Are you sure that's really the hiring process you want?
Junior devs were more recently in school, which is the last time such knowledge is needed. If you have actual technical challenges relevant to your work, why not take that hint and shift the interview to something that might possibly come up on the job and that isn't trivial for a junior dev?
Instead of finding out what that candidate was good at, you just found out which academic trivia he doesn't remember, and that he has a low tolerance for irrelevant bullshit.
There were no trivia involved. I wrote the sequence and explained it - it's not hard to grasp. It's a simple for loop in the easiest solution and a simple recursive method if they want to show off.
I like recreational mathematics too. Is the Fibonacci sequence related to the job in any way? If not, I say it's trivia.
Look, someone looking for their first coding job is surely willing to walk you through CS101 assignments. It's a fine icebreaker if someone has no industry experience.
Someone more senior should be trying to have an entirely different conversation with you. Do you understand and value what they bring to the table that a junior dev doesn't? Will you adapt to take advantage of their strengths, or will you insist on following your process just because it's your process? Is there space for them to make a contribution or are you just looking for someone who will code up what you ask for?
Interviewing is a mutual search for fit. There wasn't one. Maybe that's because you weeded out someone who couldn't complete a freshman homework assignment with help. Maybe not.
Junior devs were more recently in school, which is the last time such knowledge is needed. If you have actual technical challenges relevant to your work, why not take that hint and shift the interview to something that might possibly come up on the job and that isn't trivial for a junior dev?
Instead of finding out what that candidate was good at, you just found out which academic trivia he doesn't remember, and that he has a low tolerance for irrelevant bullshit.