2020/21 AHSMC Part 1 Problem 9

For a positive integer $N$, let $S(N)$ denote the sum of the digits of $N$. Consider the sequence $a_1 = 2$, $a_n = \bigl(S(a_{n-1})\bigr)^2 - 1$ for $n \ge 2$. The term $a_{2020}$ is equal to