title: PHP Riddle. The function of the pyramid
body: <p>I have a riddle for you.</p>
  
  <p>I need a function that displays the number of pyramid structures.</p>
  
  <p>Example: echo getNumber(7)</p>
  
  <p>Output: 12345677654321</p>
  
  <p>In this case, do not use  outside functions and operators.</p>
  
  <p>From the mathematical symbols use only addition. <strong>Dont use for/while/implode/range/count.</strong></p>
  
  <p>Maximum use of one condition.</p>
  
  <p>Good luck!</p>