Project Euler Level 9 Badge
I managed to reach Level 9 (225-249 problems solved out of over 615 at the moment). To put this in perspective, there are 21 levels. However even Level 9 has less then 400 members at the moment (2017).
The problems are very challenging, and I admire how clever some people’s solutions are (you can browse what others post as solutions after you submit a correct answer yourself).
It’s a great learning experience if you want to learn how to push coding to the limit and tackle problems involving huge numbers. Brute force approaches seldom work, so you need to think about the mathematics involved as well.
The link to the website is here Project Euler.