Wilkinson's polynomail is a terrible joke played on numerical
analysis. By tradition, the function is f(x) = (x - 1)(x - 2)...(x -
20), giving a function with real roots at each integer from 1 to 20.
This function is generalized and allows for n and the function
value is f(x) = (x - 1)(x - 2)...(x - n). The default of n is
20.