title: Generate a repeating sequence
body: <p>I need to generate a vector of the following format using R:</p>
  
  <pre><code>1:10, 1:10, 11:20, 11:20, ... 121:130, 121:130
  </code></pre>
  
  <p>Is there an easier way than creating 12 vectors and then repeating each one twice?</p>