For each sequence, find a formula for the general term, \( a_{n} \).
\[
\begin{array}{l}
\frac{1}{2}, \frac{1}{4}, \frac{1}{8}, \frac{1}{16}, \ldots a_{n}=\square \\
\frac{1}{2}, \frac{2}{3}, \frac{3}{4}, \frac{4}{5}, \ldots \quad a_{n}=\square
\end{array}
\]
\[
4,6,8,10, \ldots \quad a_{n}=
\]
\( \square \)