You can google "reducing to common denominator".

and define D and N_x for x from 1 to n

I have a vague idea from my math classes but the way the problem is exposed makes almost no sense to me, si D supposed to be the common denominator of what ?

In test1 of "Run" (Your test cases) there is only one "subtest". In "Submit" there are 8 tests. You can succeed in subtest1 of test1 but fail in one of the 7 other tests. Print the input to see what is going on in your code which caould have a bug. Be sure that there are no errors in the tests.

Then how do you explain that the solution compiles fine and the test passes, see this screen shot: https://gyazo.com/b1758e407d465130c11b85c8b50da267? But it then fails to compile when the tests in the Test1 class that I cannot see are added (when I submit). I also get the error message which says there is a problem in the Test1 class: https://gyazo.com/8b63f384fb8c06fe889110f23318edb3. I fail to see how this is not pointing to an error in the Test1 class. I am happy to send you my solution for testing.

It would help if you showed the steps in the middle. Just showing [N_1, D] and then [N_n, D] doesn't make any sense to me. Show me what happens in between.

nice, learned a lot from this fizzbuzz implementation