Task: Text Categorization
Input (English): This function is approximated for large numbers by Stirling's approximation. The traveling salesman problem can be solved in Big O of this function. The pi function and gamma function extend this function to complex numbers. This function appears in the denominator of the Taylor series of polynomials, and this function is said to grow faster than all polynomial and exponential functions. Often used with combinations and permutations, for 10  points, name this mathematical function, defined as the product of all positive integers less than or equal to n, denoted by an exclamation point.
Output (English): Science