ORIGINAL: SharpProp
When I turn the nut, the crank turns with it. The prop can spin a little without turning the crank but the nut seems to be jammed up.
I believe there is metal debris preventing the nut to reach the end of the shaft (or the prop would have go flying after getting loose); hence, forcing the nut out will cause further damage to the shaft up to the end.
As recommended above, cut and remove the prop; then, try to screw-in the nut, cleaning the threads with wire brush and some light lubricant.
If still tight, I would cut the nut down to the shaft.
Sometimes, that, and the generated heat, are sufficient to loose the nut enough to liberate the interference.