I was one asked the answer to that with N=6. I noticed the pattern for N ⇐ 5, but I suspected they were trying to trick me so I actually tried to determine it from scratch. (As for the “Obvious for low N, harder to prove for higher N” part, I used the heuristic that if no three of the lines met at one same point inside the circle, I had probably achieved the maximum. It worked.)
OTOH I was once asked “2, 3, 5, 7, what comes next?” and I immediately answered “that’s the prime numbers, so it’s 11”, but there was some other sequence they were thinking about (I can’t remember which).
I was one asked the answer to that with N=6. I noticed the pattern for N ⇐ 5, but I suspected they were trying to trick me so I actually tried to determine it from scratch. (As for the “Obvious for low N, harder to prove for higher N” part, I used the heuristic that if no three of the lines met at one same point inside the circle, I had probably achieved the maximum. It worked.)
OTOH I was once asked “2, 3, 5, 7, what comes next?” and I immediately answered “that’s the prime numbers, so it’s 11”, but there was some other sequence they were thinking about (I can’t remember which).
At least those
Yes, the OEIS is a great way to learn first-hand the Strong Law of Small Numbers. This sequence being a particularly nice example of “2,3,5,7,11,?”.