Rationals are countable. It's actually pretty neat if hard to express as a function, but that's not required. http://www.cwladis.com/math100/Lecture5Sets.htm#:

Rationals are countable. It's actually pretty neat if hard to express as a function, but that's not required. http://www.cwladis.com/math100/Lecture5Sets.htm#:~:text=the%20natural%20numbers%3F-,The%20Cardinality%20of%20the%20Set%20of%20Rational%20Numbers,-We%20recall%20that http://www.cwladis.com/math100/Lecture5Sets.htm#:~:text=the%...