No number. Slut is more in attitude and character than a numbers thing.

I know a few girls who have put it about plenty and I wouldn't consider them sluts but have met a few girls who on paper would appear nuns in comparison but come across as slutty.

I guess if I am perfectly honest I would prefer the girl I ended up with to have slept with less people than me but that would probably be a competitive thing than anything else.

In fact both my last two girlfriends had more "notches" than me