You say potato, I say aardappel, as far as what the correct word order is. This XF40 fills in the 1783 slot of my prime number set. Only need 1753 to finish the 1723-1951 run, and I think it needs to be gold.
I'm not exactly sure. I was probably just wondering what dates were prime numbers, then saw there were a lot of good coin dates in that run and decided to work on a set and see where it took me. Here's a link to my PCGS showcase set.