title: how to code : sum_{n=1}^{100}\frac{2^{n}}{(n-1), in R
body: <pre><code>sum_{n=1}^{100}\frac{2^{n}}{(n-1)
  </code></pre>
  <p>I tried substituting parenthesis over curly brackets, which shows an error message. I am a beginner in R. With the problem above, I do not understand the requirements to produce code.</p>