Let N=((64)64)64 N=(64)642 N=(1+63)642, let 642=n Expanding by binomial $\begin{aligned}
& \mathrm{N}=(1+63)^{\mathrm{n}}=1+{ }^{\mathrm{n}} \mathrm{C}_1 63+{ }^{\mathrm{n}} \mathrm{C}_2(63)^2+\ldots . \
& =1+63 \lambda=1+7(9 \lambda)
\end{aligned}$ Remainder when divided by 7 is 1