Thank you for the clarification. I found websites with .co before the county's 2 letter code. As I am not from the US, most of the domain names in the country where I reside has an ending of .co. Anyway, I think its the same as .com but maybe its used for local websites.
I am considering the extension .co.in but I would like to have more answers from different countries. My real target is the international window but I'm thinking it would be hard to get traffic because of many websites that are the same as mine.
My goal is to let my students learn on how to solve the same math problem with different solutions from other countries.