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 A073703 Smallest prime p such that also p+prime(n)*2 is a prime. 16
 3, 5, 3, 3, 7, 3, 3, 3, 7, 3, 5, 5, 7, 3, 3, 3, 13, 5, 3, 7, 3, 5, 7, 3, 3, 31, 5, 13, 5, 3, 3, 7, 3, 3, 13, 5, 3, 5, 3, 3, 31, 5, 7, 3, 3, 3, 11, 3, 3, 3, 13, 13, 5, 7, 7, 31, 3, 5, 3, 7, 3, 7, 3, 19, 5, 7, 11, 3, 7, 3, 3, 43, 5, 5, 3, 3, 19, 3, 7, 3, 19, 11, 19, 11, 3, 43, 13, 5, 7, 3, 3, 13, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If Polignac's conjecture (1849) is correct, the sequence is defined for all n (as is A020483). Also: least k-prime(n) such that k-prime(n) and k+prime(n) are both primes. - Pierre CAMI, Aug 27 2004 LINKS Charles R Greathouse IV, Table of n, a(n) for n = 1..10000 EXAMPLE n=5: prime(5)=11; 2+11*2=24, 3+11*2=25 and 5+11*2=27 are not prime, but 7+11*2=29 is prime, therefore a(5)=7. MATHEMATICA f[n_] := Block[{k = Prime[n], p = Prime[n]}, While[ !PrimeQ[k - p] || !PrimeQ[k + p], k++ ]; k - p]; Table[ f[n], {n, 95}] (* Robert G. Wilson v, Aug 28 2004 *) PROG (PARI) forprime(q=2, 500, forprime(p=2, default(primelimit), if(isprime(2*q+p), print1(p", "); next(2))); error("Not enough precomputed primes")) \\ Charles R Greathouse IV, Aug 21 2011 (Haskell) a073703 n = head [p | p <- a000040_list, a010051 (p + 2 * a000040 n) == 1] -- Reinhard Zumkeller, Oct 29 2013 CROSSREFS Cf. A073704, A001747, A000040, A020483. Cf. A010051. Sequence in context: A124887 A304903 A097524 * A175019 A097519 A133773 Adjacent sequences:  A073700 A073701 A073702 * A073704 A073705 A073706 KEYWORD nonn AUTHOR Reinhard Zumkeller, Aug 04 2002 EXTENSIONS Merged with Pierre CAMI's submission of Aug 2004 - R. J. Mathar, Jul 29 2008 STATUS approved

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Last modified October 23 23:51 EDT 2019. Contains 328379 sequences. (Running on oeis4.)