Guest Safety or Encryption Gone Wrong??

While on a recent vacation we stayed with a hotel chain that still used old fashioned keys at their properties. When I checked in I was assigned room F 123 in a particular building and was told that for my protection the room number was not on the key rather there was a coded so they would know what key went to what room. So far so good wright, well not so fast at looking at the key I saw the coded number was 36261. Wow it took all of 5 seconds to break this uber secret encryption algorithm. I would be impressed but my wife figured it out just as fast without saying a word. Better look next time.

So for our second night we stayed at a different property run by the same company same deal classic keys and top secret encoding system. Our room was was cottage 523 sure enough they encoded the key 29395. Does any one else see the pattern?