It threads off in a counterclockwise direction.
Get the longest chisel or heavy standard screwdriver you can find and while the belt is still on, set up the chisel on the left edge of the nut and use a heavy hammer to give it a sharp smack. It sould break loose pretty easy and spin right of by hand the rest of the way.
Having the right tool is nice but as Stumpy said this works as I did it a few times myself. I had an old big screwdriver blade that was about 2 to 3 ft long and the handle broke off years earlier so I used it like a chisel and it worked great for this. Like was said make sure you get it near the edge so it hits its force in the right direction and usually one good hit with a nice size hammer did it for me. Ron