Help with Math/Computer related gift

Hello everyone! I want to get a gift that doesn't cost too much for someone who loves computers, engineering, math and science in general and is studying them. They are a person who loves learning things logically instead of learning them by heart. This especially applies to math, which they love a lot to the point where they watch math YouTube videos on the regular. I am a very close friend of theirs, but unfortunately, I am not smart or well versed in those topics, so I would appreciate it if someone could give me just a couple of ideas or even keywords would help. Thanks in advance <3