Elementary Papers at ArXiv Inspired by this question, at MO i am asking this question.

Can anyone list some elementary articles at ArXiv which can be understood by High-School/Undergrad Students. I am asking this because, i would like to see some interesting papers and articles to learn something new. If the paper is very much advanced then its of no use to me since i haven't learnt enough Math. I have been searching around for past two hours and i couldn't find a single paper which i could comprehend. Article which i would like to see:-


Interesting proofs of some Elementary number Theory results.
Interesting identity involving Infinite series.
Interesting articles in Basic Abstract Algebra ( concerning Groups and Rings.)
Your favorite article. ( Make sure its elementary enough!)


The best example of what type of articles i am looking for can be found in the answer given by Bill here:


Characterizing continuous functions based on the graph of the function


This is an interesting article. I really enjoyed reading it since i could understand it.
A similar paper to Yuval's answer, which is also quite elementary, is Doyle (and Conway)'s Division by Three. I don't think it requires any advanced knowledge, and is rather interesting.
Sometime in the near future I plan on posting a paper in the General Mathematics section that may be what you're looking for, but for the time being you can find the paper here.