I've edited in a link to a wikipedia article which refuses to show up. Can't see anything wrong with this entry?
Your original URL (http://en.wikipedia.org/wiki/Fisher–Yates_shuffle) contained an en dash character (Unicode 8211, –, etc...), and SO's Markdown engine tends to get confused by such characters in URLs.
Fortunately, the link works just as well with a hyphen (-), so I just replaced it.
You might find it helpful that Firefox will automatically escape such characters when you copy the URL out of the address bar, because so many sites have problems with them. The escaped form looks like this: