The 1817/3 Half Dollar is an enigmatic overdate that defies explanation. If it were a leftover die from 1813, one would expect the 13th obverse star to show the notched point that is believed to be the "signature" of engraver John Reich. Reich resigned his position in March 1817, after which the notching of the stars ended. This suggests that the new engraver simply made an error by punching a 3 into the die, then corrected it with the proper 7 punch. But, why would the engraver have picked up a punch for a 3? That would have been an egregious oversight on the engraver's part, especially since he was four year's away from a need for a 3, plus there is no U.S. coin from 1817 where a 3 might be used in either a legend, motto, or denomination.
Regardless of the reason for this variety, it is extremely popular with collectors. Only one die combination (Overton 101, and it's later die state Overton 101a) utilize this obverse. In most grades, the 1817/3 Half Dollar is fairly common, but in Mint State, it becomes very rare.
Possibly acquired by Cornelius Vermeule or Cornelius Vermeule Jr., before 1950 - Cornelius C. Vermeule III Collection - Stack's 9/2001:236 (this sale was originally planned for 9/2011 in New York, but was canceled because of the attack on the World Trade Center) - D. Brent Pogue Collection