When I learned about how the sum of a series could be divergent and convergent, I decided to try to find the sum of the square reciprocals to no avail. The proof, obviously at not my level as you can tell, was too difficult to understand (what math branch is required because they mentioned something a Riemann Zeta function).
Is there an alternative proof that would yield the result ${\pi^2}/6$ as well without higher math?