\[
\sum_{m_{3}} e^{-\beta u s n}=e^{0}+e^{-\beta u s}+e^{-\beta 2 u s}+\cdots
\]
Converge para
\[
A=\frac{1}{1-e^{-\beta u s}}
\]
\(\boxed{A = \frac{1}{1 - e^{-\beta u s}}}\)
Step 1 :Given summation: \(\sum_{m_{3}} e^{-\beta u s n}=e^{0}+e^{-\beta u s}+e^{-\beta 2 u s}+\cdots\)
Step 2 :Recognize this as a geometric series with a common ratio of \(e^{-\beta u s}\)
Step 3 :Calculate the sum of the geometric series: \(A = \frac{1}{1 - e^{-\beta u s}}\)
Step 4 :\(\boxed{A = \frac{1}{1 - e^{-\beta u s}}}\)