Official solution
\[{2^{{1 \over 4}}}{.4^{{1 \over {16}}}}{.8^{{1 \over {48}}}}{.16^{{1 \over {128}}}}\] ...
= \[{2^{{1 \over 4} + {2 \over {16}} + {3 \over {48}} + ...\infty }}\]
= \[{2^{{1 \over 4} + {1 \over 8} + {1 \over {16}} + ...\infty }}\]
= \[{2^{\left( {{{{1 \over 4}} \over {1 - {1 \over 2}}}} \right)}}\]
= \[{2^{{1 \over 2}}}\]