Functions whose Big O is exponential, O(2n), grow so quickly that they can hardly be plotted on a log-log graph.
If you find that your function cannot be plotted on a log-log graph, try plotting it on a semi-log graph, where the x axis is linear and the y axis is logarithmic.
An exponential function will produce a linear plot on a semi-log graph. Such functions are considered to be intractable, i.e. thay can only be computed when n is relatively small.