XKCD has a different random number: https://xkcd.com/221/

Stray thought: Why 4 and 9? Because the joke is funniest if the number is completely ordinary.

0 and 1 are special and so are all prime numbers. 6 is out because it's the maximum die throw. And one figure is more ordinary than two figures, or negatives, or decimals. That leaves 4 and 9.

That makes 4 and 9 the only two uninteresting numbers, which is interesting, so they’re out too!

Douglas Adams said the same about 42. It’s the answer because it’s completely banal.

Everyone knows that six is the most boring number. https://youtu.be/G4OTRRmyTAA?feature=shared

How come prime numbers are special but squares aren’t? 4 and 9 both being squares seems to be a more striking commonality than your logic here…

Yeah. Alternative explanation: I'd say 3 and 7 are out because they often come up in fairy takes etc as magical. 5 is out because it's half of ten and the number of fingers. 2 is out because it is too small.

The perfect squares are the most ordinary?

What about 8?

Maximum throw for a battle axe in 5e d&d, of course.

I dunno actually. Maybe because 4*2=8? The two picks have the property of not being related really.

8, 16, 32, 64 pop up a lot in computer circles.

Oh, right! I forgot about it. I guess 8 would do too.