title: What is the sum of a sum?
body: <p>Σ from i=1 to n of(n)(n+1)/2 </p>
  
  <p>What is the upper limit of computation for a give n? is it O(n^3) O(n^2)?</p>
  
  <p>Example:</p>
  
  <pre><code>n=1 , sum =1
  n=2 , sum= 1+ 1+2 ,   sum = 4
  n=3, sum= 1+1+2+1+2+3, sum = 10
  n=4, sum = 1 + 1+2 + 1+2+3 + 1+2+3+4 = 20
  n= 5, sum = 1+ 1+2 +1+2+3 +1+2+3+4 + 1+2+3+4+5 , sum = 35 
  ...
  n=10,  sum = ..... , sum = 220 
  </code></pre>
  
  <p>etc, so what is the upper bound of this computation as a function of N? is it : </p>
  
  <p>O(n^3)?</p>