31 is a prime number

Michele ordered "6" plastic clips and a slender rail for a sliding door in our laundry cupboard.  So, when I went to the local hardware store on my bicycle today to pick it up, I was rather surprised at how large the package was.  Fortunately, my single bungee cord was sufficient to secure it safely to the back on my bike.  When I got home, and opened the package, I found "31" plastic clips with "6" mounting screws.  No matter how you cut it, 31 is a prime number and is, therefore, not divisible by "6".  So, the only conclusion which I can draw is that someone in the packageing department at Reno-Depot made an inadvertant arithmetical error.  Considering that I only needed 2 clips to fix the door, I'll bring the extra 25clips back to the store so that someone doesn't get into trouble.