/page​/4​/?c=1-211609
What is the '/?c=1-211609' and why does it exist in that URL?

Recently, I've been noticing pages getting indexed on my blog that end with random strings such as what I pasted above. Where do they come from? How do I stop them? So far, I've been using the Redirection Tool to simply redirect /page​/4​/?c=1-211609 to /page​/4​/ - because I'm worried about potential duplicate content from these strings.

Any help would be greatly appreciated!