Game Of Powers

Tumpaa recently learned the concept of powers and she loves experimenting with it. Tumpaa randomly selects two numbers $a$ and $N$.Now she tries to find the value of $a^N$,lets say that is $k$.But Tumpaa is curious still so she decides to find the sum of digits of $k$.Eg if $a$ was 2 and $N$ was $4$,$k$ will be 16.Sum of digits $k$ will be 7.Tumpaa is still curious,she wants to know if sum of dig