NEED HELP WITH SUMMATION NOTATIONS

TOP NUMBERIS 6 OVER A SIDEWAYS Z BOTTOM NUMBER IS A N=2 THAN THERE IS (2N-1) NEED TO KNOW HOW TO WORK THIS PROBLEM. i AM TRYING TO HELP MY SON WITH HIS HOMEWORK

looks like you are describing Sigma notation.

here is a webpage that explains it in the first 2 pages.
http://www.mathcentre.ac.uk/resources/leaflets/firstaidkits/2_22.pdf

for yours it can be expanded to

3 + 5 + 7 + 9 + 11

at this point just add them up