The code given below shows these visible points is a hack. In fact it actually displays more points that are off the screen now. As a challenge, see if you can understand the code and find another point that is actually plotted off the screen.

Here is a picture of the graph,

Here is the code being used. The code lists elements a=[1,...,15]. Here is a picture of the code from a=1 to a=4. The code is the same pasted all the way down to a=15. Please explain how the code works and provide a code for a point that is not pictured in the graph but is still visible.

The (a*gcd(a,4)^20,4*gcd(a,4)^20) is the code provided on each term of a.