Question 25
There is a unique function $f: \mathbb{N} \rightarrow \mathbb{R}$ such that $f(1) \gt 0$ and such that
$$
\sum_{d \mid n} f(d) f\left(\frac{n}{d}\right)=1
$$
for all $n \geq 1$. What is $f\left(2018^{2019}\right)$ ?
$$
\sum_{d \mid n} f(d) f\left(\frac{n}{d}\right)=1
$$
for all $n \geq 1$. What is $f\left(2018^{2019}\right)$ ?