The result of multiplying all prime numbers up to and including a given prime number.
For example the primorial of 5 is P(5) = 2 x 3 x 5 = 30
Here are the first few primorials:
P(2) = 2
P(3) = 2 x 3 = 6
P(5) = 2 x 3 x 5 = 30
P(7) = 2 x 3 x 5 x 7 = 210
P(11) = 2 x 3 x 5 x 7 x 11 = 2310
P(13) = 2 x 3 x 5 x 7 x 11 x 13 = 30030
P(17) = 2 x 3 x 5 x 7 x 11 x 13 x 17 = 510510
etc
See: Prime Number