Several times I have come across about this problem. Solve $\phi(n)=m$ where $m$ is a given natural number. I did some investigation on the solution process, but till now I have not found any general procedure. May be I am wrong or may be my search is still require to go further, but I would like to get the suggestion from the experts around here. Can you please tell me or at least provide me any link where I can find the general process of solving this types of number theoretical equation? Suppose that $m=12, 13, 15$ are given. How shall I proceed?
Thanks in advance
