5

This number is a prime.

(5, 7, 11, 13) is the first tetrad of successive primes p < q < r < s such that (p+q) divides r*s+1, i.e., (5+7) divides 11*13+1. The next such tetrad is (47, 53, 59, 61). Is there other such tetrad? [Loungrides]