SEAMO 2027 - Paper E - SET 07 - Self-study Question 25

For every positive integer $n$, let $a_n$ be the last two digits of $6^n$, treated as a number. For example, $a_1=06,a_2=36,a_3=16$. Find the last two digits of $a_1+a_2+\cdots+a_{2021}$.