Answer by Jeff Atwood for Bug in feed URL with # in the tag name [Chrome only]

What is c%2523 ?

Checking my ASCII chart, let's see:

25 = %  
23 = #  

So after doing a little conversion, these URLs are in the form of

/feeds/tag/c%2523 ---> /feeds/tag/c%23

So these are just.. invalid. How did you get them?