging community.

Here is the post :http://blog.tanyakhovanova.com/?p=159

It basically gives you a graph that;s constructed by a certain David Wilson, a fan of sequences who happened to be a guest blogger on the blog i mentioned above.

The main point of the test is as follows :

By David Wilson :

I have attached a picture of a graph.

Write down a number

n. Start at the small white node at the bottom of the graph. For each digitdinn, followdblack arrows in a succession, and as you move from one digit to the next, follow 1 white arrow.For example, if

n = 325, 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,

nis divisible by 7.

Now this made me look out for any other possible interesting ways to test the divisibility by 7 and that is ofcourse keeping in mind that the method i come across should be simpler then direct division process ;).

Another process that has been described in this paper is pretty simple nd staright forward but just a starting point in the author’s idea of divisibility by primes. Do give it a look if you are interested.