title: Getting a sequence like [(list[n-1], list[n+1]), (list[n-2], list[n+2]), ...]
body: <p>I have tried below code</p>
  <pre class="lang-py prettyprint-override"><code>list1 = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
  def fun(num):
      if num in list1:
          print(list1[num-2::-1],list1[num+1::1])
  
  fun(9)
  </code></pre>
  <p>The output is <code>[8, 7, 6, 5, 4, 3, 2, 1] [11, 12, 13, 14, 15, 16, 17, 18, 19, 20</code>]</p>
  <p>But the required sequence is like <code>[8, 10] [7, 11] [6, 12] [5, 13] [4, 14] [3, 15] [2, 16] [1, 17]</code></p>