Despite having recently owned one of these, I still can't tell with these things. It's a 1942 d mercury dime.
there were supposed to be varieties of them but that one is strange. There is a shadow of the 4 to the left of the normal 4 just as the 1 is a shadow to the left of the real 1. This may actually be a 42 over 41 but not one of the popular ones as pictured in books such as the Red Book.
I assume you are asking because of the slight bump at the top of the 2. But the 4 should be doubled and there should be a bump at the bottom of the 2 as well. It isn't.
It might be worth a try sending it in to PCGS for grading and verification. If it is a variety of the 42.41 they would know and it would be labled as such making it worth something.
It doesn't look like the 42/1-D dime. The "shadowing" below and to the left of the 4 appears to be machine doubling. As mentioned the 4 on the overdate should show doubling, and it would be similar to the doubling shown on the picture posted by Dockwalliper with distinct notching on the foot and the crossbar of the 4. (The direction of the doubling is a little different but the notching should still be clear.)
