History of the Basel problem

Question

Why were the people of the $18$th century interested in the Basel problem?

(The Basel problem asks for the value of $\sum\limits_{n=1}^{\infty}\frac{1}{n^2}$).

Answer 1

$\quad$ Because the divergence of the famous harmonic series has already been known for centuries by then, so, in time, they naturally became curious in the convergence and value of its generalization, especially in light of the infinitesimal calculus introduced independently by Newton and Leibniz in the century before.