title: How many different ways are there to create a wall with bricks?
body: <p>How many different ways are there to create a wall that length is n and height is 2 with bricks ? 
  Our bricks sizes are 2x1 and 1x1. And bricks are two-dimensional. </p>
  
  <pre><code>For example;
  if n=1, we need one 2x1 or we need two 1x1 bricks    
          so result is 2 different way
  
  if n=2, we need two 2x1 (vertical and horizontal) 
          or we need four 1x1 bricks                    
          so result is 7 different way
  
  if n=3, result is 20 (Unfortunately I'm not sure :/)
  </code></pre>
  
  <p>... etc.</p>
  
  <p>I need an algorithm according to this results, but I didn't associate this results with each other. 
  Can you help me please ?</p>