This website posts a logic riddle/math problem every day. There's an AI-powered hint and verification system but the problems are allegedly picked by a Human. Regardless, I've looked at a couple of problems already and enjoyed solving them. Here's an example of “today's” problem:
In a city there are 100 people and several clubs. Each club has an odd number of members. In addition, any two distinct clubs always share an even number of members. What is the maximum possible number of clubs?