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A067027
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Numbers n such that (primorial(n) + 4)/2 is a prime.
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25
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1, 2, 3, 4, 6, 10, 11, 12, 15, 17, 29, 48, 63, 77, 88, 187, 190, 338, 1133, 1311, 1832, 2782
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Numbers n such that [A002110(n)/2]+2 is prime.
These primes are products of consecutive odd primes plus 2: 2+[3.5.7.....p(n)] if n is here.
a(19)-a(22) are Fermat and Lucas PRPs. (Primorial(2782)+4)/2 has 10865 digits. PFGW Version 1.2.0 for Windows [FFT v23.8] Primality testing (p(2782)#+4)/2 [N-1/N+1, Brillhart-Lehmer-Selfridge] Running N-1 test using base 5 Running N+1 test using discriminant 13, base 1+sqrt(13) (p(2782)#+4)/2 is Fermat and Lucas PRP! - Jason Earls (zevi_35711(AT)yahoo.com), Dec 12 2006
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MATHEMATICA
| p = 1; Do[p = p*Prime[n]; If[PrimeQ[(p + 4)/2], Print[n]], {n, 1, 400} ]
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PROG
| (PARI) n=0; pr=1/2; forprime(p=2, 1e4, n++; pr*=p; if(ispseudoprime(pr+2), print1(n", "))) \\ Charles R Greathouse IV, Jul 25 2011
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CROSSREFS
| Cf. A002110, A067024, A065026.
Sequence in context: A122397 A047417 A066936 * A005457 A005453 A180242
Adjacent sequences: A067024 A067025 A067026 * A067028 A067029 A067030
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Dec 29 2001
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Dec 30 2001
a(19)-a(22) from Jason Earls (zevi_35711(AT)yahoo.com), Dec 12 2006
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