A function, defined on the set of positive integers, is such that f(xy) = f(x) + f(y) for all x and y. It is known that f(10) = 14 and f(40) = 20.
You can get the values of f(2) (which is 3) and f(5) (which is 11) pretty easily meaning you can get the values of any number which has only prime factors of 2 and/or 5, but is it possible to find the value of, for example, f(3)?