# Only a third are coprime?

Let $$x_1, x_2, x_3, \ldots$$ be all the distinct positive integers satisfying $$\phi(x) = \dfrac x3$$.

Compute $$\dfrac1{x_1} + \dfrac1{x_2} + \dfrac1{x_3} + \cdots$$.


Notation: $$\phi(\cdot)$$ denotes the Euler's totient function.

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