Primorial prime

A primorial prime is a number that is one less or one more than a primorial and also a prime number. The first eight primorials are

5, 7, 29, 31, 211, 2309, 2311, 30029

The largest known primorial primes are p₅₉₀# - 1 and p₁₃₉₁# + 1.

Reference

The article on primorials at http://mathworld.wolfram.com/Primorial.html, from Wolfram Research, the makers of Mathematica 4.