I was wondering if it's possible to express the following sum as a function of $n$: $$ \sum_{d|n} [\phi(d)]^2 $$
similarly to the known relation: $$ \sum_{d|n} \phi(d) = n $$ where $\phi$ is the totient function.
2026-04-02 13:02:40.1775134960
Divisor sum of totient function squared
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