Motivation: It's an elementary exercise to show that the number of solutions to the equation $\phi(x)=n$ is finite for any $n$, where $\phi$ is the Euler-phi function. Of course, counting the number of solutions is another matter.

Question: For a given $n$, can we describe the number of solutions to $|\phi^{-1}(n)|=m$? In other words, I want to know about how often the number of solutions to the equation $\phi(x)=n$ is $m$, for a given $m$, as $n$ varies. Since it wouldn't surprise me if this is way too hard, can we at least say something similar about finiteness?

Some Remarks on Euler's $\phi$-Function,Acta Math. (1958), Vol. 4, pp. 10-19. – Salvo Tringali Oct 2 '12 at 10:23Carmichael's totient function conjecture, with a story behind it: Carmichael had published an alleged proof (Carmichael,On Euler's $\phi$-Function,Bull. AMS, Vol. 13 (1907), pp. 241-243), and even developed a method of finding a solution for each m (R.D. Carmichael,Notes on the Simplex Theory of Numbers,Bull. AMS, Vol. 15 (1909), pp. 217-223), to the extent of proposing the question as an exercise in his 1914 monograph on the theory of numbers. It took more than... (TBC) – Salvo Tringali Oct 2 '12 at 10:56Note on Euler's $\phi$-Function,Bull. AMS, Vol. 28 (1922), pp. 109-110), with the result that the question is still today broadly open. In spite of the fact that Dickson, in the 2005 edition of hisHistory of the Theory of Numbers(Vol. 1, p. 137), states that the conjecture was proved in Carmichael's original 1907 paper. – Salvo Tringali Oct 2 '12 at 10:57