Can you onside kick after a safety or does the receiving team have to touch the ball first?

Yes. It's happened several times but I believe this was the last.

"Still, Cleveland was in it to the end, even after giving up a safety with :08 left. The Browns recovered an onside kick and threw deep on the final play. It fell incomplete"

http://www.cbssports.com/nfl/gametracker/recap/NFL...

Edit: So actually occurring in a game isn't enough proof for the two idiots who gave me a thumbs down? How about showing some proof to the contrary? Like a rule or something. I can't prove the rule's not in there (that would be proving a negative). It's happened several times in the nfl. That should be enough proof.

Edit (II); Here's the rulebook. Show me where I'm wrong.

http://static.nfl.com/static/content/public/image/...

No because the team was tackled or ran out of their endzone has to kick to the other team

it is a free kick from the 20 .. like a punt

The team that scores the points also gets the ball

Nope. The team that gave up the safety has to free kick or punt from their 20.