Double exponential function
A double exponential function is a constant raised to the power of an exponential function. The general formula is f ( x ) = a b x = a ( b x ) {\displaystyle f(x)=a^{b^{x}}=a^{(b^{x})}} (where a>1 and b>1), which grows much more quickly than an exponential function.
Source: Wikipedia — Double exponential function (CC BY-SA 4.0)