title: Hard Big O complexity for 3 loops
body: <p>I try to calculate Big O complexity for this code but I always fail.... </p>
  
  <p>I tried to nest SUM's or to get the number of steps for each case like:</p>
  
  <ul>
  <li>i=1 j=1 k=1 (1 step)</li>
  <li>i=2 j=1,2 k=1,2,3,4 (4 steps)</li>
  <li>. . . . . . . . . . . . . . .</li>
  <li>i=n (i said n = 2^(log n) j = 1,2,4,8,16,.....,n k=1,2,3,4,.....n^2 (n^2 steps)</li>
  </ul>
  
  <p>then sum all the steps together, I need help.</p>
  
  <pre><code>for (int i=1; i&lt;=n; i*=2)
  
     for (int j=1; j&lt;=i; j*=2)
  
        for(int k=1; k&lt;=j*j; k++)
  
             //code line with complexity code O(1)
  </code></pre>