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A139602
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The smallest prime p that makes the pair p+/-6n both primes while no other pair of p+/-6k+6*n, 0<k<n both primes.
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2
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11, 19, 61, 43, 97, 163, 191, 229, 283, 223, 743, 991, 541, 457, 877, 1327, 1049, 1321, 1733, 1307, 1987, 6011, 2971, 5153, 2029, 8693, 2551, 4789, 5407, 2129, 6473, 4481, 4889, 4217, 7951, 11743, 13789, 9851, 7253, 11491, 20393, 17231, 9749, 20747, 6599, 13873, 16369, 15461, 17123, 13451, 9967, 26959, 21089, 41863, 27437, 26003, 40189, 18661, 16673, 64693
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Dickson's conjecture implies that this sequence is infinite. [Charles R Greathouse IV, Mar 22, 2011]
2a(n)=(p-6n)+(p+6n)
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LINKS
| Charles R Greathouse IV, Table of n, a(n) for n = 1..1000
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EXAMPLE
| For n = 1, 11-6n=5, 11+6n=17, are both primes, and for any prime number p smaller than 11, it is impossible that p-6 is prime;
For n = 2, 19-6n=7, 19+6n=31, are both primes,while 19+6*1=25 is not prime. For primes p<19, either p+/-6 are prime pairs, or p+/-12 are not a prime pair;
...
for n = 6, 163-6n=127, 163+6n=199, are both primes,while 163+6*k, k=1,2,4 and 163-6*k, k=3,5 are not primes. For primes p<163, either exists prime pair p+/-6k, 0<k<6, or p+/-36 are not a prime pair.
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MATHEMATICA
| BothPrime[p_, k_] := PrimeQ[p + 6*k] && PrimeQ[p - 6*k]; f[n_] := Module[{p, k}, p = Prime[PrimePi[6*n] + 1]; While[k = 1; While[k < n && ! BothPrime[p, k], k++]; k < n || ! BothPrime[p, n], p = NextPrime[p]]; p]; Table[f[n], {n, 60}]
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PROG
| (PARI) a(n)=forprime(p=2, default(primelimit), if(!isprime(p-6*n)|!isprime(p+6*n), next); for(k=1, n-1, if(isprime(p-6*k)&isprime(p+6*k), next(2))); return(p)) \\ Charles R Greathouse IV, Mar 22, 2011
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CROSSREFS
| Sequence in context: A139829 A138355 A178385 * A080789 A057770 A080788
Adjacent sequences: A139599 A139600 A139601 * A139603 A139604 A139605
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KEYWORD
| nonn
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AUTHOR
| Lei Zhou (lzhou5(AT)emory.edu), Mar 22 2011
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