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A139439 Numbers n such that primorial(n)/2 + 4 is prime. 24
1, 2, 3, 4, 7, 18, 21, 70, 76, 323, 340, 556, 572, 3433, 5457, 5897, 10820 (list; graph; refs; listen; history; text; internal format)
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 *)

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: A217289 A179985 A110705 * A119330 A084644 A208729

Adjacent sequences:  A139436 A139437 A139438 * A139440 A139441 A139442

KEYWORD

nonn,more

AUTHOR

Artur Jasinski, Apr 21 2008

EXTENSIONS

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

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

STATUS

approved

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Last modified February 16 15:55 EST 2020. Contains 331961 sequences. (Running on oeis4.)