Please clarify your question. It is not at all clear to me what you are asking. There are (infinitely) many expressions (functions) that bound the expression (function) `n!n^3`. That is a trivial statement. But none of them is constant in `n`.
– walnutFeb 19 '20 at 16:25
Are you perhaps asking for an upper bound not involving factorial (!)? Perhaps involving just polynomial and exponential and logarithmic functions?
– Patrick87Feb 19 '20 at 18:28