Trying to read Simple Wikipedia's Mathematical Induction article:
https://simple.wikipedia.org/wiki/Mathematical_induction
In many of the images, like this one:
https://wikimedia.org/api/rest_v1/media/math/render/svg/8aca5140d2bef31cc6ec27c34ace175533d0685d
There is a 2 to the right sorry, left of the summation symbol. What does it mean?