Just in case any else is wondering: there are only 83 right-truncatable primes (RTP) and that is it. There's two constraints that let you see this "immediately"

Just in case any else is wondering: there are only 83 right-truncatable primes (RTP) and that is it. There's two constraints that let you see this "immediately": 1. An RTP must start with {2,3,5,7,9}; and, 2. An RTP must end with {1,3,7,9}. So, let's take the largest RTP (73939133) and try to "extend" it: there are only four possible extensions: 73939133[1], 73939133[3], 73939133[7], 73939133[9]. None of these are prime. This holds for the other 8-digit RTPs. Therefore, there is no extension to a 9-or-longer RTP. Thus, the list is exhaustive.