A generalized repunit PRP (base 907).
7331 is the smallest odd prime p such that (907^p-1)/906 is prime.
For the smallest odd prime p such that (n^p-1)/(n-1) is prime (2<=n<=1024, n is not a perfect power), the top 10 currently known (n,p) are (sorted by p): (152,270217), (18,25667), (333,9743), (907,7331), (536,6653), (922,5987), (469,5987), (702,5897), (1012,5749), (683,5483).
Currently, there are no known primes of the form (n^p-1)/(n-1) with odd prime p for n = 184, 185, 200, 210, 269, 281, 306, 311, 326, 331, 371, 380, 384, 385, 391, 394, 396, 452, 465, 485, 487, 511, 522, 541, 570, 574, 598, 601, 629, 631, 632, 636, 640, 649, 670, 684, 691, 693, 711, 713, 731, 752, 759, 771, 795, 820, 861, 866, 872, 881, 932, 938, 948, 951, 956, 963, 996, 1005, 1015. All of these n have been searched to at least p = 7000 with no primes found.

To be completed...