Double exponential function

A double exponential function is a constant raised to the power of an exponential function. Examples include:


 * Double Mersenne numbers
 * Fermat numbers
 * Mills primes
 * The largest known prime as a function of the number of years since the discovery of 180 * (2127 - 1)2 + 1
 * The number of non-self-crossing paths in a game of as a function of the number of discs