X4 having the same problem. My formula works for smaller values but the final test case gives the following error:

170970902404966449586247098818855152577703936966215095276168985530690669141903684898 should equal
170970902404966462328920047488181969596690166234976092377640121561715772973645152611

does something happen when the numbers become really large? I can't see why it should be inaccurate for this value yet correct for the others

Update: not sure if it will help others but making sure that only type'int' was in the equation solved my large number inaccuracy. Best of luck everyone