Problem Statement

The sequence of primorial primes is given as the increasing values of n where primorial(n) ± 1 is prime. Noting that the n'th primorial is defined as the multiplication of the smallest n primes, the sequence is of the number of primes, in order that when multiplied together is one-off being a prime number itself.

Generate and show here the first ten values of the sequence.

Show the first twenty members of the series.

Let's start with the solution:

primoprim=: [: I. [: +./ 1 p: (1,_1) +/ */\@:p:@i.


   primoprim 600x
0 1 2 3 4 5 10 12 23 65 67 74 166 170 171 286 309 351 383 456 563 589