Official solution
\[\begin{aligned}
&\begin{aligned}
& 64^{64} \Rightarrow(63+1)^{64}=63 \lambda+1 \\
& 64^{664^{64}} \Rightarrow(63+1)^{64^{64}} \\
& 63 \lambda_1+1
\end{aligned}\\
\&\text { Required remainder when divided } 7 \text { is } 1 \text {. }
\end{aligned}\]