Not to get meta on you, but you're assuming that I'm assuming. I assure you I'm not assuming anything. I tried it myself, successfully, having never done it before, and it's not that hard to solve. Someone else posted their solution here. Good programmers can come up with that kind of code routinely, mediocre programmers can't. And this is a test to distinguish the classes.

Talking about software design methodology cannot tell me whether someone can write new algorithms correctly. If I have a job that requires people to correctly design algorithms, I think asking questions about algorithm design is entirely appropriate.

I'm not talking about methodology, I'm talking about the interviewer coming up with a problem that would require an algorithm to be designed, whose task it is the interviewees to solve. However, if the interviewer themselves doesn't know algorithms enough to come up with a decent problem....

"rote"?

Are you seriously suggesting that anyone has code for a line of pascal's triangle memorized? Why would they? Just in case they got asked for it in an interview?

This is one of the advantages of this over something like quicksort: it's obscure enough that the candidate won't be able to recite it.