The kata description Exceptions part confused me more than helped. Maybe just change the wording a bit to make it clearer (I´m not a native English speaker so it migth have been a factor as well)

thanks for this kata g964, your katas are always simple but somehow challenging. Whenever I see your name I know that the kata is worth a try

Changing the structure of the tests in C# would make much easier to figure out where you´re failing.
It is not a issue, but would help a lot.

g964, this was a really good kata but I believe there is some room for improvement in the Kata wording. It was hard to me, a non native English speaker, to get the acronym for greatest common divisor (GCD), and I also had some dificulty to understand some of the functions to implement, so maybe an numerical reference to the functions dependencies would help (Ex:
4: p(n) with parameter n: returns an array of n unique prime numbers(unique results of 3) (not tested)
5: 5: maxp(n) with parameter n: returns the biggest prime number of the sequence p(n) (max of function 4) # (tested)
6: anOver(n) with parameter n: returns an array (n terms) of the a(i)/i for every i such g(i) != 1 (using functions 1 and 2)(not tested but interesting result)
).

Anyway it is a really good kata =)

It was hard to understand what to do given that there is no local test cases. Adding a local test and maybe adding a return values would make it easier to understand.