Factorable function

This has a recursive definition, relative to a collection of elementary operations (e.g., sum, product) on other factorable functions, starting with some set of primitive functions. For example, starting with the power functions, $LaTeX: ax^n$, for any $LaTeX: a$ and $LaTeX: n$, and allowing only the sum operation, we can obtain all polynomials. The polynomial $LaTeX: x + 2x^2 + 9x^3$ factors into 3 parts.