Diagram of the summation notation.
<ul><li><a href="//commons.wikimedia.org/wiki/File:Greek_uc_sigma.svg" title="File:Greek uc sigma.svg">Greek_uc_sigma.svg</a>: <a href="//commons.wikimedia.org/wiki/User:Andux" title="User:Andux">Andux</a></li>
<li>derivative work: <a rel="nofollow" class="external text" href="http://kulla.me/">Stephan Kulla</a> (<a href="//commons.wikimedia.org/wiki/User:Stephan_Kulla" title="User:Stephan Kulla">User:Stephan Kulla</a>)</li></ul>
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>