For example:
"2 + 1 = ?": you are expected to answer with a number to complete the equation. The question mark is a good cue -- you know to answer with a number and not, for example, "addition".
"5 x 7 = ?": the same formula as before. You now safely assume that math -- especially math with a "?" after an equals sign -- should be answered with a number.
After that, it degenerates into vague riddles where you're left to guess at the intentions of the author, quite literally. The first place this becomes immediately frustrating is: "2,3,5,7,11,13,17 What are they called?"
Early versions of this game omitted the second line, leading people to guess "19" as a continuation of the prime sequence.
Other popular answers are "prime" or "primes", but the ONLY acceptable answer is "prime numbers." There is no clue leading to the acceptable answer and the only possible way to get it is trial and error or sheer luck.
Primed by that, we face the next problem: "3.14159265..."
Given past history, we can guess that the author either wants us to continue the sequence (unlikely, given the lack of _ or ? cues) or name the sequence. This would be much clearer with the addition of the words "What is" at the beginning -- this is frustrating BY DESIGN, not clever BECAUSE OF design.
A great example of this is the VERY NEXT problem: "1+2+3+...+999+1000"
Given the previous cues (? or _ to show a numerical answer is required, ... to show a sequence to be named), the expectation is that this should be named... however, the author really wants the sum of integers 1-1000. Again, this could have been solved easily with a simple, CONSISTENT cue.
Imagine trying to onboard users and you just say "a date box" without any indication of what they're supposed to use it for or what the consequences of it are.
This game does not build any confidence and should not be likened to good UX design at all.