Good Riddles

 
Riddle #16 (medium)

Question: I can run but never walk. Wherever I go, thought are close behind me.

What am I?

Question: 8,549,176,320 What makes this number unique?

Riddle #525 (medium)

Question: In Michigan you cannot take a picture of a man in a green hat.

Why?

Question: What goes up but never comes down?

Riddle #456 (medium)

Question: I am a big threat to humanity,
but you wouldn't get rid of me even if you could.

What am I?