Sum the first n even numbers in a series
Example
{% scaleimage l19_example.png %}
Step 1
Divide the highest number in the series by 2.
{% scaleimage l19_step1.png %}
If you only know n then
the highest number is 2 x n
Step 2
Multiply the result of step 1 by itself plus one.
{% scaleimage l19_step2.png %}