The numbers 13, 127, and 241 are an interesting “prime pair permutation” trio. Each number is prime, and concatenating any permutation of a pair of these numbers also makes a prime. For example,  = 13,127 and  = 24,113 are both prime.
This week’s GeekDad Puzzle of the Week is straightforward, but may take a little brain power. How many sets of numbers under 1,000 are there that are “prime pair permutation” quartets? That is, how many sets of four primes are there with 3 or fewer digits that can be selected pairwise in any combination to be stuck together in either order that always make a new prime?
For your chance at a $50 ThinkGeek Gift Certificate, send your responses into GeekDad Central by end of day Saturday. All correct answers (and reasonably well reasoned incomplete or incorrect answers) will be entered into a random drawing the the ThinkGeek prize — just in time for Halloween shopping!
Good luck, and happy puzzling!