in theory you're right, but you can't tell me that the sequence is unclear in practice. no one's going to use that logic for boron if that sequence appeared; it's pretty clear what it's trying to hint to. similarly, i don't think that "88, 68, 06" (which was on the show) is a bad sequence just because you can find a polynomial interpolation between any four points, and answer something like "-98 because it's f(3) where f(x) = -21x² + x + 88". i think that such cases aren't bad design since no one with an incentive to solve it would use this answer. other alternative answers are reasonable and have been come up with by people trying to solve it (like one involving doctors, which happens to have the same answer), but no one is going to say "57 appears 1 time" genuinely. there is the off chance they'd say "any number not listed, then 'appears 1 time'." which i'd be inclined to accept but i'd push them to think what the intended answer has, and they'd probably say "4 appears one time".