That's a truly diabolical streak. Congrats! I remember seeing somewhere that they stopped giving lingots to the app users, but still give them to the web users. As they're now bringing the web version close to the app, I guess we'll soon lose all the privileges, including the free test-outs. I already have an idea for the workaround. But it sucks how they constantly change the rules of the game.

I don't know about maths, but there's a lot of gamified sites for learning/practicing programming languages - Codecademy (basic), Codewars, Hackerrank etc. Somehow I can never stick with these, maybe because learning a programming language is much easier, but unlike the natural languages, programming knowledge feels so much more useless when you're actually not using it for any practical purposes.