A139440 Numbers n such that primorial(n)/2 - 4 is prime.

3, 4, 5, 7, 12, 15, 26, 31, 50, 71, 186, 273, 366, 1542, 1929, 3687, 4407, 15395, 15433

Offset: 1

Author

Artur Jasinski, Apr 21 2008

Keywords

• nonn

Comments

a(20) > 25000. - Robert Price, Dec 03 2016

Crossrefs

Cf. A067026, A067027, A139439-A139457, A103514.

Programs

Mathematica

k = 1; a = {}; Do[k = k*Prime[n]; If[PrimeQ[k - 4], Print[n]; AppendTo[a, n]], {n, 2, 366}]; a

Extensions

a(14)-a(15) from Ray Chandler, Jun 16 2013

a(16)-a(17) from Robert Price, Aug 16 2016

a(18) from Robert Price, Dec 03 2016

Added missing term, 15395 by Robert Price, Dec 28 2016