A139439 Numbers n such that primorial(n)/2 + 4 is prime.

1, 2, 3, 4, 7, 18, 21, 70, 76, 323, 340, 556, 572, 3433, 5457, 5897, 10820

Offset

1,2

Comments

a(17) > 25000. - Robert Price, Nov 11 2016

Links

Table of n, a(n) for n=1..17.

Mathematica

k=1/2; a={}; Do[k=k*Prime[n]; If[PrimeQ[k+4], Print[n]; AppendTo[a, n]], {n, 600}]; a (* Vladimir Joseph Stephan Orlovsky, Aug 20 2008; corrected by Ray Chandler, Jun 16 2013 *)
Position[#/2+4&/@FoldList[Times, Prime[Range[600]]], _?(PrimeQ[#]&)]// Flatten (* The program generates the first 13 terms of the sequence. To generate more, increase the Range constant, but the program may take a long time to run.*) (* Harvey P. Dale, Mar 20 2021 *)

Prog

(PARI) n=0; t=1/2; forprime(p=2, 1e9, n++; t*=p; if(ispseudoprime(t+4), print1(n", "))) \\ Charles R Greathouse IV, Apr 28 2015

Crossrefs

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

Sequence in context: A179985 A338928 A110705 * A352902 A119330 A373392

Adjacent sequences: A139436 A139437 A139438 * A139440 A139441 A139442

Keyword

nonn,more

Author

Artur Jasinski, Apr 21 2008

Extensions

a(1)=1 inserted and a(12)-a(13) from Ray Chandler, Jun 16 2013

a(14)-a(16) from Robert Price, Nov 11 2016

Status

approved